Optimising the application frequency of VectoMax® FG for the control of Ae. albopictus and Culex spp. in the urban environment: findings from a randomised controlled trial

Optimising the application frequency of VectoMax® FG for the control of Ae. albopictus and Culex spp. in the urban environment: findings from a randomised controlled trial | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Optimising the application frequency of VectoMax® FG for the control of Ae. albopictus and Culex spp. in the urban environment: findings from a randomised controlled trial Tim Kirrmann, Thomas A. Smith, Bianca Modespacher, Pie Müller This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7241349/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 27 Nov, 2025 Read the published version in Parasites & Vectors → Version 1 posted 9 You are reading this latest preprint version Abstract Background VectoMax® FG (Valent BioSciences, Libertyville, IL, USA) is a biological mosquito larvicide, combining Bacillus thuringiensis var. israelensis and Lysinibacillus sphaericus . Bacillus thuringiensis var. israelensis demonstrates a low propensity for resistance development, whereas B. sphaericus exhibits prolonged residual efficacy in organically polluted aquatic environments. The manufacturer recommends treatments at least every 4 weeks; however, recent evidence suggests that less frequent applications may achieve comparable efficacy, which is important for reducing operational costs related to larvicide volume and labour as well as reduced environmental exposure. Methods To provide data-driven guidance for vector control programmes, we conducted a randomised controlled trial in Basel, Switzerland, from May to October 2024. A total of 180 catch basins, randomly selected from 768 basins in an urban area infested with Aedes albopictus , were assigned to treatment intervals of 2, 4, 6, 8 or 10 weeks, alongside untreated controls. Emergence traps were used to capture adult mosquitoes developing from larvae within the basins, allowing comparison of mosquito abundance reductions across treatment frequencies. Generalised additive and linear mixed effects models were applied to quantify the effects of larvicide application frequency, temperature, precipitation and time since treatment on mosquito and non-target dipteran populations. Results Suppression of all taxa peaked within 20–30 days post-treatment. Moderate (> 50%) reductions in mosquito abundance were sustained for up to 10 weeks following treatment, with Culex spp. exhibiting persistent suppression exceeding 80% for up to 8 weeks, and Ae. albopictus maintaining comparably high levels of suppression for up to 5 weeks. Conclusion Our findings show that reapplication of VectoMax® FG at 5-week intervals is necessary for sustained suppression of Ae. albopictus and Culex spp. While Culex responded well even at longer intervals, Ae. albopictus required more frequent treatment to avoid rebound. Optimised application frequency not only enhanced control but also reduced variability in mosquito abundance, highlighting the importance of locally tailored treatment schedules in integrated vector management. Mosquito control Bacillus thuringiensis var. israelensis Lysinibacillus sphaericus Aedes albopictus Culex Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Background Climate projections indicate a continued expansion of the range suitable for Ae. albopictus in Europe, raising significant public health concerns due to its competence as a vector for more than 20 arboviruses, including dengue, chikungunya and Zika [ 1 ]. Aedes albopictus has already been associated with multiple chikungunya outbreaks in Italy and France [ 2 , 3 ] and increasing autochthonous dengue outbreaks in Europe. These findings underscore the urgent need for effective mosquito control measures in areas infested with Ae. albopictus [ 4 ]. Like Ae. albopictus, Culex spp. have the potential to transmit viruses, including Japanese encephalitis virus (JEV) [ 5 ], West Nile virus (WNV) [ 6 ] and several other arboviruses [ 7 – 10 ], as well as filarial parasites [ 11 ]. The ecological success of Culex spp. in urban settings is largely driven by the availability of organic-rich water bodies [ 12 ]. Consequently, JEV, WNV, Usutu virus (USUV) and Sindbis virus (SINV) have been found in the European Culex population in urban environments, indicating the importance of Culex spp. control measures [ 13 , 14 ]. Since its first detection in 2003 [ 15 ], Ae. albopictus has also become well established in Switzerland, spreading particularly along major transportation corridors [ 16 ]. In urban settings, mosquito control strategies typically involve a combination of public awareness campaigns to avoid potential breeding sites and larviciding of permanent water bodies such as catch basins [ 17 – 19 ]. In Switzerland, VectoMax® FG – a larvicide that combines Bacillus thuringiensis var. israelensis ( Bti ) and Lysinibacillus sphaericus – is routinely used in public mosquito control programs [ 18 ]. While the manufacturer recommends reapplication every 4 weeks, emerging evidence suggests that longer intervals may still provide effective control and enhance cost-efficiency [ 20 ]. Laboratory studies have shown that formulations combining Bti and L. sphaericus , such as VectoMax® FG, can achieve greater than 80% reduction in both Culex quinquefasciatus and Aedes aegypti populations for up to 8 weeks. This extended efficacy is largely attributed to the synergistic action of the Cyt1Aa toxin in Bti , which facilitates the entry of Bin toxins into the epithelial cells of larvae that are resistant or lack Bin receptors [ 21 ]. To evaluate the effect of VectoMax® FG application frequency on reducing the number of adult mosquitoes, we conducted a randomised controlled trial (RCT) in the St. Johann district in Basel, Switzerland, during the 2024 mosquito season. Catch basins were treated at different frequencies, ranging from 2- to 10-week intervals, and their effects on mosquito abundance were measured via adult emergence traps placed in the catch basins. Methods Study area The St. Johann district, located in the north-west of the city of Basel, Switzerland, was selected for the trial because of its well-documented high prevalence of Ae. albopictus and its strategic importance as the initial point of entry of the species into Basel [ 22 ]. Basel is highly urbanised with dense residential infrastructure and many underground catch basins that provide ideal conditions for container-breeding mosquitoes. Weather data The daily mean air temperature and total precipitation were obtained from the nearest MeteoSwiss stations – Basel-St. Johann (temperature at 2 m above ground) and Basel-Binningen (precipitation). Treatment procedure From a list of 768 catch basins in St. Johann, provided by the local administration, 30 were randomly assigned to each of five larvicide application frequencies – 2, 4, 6, 8 or 10 weeks – or to a negative control group that received no treatment (Fig. 1 ). Each treatment consisted of VectoMax® FG (Valent BioSciences, Libertyville, IL, USA) combining Bti (strain AM65-52) and Lysinobacillus sphaericus (strain ABTS 1743) at a dose of 10 g per catch basin, following the city of Basel’s standard procedure. A pre-measured 10 g cup was used to dispense the granules into each catch basin through a funnel to minimise spillage. Treatments commenced on 29 April and continued until 24 October 2024. During that period, catch basins treated at frequencies of 2, 4, 6, 8 and 10 weeks received 13, six, four, three and two treatments, respectively. Mosquito collection procedure The emergence of adult mosquitoes, and other dipterans, from the selected catch basins was monitored weekly via custom-built adult emergence traps on the basis of the design of Ravasi et al. [ 20 ]. Each trap consisted of a white plastic funnel with a diameter of 16.1 cm. Low-density polyethylene foam (LDPE) was attached around the base to allow the traps to float on the water, resulting in a total diameter of 20.5 cm. The openings of the funnels were 1.7 cm wide and led directly into collection cups, measuring 9.1 cm in diameter and 10.1 cm in height. Each cup had a 5.1 cm opening at the base covered with a fine mesh net. Fine mesh nets with small openings were also attached to the tops of the cups, allowing mosquitoes to enter through the funnel while preventing their escape during cup removal and replacement. Traps were placed inside the catch basins, floating on the water surface to capture emerging adult dipterans. To ensure stability, three 10 cm LDPE foam pieces were attached to the base of each trap (Fig. 2 ). Traps were removed and replaced on a weekly basis, during which their functionality – including net integrity and placement – was checked, alongside catch basin conditions such as water level and the presence of leaves or other debris. Each cup was labelled with the corresponding catch basin ID and the week of collection to ensure traceability of the samples. Mosquitoes were brought to the laboratory and frozen at -18°C for at least 2 hours. The samples were then transferred into 1.5 ml Eppendorf tubes in pools of up to 10 individuals and stored at -18°C until later identification. Mosquito identification At the conclusion of the field season, all frozen insects were identified morphologically to major taxonomic groups under a stereo microscope, using the ‘Reverse identification key for mosquito species’ by the ECDC and the ‘Key to Diptera families – adults’ [ 23 – 25 ]. The taxonomic groups included Culex spp., Chironomidae , Psychodidae and Aedes spp. Specimens belonging to the genus Aedes were further identified to the species level. Data analysis The data were first recorded on paper forms and then transferred to an Open Data Kit database [ 26 ]. Subsequent data analysis was performed in R version 4.51 [ 27 ], including data on the four taxonomic groups Ae. albopictus , Culex spp., Chironomidae and Psychodidae. Abundance was summarised as the arithmetic mean number of specimens per taxonomic group and per adult emergence trap per week, with 95% confidence intervals (CIs) estimated using the R package ‘boot’ [ 28 ], on the basis of 1,000 bootstrap samples. This approach allowed for the estimation of 95% CIs without requiring preliminary assumptions regarding the distribution, thereby providing CIs that more reliably reflect the observed data. To evaluate the effects of larvicide application frequency, temperature and precipitation on mosquito abundance, generalised linear mixed models (GLMMs) and generalised additive mixed models (GAMMs) were developed, using the R packages ‘glmmTMB’ [ 29 ] and ’mgcv’ [ 30 ] respectively. For the models, the temperature was centered around the mean of 19.7°C. To account for potential delays between weather conditions and changes in mosquito abundance several lag periods (0 to 21 days) for both temperature and precipitation were assessed. Based on biological plausibility and preliminary model performance, only a 1-week lag for precipitation was selected for the final models. Owing to overdispersion in the mosquito count data, models were fitted via a negative binomial error distribution, and separate models were constructed for each taxonomic group to account for taxon-specific responses. First, a GLMM with categorical application frequency was used to quantify the associations between application frequency, temperature and lagged precipitation while accounting for temporal and spatial correlation through random intercepts (Eq. 1). Table 1 explains the different variables and model terms used in the statistical models described above. $$\:\begin{array}{c}{\nu\:}_{i}\in\:0.1,\:0.125,\:0.167,\:0.2,\:0.5\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\\\:{log}\left(E\left[{Y}_{i}\right]\right)=\:{\beta\:}_{0}\:+\:\sum\:_{j=1}^{5}{\beta\:}_{j}1\left({\nu\:}_{i}=j\right)+\:{\beta\:}_{7}\tau\:ᵢ\:+\:{\beta\:}_{8}\rho\:\:+\:{\mu\:}_{1}\left[i\right]+\:{\mu\:}_{2}\left[i\right]\#\left(1\right)\end{array}$$ Next, the observed mean trap counts with 95% confidence intervals were plotted to illustrate the relationship between mosquito abundance and time since the most recent treatment. To better understand these trends, model-based estimates of mean trap counts generated from GAMMs were overlaid. To establish a baseline for comparison, initial mosquito abundance was estimated by setting the ‘time since treatment’ to zero in untreated control catch basins. Although equivalent GLMMs using the same predictors yielded lower Akaike information criterion (AIC) values, diagnostic checks revealed consistent nonlinear patterns in abundance over time across all taxa. Therefore, GAMMs were selected for their greater flexibility in capturing these dynamics (Eq. 2). $$\:\begin{array}{c}{log}\left({\eta\:}_{i}\right)=\:f\left({t}_{i}\right)+\:{\beta\:}_{2}\tau\:ᵢ+\:{\beta\:}_{3}{\rho\:}_{i}\:+\:{b}_{1}\left[i\right]\:+\:{b}_{2}\left[i\right]\:\#\left(2\right)\end{array}$$ Finally, a GLMM including application frequency as a continuous variable was used to estimate the dose-response relationship between application frequency and the number of emerging adult insects. The predicted insect reduction rates were derived across application frequencies and taxonomic groups (Eq. 3). $$\:\begin{array}{c}{log}\left(E\left[{Y}_{i}\right]\right)=\:{\beta\:}^{0}+\:{\beta\:}^{1}\upsilon\:ᵢ\:+\:{\beta\:}_{2}\tau\:ᵢ\:+\:{\beta\:}_{3}\rho\:\:+\:\mu\:1\left[i\right]+\:\mu\:2\left[i\right]\#\left(3\right)\end{array}$$ Although the inclusion of precipitation and temperature did not consistently improve model fit, as indicated by the AIC, across all taxonomic groups, these variables were retained to ensure comparability between groups. Table 1 Variables and model terms used in the linear models Variable Description Units Y₁ Observed mean mosquito count at trap i \(\:\stackrel{-}{x}\) E[Y i ], \(\:{\eta\:}_{i}\) Expected mosquito Mean count (per trap) υ i Frequency of larvicide application at trap i - 𝟙(υy i = j) Indicator function for application frequency level j \(\:\in\:0.1,\:0.125,\:0.167,\:0.2,\:0.5\) τ i Mean temperature at trap i during sampling period °C ρ i Precipitation one week after sampling at trap i mm t i Time since larvicide was last applied at trap i Days µ 1 [i] Random intercept for trap location 1-180 µ 2 [i] Random intercept for sampling day Calendar days b 1 [i] Random effect for trap (in GAMM context) 1-180 b 2 [i] Random effect for day (in GAMM context) Calendar days f() Smooth function (thin plate spline) - β₀ Intercept (fixed effect) Mean count (per trap) βⱼ Coefficients for model predictors Mean count (per trap) SE_β₁ Standard error of frequency coefficient - x Input frequency sequence used for predictions seq(0, 0.5, by = 0.001) R Predicted mosquito reduction = 100(1 − exp(β 1 x)) % Results During the sampling period, seven catch basins were excluded due to the absence of water accumulation (4), construction work obstructing access (1), flooding of a residential area due to blockage after heavy rain (1) and incidental larvicidal treatment by a third party (1) (Fig. 1 ). A total of two, two, one, one, one and zero catch basins were excluded for the control and the 2-, 4-, 6-, 8- and 10-week intervals, respectively. The remaining 173 catch basins were monitored weekly. Owing to illness no sampling was executed from 23 September to 30 September 2024. A total of 2,076 trap observations were recorded with 12.6% of the data containing missing values, primarily due to trap displacement caused by heavy rainfall. More than half of the collection cups (58.8%) were empty, whereas the remaining ones contained one or more individuals, resulting in a total of 4,936 collected dipterans. Owing to desiccation or physical damage, 3.4% of specimens could not be reliably identified, leaving 4,768 individuals for taxonomic classification. Most of the specimens caught in the traps were Culex spp. (53.2%), followed by Chironomidae spp. (31.1%), Psychodidae (6.4%) and Ae. albopictus . (5.8%). A randomly selected subsample of 81 Culex spp. was identified as entirely Culex pipiens , except for one specimen that could only be identified to the Culex genus level, supporting the assumption that most Culex specimens were likely Cx. pipiens . All Psychodidae were members of the subfamily Psychodinae. Effect of application frequency on the abundance of mosquitoes and non-target species Analysis of the untreated control catch basins revealed clear seasonal patterns in dipteran abundance, with Culex spp. showing the highest activity (7.72 individuals/trap), followed by Chironomidae (1.36), Ae. albopictus (0.41) and Psychodidae (0.34). The peak activity for all taxonomic groups occurred around (ISO) calendar week 35 (Fig. 3 ). Intriguingly, Culex spp. exhibited a sharp peak followed by a rapid decline, whereas Ae. albopictus maintained low but stable numbers throughout the season, exceeding one individual only during calendar weeks 35 and 40 (Fig. 3 ). Larvicide treatments with VectoMax® FG substantially suppressed adult emergence compared with the untreated catch basins, with reductions most pronounced within 1 to 2 weeks post-application (Fig. 3 ). For Ae. albopictus , application frequencies of 2 to 6 weeks maintained low abundance (0.01–0.05 mosquitoes/trap), whereas frequencies of 8 and 10 weeks were less effective, particularly the 10-week interval, which closely resembled control levels. The model results (Eq. 1) indicated statistically significant suppression at application intervals of 6 weeks or shorter, with no significant associations observed for temperature or precipitation (Table 2 ). Compared with those of the control, Culex spp. trap counts were consistently lower across all application frequencies (Fig. 3 ). The GLMM results from Eq. 1 confirmed a significant negative association between all treatment intervals and Culex spp. abundance (Table 2 ). The effect of VectoMax® FG was also more pronounced on Culex spp. than on Ae. albopictus , indicating greater sensitivity to the larvicide. Additionally, temperature was positively associated with Culex spp. count, whereas precipitation was negatively associated with Culex spp. count (Table 2 ). In chironomids and psychodids, the model results (Eq. 1) indicate a significant decline in abundance at intervals of 4 weeks or shorter. Temperature had a statistically significant positive effect on chironomid abundance but a statistically significant negative effect on psychodids, whereas precipitation was not significantly associated with either group (Table 2 ). Table 2 Effects of VectoMax® FG application frequencies on the abundance of Aedes albopictus , Culex spp., Chironomidae and Psychodidae in catch basins Taxon Model predictor Coefficient 95% Confidence interval P -value Aedes albopictus Frequency (10 weeks) 1.07 0.31–3.68 n.s. Frequency (8 weeks) 0.47 0.13–1.72 n.s. Frequency (6 weeks) 0.16 0.04–0.64 0.010 Frequency (4 weeks) 0.11 0.03–0.49 0.004 Frequency (2 weeks) 0.02 0.00–0.17 < 0.001 Temperature (°C) 1.05 0.98–1.14 n.s. Precipitation (mm) 1 0.93 0.85–1.01 n.s. Culex spp. Frequency (10 weeks) 0.02 0.01–0.08 < 0.001 Frequency (8 weeks) 0.06 0.02–0.18 < 0.001 Frequency (6 weeks) 0.01 0.00–0.04 < 0.001 Frequency (4 weeks) 0.00 0.00–0.01 < 0.001 Frequency (2 weeks) 0.00 0.00–0.01 < 0.001 Temperature (°C) 1.20 1.10–1.30 < 0.001 Precipitation (mm) 1 0.92 0.85–0.99 0.024 Chironimidae Frequency (10 weeks) 0.59 0.21–1.63 n.s. Frequency (8 weeks) 0.39 0.14–1.12 n.s. Frequency (6 weeks) 0.37 0.13–1.04 n.s. Frequency (4 weeks) 0.19 0.07–0.57 0.002 Frequency (2 weeks) 0.06 0.02–0.19 < 0.001 Temperature (°C) 1.06 1.00–1.12 0.039 Precipitation (mm) 1 0.98 0.95–1.02 n.s. Psychodidae Frequency (10 weeks) 0.50 0.08–3.01 n.s. Frequency (8 weeks) 0.17 0.02–1.20 n.s. Frequency (6 weeks) 0.16 0.03–1.07 n.s. Frequency (4 weeks) 0.02 0.00–0.19 < 0.001 Frequency (2 weeks) 0.03 0.00–0.25 0.001 Temperature (°C) 0.85 0.76–0.96 0.01 Precipitation (mm) 1 0.96 0.92–1.01 n.s. 1 Precipitation with a lag of 1 week. 95% CI: 95% confidence interval. Estimates and 95% CIs are based on the GLMM in Eq. 1. Residual effect on adult insect abundance The model results (Eq. 2) on residual effects revealed significant non-linear effects of time since treatment across all the taxa (Fig. 4 ). Incorporating a random intercept for trap ID substantially improved model fit by accounting for consistent differences among traps, indicating that traps with higher mosquito counts in one week tended to have higher counts in subsequent weeks. Additionally, calendar time (days) was a good predictor of Ae. albopictus , Culex spp. and Chironomidae abundance, whereas no significant temporal trend was observed for Psychodidae abundance. Among the environmental covariates, one-week lagged precipitation and a 1°C increase above the mean temperature significantly influenced Chironomidae abundance, with temperature showing a positive association and precipitation showing a negative association (Additional file 1: Table S1 ). In contrast, only precipitation had a statistically significant negative effect on Ae. albopictus and Culex spp. abundance, whereas no significant associations were observed for Psychodidae. Suppression of both target and non-target taxa was most pronounced shortly after treatment, with predicted abundance reductions peaking during the first 19 days for Culex spp., 20 days for Ae. albopictus , 23 days for Chironomidae and 29 days for Psychodidae. Culex spp. showed sustained high suppression (> 80%) throughout this initial period, whereas Ae. albopictus remained above 80% suppression until day 36 and retained moderate efficacy (> 50%) up to day 46. Among the non-target taxa, Chironomidae experienced moderate reductions lasting through day 35, whereas Psychodidae showed sharper and more prolonged suppression, with reductions exceeding 80% up to day 34 and remaining moderate until day 45. Dose-response effects of application frequency on adult insect abundance In the continuous dose-response model (Eq. 3), the Ae. albopictus abundance was significantly influenced solely by application frequency, which was strongly negatively associated with the number of Ae. albopictus (Fig. 5 , Additional file 1: Table S2 ). Neither temperature nor lagged precipitation had a statistically significant effect. Model predictions indicate that reductions in Ae. albopictus abundance increased with more frequent applications, with a 73.9% reduction at the 8-week interval, which is currently implemented in several urban areas in Switzerland (pers. comm. Swiss Mosquito Network). According to the model prediction, suppression exceeds 80% at the 5-week interval, surpasses 90% with treatments every 4 weeks, and approaches near-complete control (99%) with biweekly applications. Additionally, variability in predicted abundance declined sharply with increasing treatment frequency, as reflected by narrowing 95% confidence intervals, suggesting a reduced risk of population resurgence. Marginal gains in reduction increased steadily up to the 4-week interval, peaking at 5.7%, before subsequently declining. In contrast, Culex spp. abundance was significantly affected by all three predictors. The application frequency has a strong negative effect; temperature is positively associated – each 1°C increase above the mean (19.6°C) significantly elevates counts – and precipitation lag exerts a smaller but significant negative effect (Fig. 5 , Additional file 1: Table S3). The predicted reductions in Culex spp. exceeds 80% – even at the 8-week application interval – and reaches over a 90% reduction with an application frequency every 4 weeks, and near-complete suppression at 2- to 3-week intervals. Like in Ae . albopictus , variability in abundance across catch basins declines as application frequency increases, although re-emergence fluctuations are less pronounced. Marginal gains peak at the 7-week interval (3.8%) and decrease rapidly at shorter application frequencies (Fig. 5 , Additional file 1: Table S3). For the non-target taxonomic groups, application frequency is also a significant predictor. Temperature has contrasting effects, with a positive relationship observed for Chironomidae abundance and a negative association for Psychodidae abundance. Precipitation lag was not a significant predictor for either group (Additional file 1: Table S3). The predicted reductions in non-target abundance increased with higher treatment frequency, with the abundance of Chironomidae being reduced by 43.6% at 10-week intervals and up to 94.3% under biweekly treatments. The degree of Psychodidae reduction ranged from 55.5% (10-week interval) to 98.3% (2-week interval). Marginal gains differed between taxa: Chironomidae gains increased steadily with shorter intervals, reaching a maximum of 9.2%, whereas Psychodidae gains peaked at a 6-week interval (6.6%) before diminishing at higher frequencies (Fig. 5 , Additional file 1: Table S3). Discussion This study demonstrated that the frequency of VectoMax® FG application is a critical factor for effectively controlling Ae. albopictus and Culex spp. in urban catch basins. While both taxa were significantly suppressed, Culex spp. responded consistently well across all the tested frequencies, indicating increased sensitivity to the larvicide. Application intervals longer than 5 weeks led to reduced efficacy and increased variability in mosquito counts, particularly for Ae. albopictus . Across both taxa, more frequent treatments resulted in narrower confidence intervals, indicating greater stability in population control. These findings support the manufacturer’s recommended 4-week interval and caution against extending application intervals beyond 5 weeks, especially in areas where Ae. albopictus is a primary concern. This study has several limitations to consider. The adult mosquito emergence traps used lacked protective covers, which may have allowed rainwater to flush out mosquitoes, potentially lowering catch numbers and complicating the assessment of precipitation effects. While the measurement error of these traps has not been fully quantified, a comparison of their seasonal trends with those of previous years revealed consistent patterns, supporting their effectiveness for temporal monitoring [ 31 , 32 ]. However, the limited research on species-specific mosquito dynamics in Switzerland highlights the need for more targeted surveillance to refine local vector control strategies. Microclimatic conditions within catch basins – such as temperature, humidity, and water retention – were not continuously monitored, limiting our understanding of how basin-specific environmental variability may influence larvicide persistence or mosquito emergence. This is particularly relevant for Ae. albopictus , which remained active until late October, suggesting that thermal buffering within catch basins may have extended its breeding season [ 33 ]. Furthermore, although the biological response to larvicide application frequency is inherently non-linear, we adopted a linear representation to provide a simplified and practical framework for operational guidance. This trade-off balances model complexity with clarity, offering control programmes a more straightforward decision-making tool. Finally, as this study was conducted within a single urban region, caution should be exercised in generalising the findings to areas with different climatic, infrastructural or ecological characteristics. Bacillus thuringiensis var. israelensis and L. sphaericus are key components of environmentally sustainable vector control programmes, which are valued for their high specificity toward mosquito larvae and minimal toxicity to vertebrates and most non-target organisms. These microbial larvicides act through parasporal crystal protoxins that, upon ingestion, are solubilised and activated in the alkaline midgut of mosquito larvae. The activated toxins bind to specific receptors on midgut epithelial cells, leading to pore formation, cell lysis and larval death. Bacillus thuringiensis var. israelensis is known for its rapid action but limited environmental persistence, typically requiring reapplication within two to four weeks [ 34 ]. In contrast, L. sphaericus exhibits longer-lasting efficacy, owing to its ability to reproduce within the cadavers of affected insect larvae, thereby sustaining its larvicidal activity through recycling. When used in combination, Bti and L. sphaericus are intended to provide both immediate and prolonged mosquito control [ 35 ]. Indeed, the dual-action formulation of VectoMax® FG – which combines Bti for rapid knockdown with L. sphaericus for residual activity – appears to provide a synergistic benefit [ 36 ]. Nonetheless, the progressive decline in efficacy beyond 3 to 5 weeks post-treatment suggests that the residual component alone is insufficient for sustained suppression of species such as Ae. albopictus , underscoring the need for timely reapplications. The results highlight the importance of tailoring larvicide application intervals to species-specific biology. The higher sensitivity of Culex spp. may reflect ecological and physiological traits, such as slower feeding rates, habitat preferences and increased susceptibility to L. sphaericus components of the larvicide [ 37 , 38 ]. Previous studies support these patterns; for example, competitive interactions under limited food conditions have shown that Aedes aegypti can outcompete Cx. quinquefasciatus , potentially explaining some of the observed differences in control efficacy [ 39 ]. Comparisons with previous studies confirm the general pattern of residual activity following VectoMax® FG application but also highlight notable variability across different ecological settings. For example, a semi-field trial conducted in Brazil demonstrated the suppression of Ae. albopictus for up to eight weeks and Culex spp. for nine weeks using a similar larvicide formulation [ 21 ]. Similarly, a field study in Ticino, Switzerland, reported reductions of approximately 60% in Ae. albopictus and up to 85% in Culex spp. within five to ten weeks post-application [ 20 ]. These findings are broadly consistent with our results; however, our data suggest a need for more frequent reapplications to sustain high control levels, particularly for Ae. albopictus , potentially reflecting local environmental factors. One study documented the efficacy of VectoMax® FG in challenging field conditions, including vegetated environments with high organic content, where residual effects against Culex spp. persisted for up to 36 days [ 35 ]. Laboratory studies under controlled conditions have reported even longer durations of efficacy, although often at application rates substantially exceeding field recommendations. For example, one study using 57.7 g/m² VectoMax® FG in catch basin analogues reported complete suppression for up to one year [ 40 ], whereas other laboratory experiments achieved > 80% control of Ae. aegypti for over 23 weeks with elevated Bti concentrations [ 41 ]. These extended durations are unlikely to be replicated under field conditions because of the environmental degradation of active ingredients. As seen in the present study, susceptibility patterns among target species further complicate efficacy outcomes. Culex quinquefasciatus and Anopheles gambiae exhibit comparable reduction rates during the first nine days following treatment with Bti or L. sphaericus [ 42 ]. In contrast, Ae. aegypti has notably lower susceptibility to L. sphaericus , with minimal reductions observed at practical dosages, whereas Ae. albopictus appears moderately susceptible [ 43 ]. In addition to efficacy, ecological safety remains a cornerstone of integrated mosquito management strategies. Despite their generally high specificity, larvicide treatments can have unintended ecological effects on non-target dipteran taxa such as chironomids and psychodids. These taxa play critical roles in the decomposition of organic matter and nutrient cycling in aquatic ecosystems, particularly in polluted or eutrophic habitats such as urban catch basins. Disruption of these communities may have cascading effects on higher trophic levels and alter ecosystem functioning [ 34 , 44 , 45 ]. The Ticino study reported a 50% reduction in chironomid populations seven weeks after Bti application [ 20 ], a pattern found in our findings and in others, such as a semi-field trial in Germany, which reported chironomid reductions ranging from 39–68% [ 44 ]. While these reductions indicate some non-target effects, their magnitude remains substantially lower than that observed for mosquito larvae, supporting the selective action of bacterial larvicides. Furthermore, a field study in Cameroon found no significant changes in zooplankton or macroinvertebrate diversity or abundance following VectoMax® FG application, reinforcing its ecological compatibility when used according to guidelines [ 46 ]. Similarly, other studies have reported minimal effects of Bti on aquatic nutrient dynamics and no measurable impacts on riparian spider populations, suggesting limited disruption to broader ecosystem functions [ 47 ]. Our findings reinforce the importance of following the label instructions provided by the manufacturer when applying VectoMax FG. Balancing effective mosquito suppression with ecological considerations – particularly with respect to non-target impacts – requires careful calibration of treatment schedules to optimise both vector control and environmental stewardship. Future studies should aim to better understand the influence of environmental factors – particularly rainfall – on mosquito catch data by employing traps equipped with rain shields and by directly measuring water levels within catch basins. In addition, incorporating continuous microclimate monitoring, including temperature and humidity sensors, would offer valuable insights into site-specific conditions that may influence larvicide persistence and mosquito emergence. This is especially relevant for Ae. albopictus , which remained active through late October in our study area, indicating a potential shift in seasonal emergence patterns likely driven by thermal buffering within urban catch basins. A more detailed understanding of these microclimatic dynamics could inform the timing and frequency of larvicide applications and help ensure more reliable seasonal coverage. Conclusion Our findings indicate that the reapplication of VectoMax® FG at 5-week intervals is necessary to achieve effective suppression of both Ae. albopictus and Culex spp. While Culex spp. showed robust sensitivity even at extended intervals, Ae. albopictus required more frequent treatments to prevent population rebound. The application frequency influenced not only the suppression level but also the variability in mosquito abundance, contributing to more stable vector control. These results support the integration of optimised treatment intervals into mosquito management programmes while emphasising the need for localised adjustments on the basis of ecological conditions and operational feasibility. Abbreviations Ae. Aedes Bti Bacillus thuringiensis var. israelensis Cx. Culex FG Fine granule LDPE Low-density polyethylene foam Declarations Acknowledgement We would like to thank Eren Kahraman, Elena Spörri, Svenja Zehnder and Giulian Meier for their help during the fieldwork. Many thanks also to Oscar Anido, Frank Bluess and Till Koeppel from the civil engineering office (‘Tiefbauamt’) of the Canton of Basel-Stadt for their expertise and help with equipment, information about the catch basin system and their help whenever problems occurred. Furthermore, we would like to thank Valentina Campana and Eleonora Flacio from the University of Applied Sciences and Arts of Southern Switzerland (SUPSI) for sharing their expertise in designing the emergence traps. Finally, we thank Hans Bossler, Susanne Biebinger and Ann-Christin Honnen from the Cantonal Laboratory Basel-Stadt for facilitating and supporting the project. Funding The study received funding from the Cantonal Laboratory Basel-Stadt (KLBS), Switzerland. Availability of data and materials The dataset supporting the conclusions of this article is included in Additional file 2. Author contributions PM, BM, and TAS conceptualised and designed the study. TK and TAS were responsible for data processing. TK conducted all the analyses; prepared the results, figures and supplementary materials; and drafted the initial manuscript. PM, BM and TAS contributed to critical review and interpretation of the findings. TK and PM finalised and edited the manuscript. All authors reviewed and approved the final version. Ethics approval and consent to participate Not applicable Consent for publication Not applicable Competing interests Not applicable References Medlock JM, Hansford KM, Schaffner F, Versteirt V, Hendrickx G, Zeller H, et al. A review of the invasive mosquitoes in Europe: ecology, public health risks, and control options. Vector Borne Zoonotic Dis. 2012;12(6):435–47. Oliveira S, Rocha J, Sousa CA, Capinha C. Wide and increasing suitability for Aedes albopictus in Europe is congruent across distribution models. Sci Rep. 2021;11(1). Gossner CM, Ducheyne E, Schaffner F. Increased risk for autochthonous vector-borne infections transmitted by Aedes albopictus in continental Europe. Euro Surveill. 2018;23(24). Brem J, Elankeswaran B, Erne D, Hedrich N, Lovey T, Marzetta V, et al. Dengue “homegrown” in Europe (2022 to 2023). New Microbes New Infect. 2023;56. de Wispelaere M, Desprès P, Choumet V. European Aedes albopictus and Culex pipiens are competent vectors for Japanese encephalitis virus. PLoS Negl Trop Dis. 2017;11(1). Richards SL, Anderson SL, Lord CC, Smartt CT, Tabachnick WJ. Relationships between infection, dissemination, and transmission of West Nile virus RNA in Culex pipiens quinquefasciatus (Diptera: Culicidae). J Med Entomol. 2012;49(1):132–42. Diaz LA, Flores FS, Beranek M, Rivarola ME, Almirón WR, Contigiani MS. Transmission of endemic St Louis encephalitis virus strains by local Culex quinquefasciatus populations in Cordoba, Argentina. Trans R Soc Trop Med Hyg 2013;107(5):332–4. Scheuch DE, Schäfer M, Eiden M, Heym EC, Ziegler U, Walther D, et al. Detection of Usutu, Sindbis, and Batai viruses in mosquitoes (Diptera: Culicidae ) collected in Germany, 2011–2016. Viruses. 2018;10(7). Vloet RP, Vogels CB, Koenraadt CJ, Pijlman GP, Eiden M, Gonzales JL, et al. Transmission of Rift Valley fever virus from European-breed lambs to Culex pipiens mosquitoes. PLoS NTDs. 2017;11(12). Ferraguti M, Heesterbeek H, Martínez-de la Puente J, Jiménez‐Clavero MÁ, Vázquez A, Ruiz S, et al. The role of different Culex mosquito species in the transmission of West Nile virus and avian malaria parasites in Mediterranean areas. Transbound Emerg Dis. 2021;68(2):920–30. Nchoutpouen E, Talipouo A, Djiappi-Tchamen B, Djamouko-Djonkam L, Kopya E, Ngadjeu CS, et al. Culex species diversity, susceptibility to insecticides and role as potential vector of Lymphatic filariasis in the city of Yaoundé, Cameroon. PLoS Negl Trop Dis. 2019;13(4). Rydzanicz K, Jawień P, Lonc E, Modelska M. Assessment of productivity of Culex spp. larvae (Diptera: Culicidae ) in urban storm water catch basin system in Wrocław (SW Poland). Parasitol Res. 2016;115:1711–20. Marcolin L, Zardini A, Longo E, Caputo B, Poletti P, Di Marco M. Mapping the habitat suitability of Culex pipiens in Europe using ensemble bioclimatic modelling. bioRxiv. 2025. Brugman VA, Hernández-Triana LM, Medlock JM, Fooks AR, Carpenter S, Johnson N. The role of Culex pipiens L.(Diptera: Culicidae ) in virus transmission in Europe. Int J Environ Health Res. 2018;15(2):389. Flacio E, Lüthy P, Patocchi N, Guidotti F, Tonolla M, Peduzzi R. Primo ritrovamento di Aedes albopictus in Svizzera. Boll Della Soc Ticinese Sci Nat. 2004;92:141–2. Müller P, Engeler L, Vavassori L, Suter T, Guidi V, Gschwind M, et al. Surveillance of invasive Aedes mosquitoes along Swiss traffic axes reveals different dispersal modes for Aedes albopictus and Ae. japonicus . PLoS Negl Trop Dis. 2020;14(9). Bellini R, Michaelakis A, Petrić D, Schaffner F, Alten B, Angelini P, et al. Practical management plan for invasive mosquito species in Europe: I. Asian tiger mosquito ( Aedes albopictus ). Trop Med Infect Dis. 2020;35. Ravasi D, Parrondo Monton D, Tanadini M, Flacio E. Effectiveness of integrated Aedes albopictus management in southern Switzerland. Parasit vectors. 2021;14:1–15. Flacio E, Engeler L, Tonolla M, Lüthy P, Patocchi N. Strategies of a thirteen year surveillance programme on Aedes albopictus (Stegomyia albopicta) in southern Switzerland. Parasit Vectors. 2015;8:1–18. Ravasi D, Monton DP, Tanadini M, Campana V, Flacio E. Efficacy of biological larvicide VectoMax® FG against Aedes albopictus and Culex pipiens under field conditions in urban catch basins. J Eur Mosq Control Assoc. 2023;42(1):51–60. Rique HL, Menezes HSG, Melo-Santos MAV, Silva-Filha MHNL. Evaluation of a long-lasting microbial larvicide against Culex quinquefasciatus and Aedes aegypti under laboratory and a semi-field trial. Parasit Vectors. 2024;17(1):391. Biebinger S, A-C H. Asiatische Tigermücke - Überwachung und Bekämpfung im Kanton Basel-Stadt 2023. Basel, Kant Lab, Gesundheitsdep Kt Basel-Stadt. 2024:5. Briët O; Lindström A ED, Hul N, Braks M, Petrić D, Schaffner F. 'Reverse' identification key for mosquito species. 2021. Buck M, Woodley NE, Borkent A, Wood DM, Pape T, Vockeroth JR, et al. Key to Diptera families-adults2009. 95–156 p. Marshall A, Kirk-Spriggs H, Muller S, Paiero M, Yau T, Jackson D. Key to Diptera families-adults 122016. 1–81 p. ODK Core Team. Get ODK Inc., San Diego, CA, USA; 2024. R Core Team. R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna, Austria; 2025. Canty A RB. boot: Bootstrap R (S-Plus) Functions. R package version 1.3–31. ed2024. Brooks ME, Kristensen K, van Benthem KJ, Magnusson A, Berg CW, Nielsen A, et al. glmmTMB balances speed and flexibility among packages for zero-inflated generalized linear mixed modeling. R J. 2017; 9(2):378–400. SN. W. Generalized Additive Models: An Introduction with R. 2 ed. Boca Raton: Chapman and Hall/CRC; 2017. Schaffner F, Mathis A. Spatio-temporal diversity of the mosquito fauna (Diptera: Culicidae ) in Switzerland. 2013. Flacio E, Engeler L, Tonolla M, Müller P. Spread and establishment of Aedes albopictus in southern Switzerland between 2003 and 2014: an analysis of oviposition data and weather conditions. Parasit Vectors. 2016;9:1–14. Ravasi D, Mangili F, Huber D, Cannata M, Strigaro D, Flacio E. The effects of microclimatic winter conditions in urban areas on the risk of establishment for Aedes albopictus . Sci Rep. 2022;12(1):15967. Silva-Filha MHNL, Romão TP, Rezende TMT, Carvalho KdS, Gouveia de Menezes HS, Alexandre do Nascimento N, et al. Bacterial toxins active against mosquitoes: Mode of action and resistance. Toxins. 2021;13(8):523. Virgillito C, Manica M, Marini G, Rosà R, Della Torre A, Martini S, et al. Evaluation of Bacillus thuringiensis subsp. israelensis and Bacillus sphaericus combination against Culex pipiens in highly vegetated ditches. J Am Mosq Control Assoc. 2022;38(1):40–5. Boyce R, Lenhart A, Kroeger A, Velayudhan R, Roberts B, Horstick O. Bacillus thuringiensis israelensis ( Bti ) for the control of dengue vectors: systematic literature review. Trop Med Int Health. 2013;18(5):564–77. Lacey LA. Bacillus thuringiensis serovariety israelensis and Bacillus sphaericus for mosquito control. J Am Mosq Control Assoc. 2007;23(sp2):133–63. McMillan JR, Olson MM, Petruff T, Shepard JJ, Armstrong PM. Impacts of Lysinibacillus sphaericus on mosquito larval community composition and larval competition between Culex pipiens and Aedes albopictus . Sci Rep. 2022;12(1). Santana-Martínez JC, Molina J, Dussán J. Asymmetrical competition between Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae ) coexisting in breeding sites. Insects. 2017;8(4):111. Eritja R. Laboratory tests on the efficacy of VBC60035, a combined larvicidal formulation of Bacillus thuringiensis israelensis (strain AM65-52) and Bacillus sphaericus (strain 2362) against Aedes albopictus in simulated catch basins. J Am Mosq Control Assoc. 2013;29(3):280–3. Ritchie SA, Rapley LP, Benjamin S. Bacillus thuringiensis var. israelensis ( Bti ) provides residual control of Aedes aegypti in small containers. Am J Trop Med Hyg. 2010;82(6):1053. Derua YA, Tungu PK, Malima RC, Mwingira V, Kimambo AG, Batengana BM, et al. Laboratory and semi-field evaluation of the efficacy of Bacillus thuringiensis var. israelensis (Bactivec®) and Bacillus sphaericus (Griselesf®) for control of mosquito vectors in northeastern Tanzania. Curr Res Parasitol Vector-Borne Dis. 2022;2. Suter T, Crespo MM, de Oliveira MF, de Oliveira TSA, de Melo-Santos MAV, de Oliveira CMF, et al. Insecticide susceptibility of Aedes albopictus and Ae. aegypti from Brazil and the Swiss-Italian border region. Parasit Vectors. 2017;10:1–11. Allgeier S, Kästel A, Brühl CA. Adverse effects of mosquito control using Bacillus thuringiensis var. israelensis : Reduced chironomid abundances in mesocosm, semi-field and field studies. Ecotoxicol Environ Saf. 2019;169:786–96. Poulin B. Indirect effects of bioinsecticides on the nontarget fauna: the Camargue experiment calls for future research. Acta Oecol. 2012;44:28–32. Thierry D-N, Djamouko-Djonkam L, Gisèle FD, Audrey MMP, Timoléon T, Hubert Z-TS, et al. Assessment of the impact of the biological larvicide VectoMax G: Combination of Bacillus thuringiensis and Lysinibacillus sphaericus on non-target aquatic organisms in Yaoundé-Cameroon. Heliyon. 2023;9(8). Kolbenschlag S, Bollinger E, Gerstle V, Brühl CA, Entling MH, Schulz R, et al. Impact across ecosystem boundaries–Does Bti application change quality and composition of the diet of riparian spiders? Sci Total Environ. 2023;873. Additional Declarations No competing interests reported. Supplementary Files Kirrmannetal.Additionalfile1.docx Kirrmannetal.Additionalfile2.xlsx Cite Share Download PDF Status: Published Journal Publication published 27 Nov, 2025 Read the published version in Parasites & Vectors → Version 1 posted Editorial decision: Revision requested 06 Oct, 2025 Reviews received at journal 06 Oct, 2025 Reviews received at journal 24 Sep, 2025 Reviewers agreed at journal 23 Sep, 2025 Reviewers agreed at journal 21 Sep, 2025 Reviewers invited by journal 25 Aug, 2025 Editor assigned by journal 30 Jul, 2025 Submission checks completed at journal 30 Jul, 2025 First submitted to journal 29 Jul, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7241349","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":505318765,"identity":"2181a909-80f2-421e-bc03-110b51b01735","order_by":0,"name":"Tim Kirrmann","email":"","orcid":"","institution":"Swiss Tropical and Public Health Institute","correspondingAuthor":false,"prefix":"","firstName":"Tim","middleName":"","lastName":"Kirrmann","suffix":""},{"id":505318766,"identity":"bb58a70b-31d2-4313-bfcb-9b6578206b34","order_by":1,"name":"Thomas A. Smith","email":"","orcid":"","institution":"Swiss Tropical and Public Health Institute","correspondingAuthor":false,"prefix":"","firstName":"Thomas","middleName":"A.","lastName":"Smith","suffix":""},{"id":505318767,"identity":"a1162171-05bd-47a5-bd56-058038761aca","order_by":2,"name":"Bianca Modespacher","email":"","orcid":"","institution":"Swiss Tropical and Public Health Institute","correspondingAuthor":false,"prefix":"","firstName":"Bianca","middleName":"","lastName":"Modespacher","suffix":""},{"id":505318768,"identity":"2692456c-176a-47ee-bfe6-479e029332b6","order_by":3,"name":"Pie Müller","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABAElEQVRIiWNgGAWjYDACZgglw8fAwPiAgUECxGED4gMEtfAAlTEbgLWwEdLCgNDCBraCoBZzduYDTDfbbHjY2HufVf5ss7CXn9977AFDzR2cWiyb2RKYc9vSeNh4jpvd5m2TSNxwjC/dgOHYM5xaDA7zGAC1HOZhk0hju824TSLBgI3HTIKx4TAeLfwfgFr+87DJP2Mr/LlNwl6+jaAWHgaglgNAW9jYGHi3ARUfI6AF6BeDwznnkoF+SWOW5v0H8ktemkTCMdxazPkPP3ycU2Ynx89+jPHjjzN19vLNZ49JfKjB4zAGzCjgYWBIwKkBogUd8OBRPwpGwSgYBSMRAABS2Ug0eXGQcwAAAABJRU5ErkJggg==","orcid":"","institution":"Swiss Tropical and Public Health Institute","correspondingAuthor":true,"prefix":"","firstName":"Pie","middleName":"","lastName":"Müller","suffix":""}],"badges":[],"createdAt":"2025-07-29 09:08:42","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7241349/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7241349/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s13071-025-07169-0","type":"published","date":"2025-11-27T15:57:26+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":90403537,"identity":"82770515-3889-43b6-942c-330cf428693b","added_by":"auto","created_at":"2025-09-02 10:42:51","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":774603,"visible":true,"origin":"","legend":"\u003cp\u003eMap of catch basins included in the study in the St. Johann district, Basel, Switzerland. Each point represents a catch basin, and the colour indicates the respective larvicide application frequency (treatment). From a list of 768 catch basins located at St. Johan, 30 were randomly assigned to each of the 6 treatments (i.e. a total of 180 catch basins). The black line indicates the district border of St. Johann, Basel. The map was created in QGIS version 3.43.13, incorporating a base layer from OpenStreetMap (© OpenStreetMap contributors).\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-7241349/v1/7dfe45a9fcafbca2917a7bf1.png"},{"id":90403538,"identity":"4e387e9e-6b54-4e1f-98ae-189d4acf51c8","added_by":"auto","created_at":"2025-09-02 10:42:51","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":376371,"visible":true,"origin":"","legend":"\u003cp\u003eAdult emergence trap installed in a catch basin to assess the effectiveness and optimal reapplication interval of larvicide treatments. The trap captures emerging adult mosquitoes, providing direct evidence of larval survival following treatment.\u003c/p\u003e","description":"","filename":"image2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7241349/v1/01faafd0911c0616f7f0baec.jpeg"},{"id":90403545,"identity":"af6246e1-acf6-431e-b199-7f3fb9a547f2","added_by":"auto","created_at":"2025-09-02 10:42:51","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":692053,"visible":true,"origin":"","legend":"\u003cp\u003eAbundance of mosquitoes and non-target insects in untreated and treated catch basins. Each point represents the arithmetic mean count per trap and ISO calendar week for the four taxonomic groups. The whiskers represent the 95% confidence intervals around the mean count. Owing to illness no sampling was executed in week 39.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-7241349/v1/a68ed17bae35f870d5b8bdd7.png"},{"id":90403539,"identity":"89f6ffe0-3c66-49f2-8a0b-ecb539de04ed","added_by":"auto","created_at":"2025-09-02 10:42:51","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":565896,"visible":true,"origin":"","legend":"\u003cp\u003eResidual effects of VectoMax® FG in catch basins against mosquitoes and non-target insects. Each point represents the estimated mean number of adult insects per trap and days post treatment, with whiskers representing the 95% confidence interval around the means. The lines show the predicted abundance as a function of time post treatment estimated from GAMMs (Equation 2). The shaded areas show the 95% confidence ranges around the predicted lines.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-7241349/v1/2317a0cc7401b7ef8c9225d5.png"},{"id":90404898,"identity":"be5b362a-3668-4e4e-8f88-694192494514","added_by":"auto","created_at":"2025-09-02 10:58:51","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":685793,"visible":true,"origin":"","legend":"\u003cp\u003ePercent reduction in mosquito and non-target insect abundance as compared with that in the control group as a function of VectoMax® FG treatment application frequency. The predictions are based on the fitted GLMM (Equation 3), allowing exploration across intermediate treatment intervals. Specific values for treatment intervals from 2 to 10 weeks are given in Additional file 1 (Table S2).\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-7241349/v1/728b8edb443eb9281cbe8d89.png"},{"id":97178344,"identity":"b6ac937f-41b7-4a56-a8f1-e758794659f6","added_by":"auto","created_at":"2025-12-01 16:08:33","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3700741,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7241349/v1/cf616cfc-f8e9-48ca-9f5f-42a5810e7fd5.pdf"},{"id":90403540,"identity":"52de9a49-5a2b-4c2d-9006-8fe16da8a56a","added_by":"auto","created_at":"2025-09-02 10:42:51","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":230993,"visible":true,"origin":"","legend":"","description":"","filename":"Kirrmannetal.Additionalfile1.docx","url":"https://assets-eu.researchsquare.com/files/rs-7241349/v1/2eea0cdadca75adabb63f11a.docx"},{"id":90403576,"identity":"23fe8a84-96d0-4385-a14b-3a1df60f5c18","added_by":"auto","created_at":"2025-09-02 10:42:52","extension":"xlsx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":30067748,"visible":true,"origin":"","legend":"","description":"","filename":"Kirrmannetal.Additionalfile2.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-7241349/v1/51bf574f849b6db330eb9045.xlsx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Optimising the application frequency of VectoMax® FG for the control of Ae. albopictus and Culex spp. in the urban environment: findings from a randomised controlled trial","fulltext":[{"header":"Background","content":"\u003cp\u003eClimate projections indicate a continued expansion of the range suitable for \u003cem\u003eAe. albopictus\u003c/em\u003e in Europe, raising significant public health concerns due to its competence as a vector for more than 20 arboviruses, including dengue, chikungunya and Zika [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. \u003cem\u003eAedes albopictus\u003c/em\u003e has already been associated with multiple chikungunya outbreaks in Italy and France [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] and increasing autochthonous dengue outbreaks in Europe. These findings underscore the urgent need for effective mosquito control measures in areas infested with \u003cem\u003eAe. albopictus\u003c/em\u003e [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eLike \u003cem\u003eAe. albopictus, Culex\u003c/em\u003e spp. have the potential to transmit viruses, including Japanese encephalitis virus (JEV) [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], West Nile virus (WNV) [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e] and several other arboviruses [\u003cspan additionalcitationids=\"CR8 CR9\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], as well as filarial parasites [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. The ecological success of \u003cem\u003eCulex\u003c/em\u003e spp. in urban settings is largely driven by the availability of organic-rich water bodies [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Consequently, JEV, WNV, Usutu virus (USUV) and Sindbis virus (SINV) have been found in the European \u003cem\u003eCulex\u003c/em\u003e population in urban environments, indicating the importance of \u003cem\u003eCulex\u003c/em\u003e spp. control measures [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eSince its first detection in 2003 [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], \u003cem\u003eAe. albopictus\u003c/em\u003e has also become well established in Switzerland, spreading particularly along major transportation corridors [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. In urban settings, mosquito control strategies typically involve a combination of public awareness campaigns to avoid potential breeding sites and larviciding of permanent water bodies such as catch basins [\u003cspan additionalcitationids=\"CR18\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. In Switzerland, VectoMax\u0026reg; FG \u0026ndash; a larvicide that combines \u003cem\u003eBacillus thuringiensis\u003c/em\u003e var. \u003cem\u003eisraelensis\u003c/em\u003e (\u003cem\u003eBti\u003c/em\u003e) and \u003cem\u003eLysinibacillus sphaericus\u003c/em\u003e \u0026ndash; is routinely used in public mosquito control programs [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. While the manufacturer recommends reapplication every 4 weeks, emerging evidence suggests that longer intervals may still provide effective control and enhance cost-efficiency [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Laboratory studies have shown that formulations combining \u003cem\u003eBti\u003c/em\u003e and \u003cem\u003eL. sphaericus\u003c/em\u003e, such as VectoMax\u0026reg; FG, can achieve greater than 80% reduction in both \u003cem\u003eCulex quinquefasciatus\u003c/em\u003e and \u003cem\u003eAedes aegypti\u003c/em\u003e populations for up to 8 weeks. This extended efficacy is largely attributed to the synergistic action of the Cyt1Aa toxin in \u003cem\u003eBti\u003c/em\u003e, which facilitates the entry of Bin toxins into the epithelial cells of larvae that are resistant or lack Bin receptors [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eTo evaluate the effect of VectoMax\u0026reg; FG application frequency on reducing the number of adult mosquitoes, we conducted a randomised controlled trial (RCT) in the St. Johann district in Basel, Switzerland, during the 2024 mosquito season. Catch basins were treated at different frequencies, ranging from 2- to 10-week intervals, and their effects on mosquito abundance were measured via adult emergence traps placed in the catch basins.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cb\u003eStudy area\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe St. Johann district, located in the north-west of the city of Basel, Switzerland, was selected for the trial because of its well-documented high prevalence of \u003cem\u003eAe. albopictus\u003c/em\u003e and its strategic importance as the initial point of entry of the species into Basel [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Basel is highly urbanised with dense residential infrastructure and many underground catch basins that provide ideal conditions for container-breeding mosquitoes.\u003c/p\u003e\u003cp\u003e\u003cb\u003eWeather data\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe daily mean air temperature and total precipitation were obtained from the nearest MeteoSwiss stations \u0026ndash; Basel-St. Johann (temperature at 2 m above ground) and Basel-Binningen (precipitation).\u003c/p\u003e\u003cp\u003e\u003cb\u003eTreatment procedure\u003c/b\u003e\u003c/p\u003e\u003cp\u003eFrom a list of 768 catch basins in St. Johann, provided by the local administration, 30 were randomly assigned to each of five larvicide application frequencies \u0026ndash; 2, 4, 6, 8 or 10 weeks \u0026ndash; or to a negative control group that received no treatment (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Each treatment consisted of VectoMax\u0026reg; FG (Valent BioSciences, Libertyville, IL, USA) combining \u003cem\u003eBti\u003c/em\u003e (strain AM65-52) and \u003cem\u003eLysinobacillus sphaericus\u003c/em\u003e (strain ABTS 1743) at a dose of 10 g per catch basin, following the city of Basel\u0026rsquo;s standard procedure. A pre-measured 10 g cup was used to dispense the granules into each catch basin through a funnel to minimise spillage. Treatments commenced on 29 April and continued until 24 October 2024. During that period, catch basins treated at frequencies of 2, 4, 6, 8 and 10 weeks received 13, six, four, three and two treatments, respectively.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eMosquito collection procedure\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe emergence of adult mosquitoes, and other dipterans, from the selected catch basins was monitored weekly via custom-built adult emergence traps on the basis of the design of Ravasi et al. [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Each trap consisted of a white plastic funnel with a diameter of 16.1 cm. Low-density polyethylene foam (LDPE) was attached around the base to allow the traps to float on the water, resulting in a total diameter of 20.5 cm. The openings of the funnels were 1.7 cm wide and led directly into collection cups, measuring 9.1 cm in diameter and 10.1 cm in height. Each cup had a 5.1 cm opening at the base covered with a fine mesh net. Fine mesh nets with small openings were also attached to the tops of the cups, allowing mosquitoes to enter through the funnel while preventing their escape during cup removal and replacement. Traps were placed inside the catch basins, floating on the water surface to capture emerging adult dipterans. To ensure stability, three 10 cm LDPE foam pieces were attached to the base of each trap (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Traps were removed and replaced on a weekly basis, during which their functionality \u0026ndash; including net integrity and placement \u0026ndash; was checked, alongside catch basin conditions such as water level and the presence of leaves or other debris.\u003c/p\u003e\u003cp\u003eEach cup was labelled with the corresponding catch basin ID and the week of collection to ensure traceability of the samples. Mosquitoes were brought to the laboratory and frozen at -18\u0026deg;C for at least 2 hours. The samples were then transferred into 1.5 ml Eppendorf tubes in pools of up to 10 individuals and stored at -18\u0026deg;C until later identification.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eMosquito identification\u003c/b\u003e\u003c/p\u003e\u003cp\u003eAt the conclusion of the field season, all frozen insects were identified morphologically to major taxonomic groups under a stereo microscope, using the \u0026lsquo;Reverse identification key for mosquito species\u0026rsquo; by the ECDC and the \u0026lsquo;Key to Diptera families \u0026ndash; adults\u0026rsquo; [\u003cspan additionalcitationids=\"CR24\" citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The taxonomic groups included \u003cem\u003eCulex\u003c/em\u003e spp., \u003cem\u003eChironomidae\u003c/em\u003e, \u003cem\u003ePsychodidae\u003c/em\u003e and \u003cem\u003eAedes\u003c/em\u003e spp. Specimens belonging to the genus \u003cem\u003eAedes\u003c/em\u003e were further identified to the species level.\u003c/p\u003e\u003cdiv id=\"Sec2\" class=\"Section2\"\u003e\u003ch2\u003eData analysis\u003c/h2\u003e\u003cp\u003eThe data were first recorded on paper forms and then transferred to an Open Data Kit database [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Subsequent data analysis was performed in R version 4.51 [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], including data on the four taxonomic groups \u003cem\u003eAe. albopictus\u003c/em\u003e, \u003cem\u003eCulex\u003c/em\u003e spp., Chironomidae and Psychodidae.\u003c/p\u003e\u003cp\u003eAbundance was summarised as the arithmetic mean number of specimens per taxonomic group and per adult emergence trap per week, with 95% confidence intervals (CIs) estimated using the R package \u0026lsquo;boot\u0026rsquo; [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], on the basis of 1,000 bootstrap samples. This approach allowed for the estimation of 95% CIs without requiring preliminary assumptions regarding the distribution, thereby providing CIs that more reliably reflect the observed data.\u003c/p\u003e\u003cp\u003eTo evaluate the effects of larvicide application frequency, temperature and precipitation on mosquito abundance, generalised linear mixed models (GLMMs) and generalised additive mixed models (GAMMs) were developed, using the R packages \u0026lsquo;glmmTMB\u0026rsquo; [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e] and \u0026rsquo;mgcv\u0026rsquo; [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] respectively. For the models, the temperature was centered around the mean of 19.7\u0026deg;C. To account for potential delays between weather conditions and changes in mosquito abundance several lag periods (0 to 21 days) for both temperature and precipitation were assessed. Based on biological plausibility and preliminary model performance, only a 1-week lag for precipitation was selected for the final models. Owing to overdispersion in the mosquito count data, models were fitted via a negative binomial error distribution, and separate models were constructed for each taxonomic group to account for taxon-specific responses.\u003c/p\u003e\u003cp\u003eFirst, a GLMM with categorical application frequency was used to quantify the associations between application frequency, temperature and lagged precipitation while accounting for temporal and spatial correlation through random intercepts (Eq.\u0026nbsp;1). Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e explains the different variables and model terms used in the statistical models described above.\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}{\\nu\\:}_{i}\\in\\:0.1,\\:0.125,\\:0.167,\\:0.2,\\:0.5\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\\\\\:{log}\\left(E\\left[{Y}_{i}\\right]\\right)=\\:{\\beta\\:}_{0}\\:+\\:\\sum\\:_{j=1}^{5}{\\beta\\:}_{j}1\\left({\\nu\\:}_{i}=j\\right)+\\:{\\beta\\:}_{7}\\tau\\:ᵢ\\:+\\:{\\beta\\:}_{8}\\rho\\:\\:+\\:{\\mu\\:}_{1}\\left[i\\right]+\\:{\\mu\\:}_{2}\\left[i\\right]\\#\\left(1\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eNext, the observed mean trap counts with 95% confidence intervals were plotted to illustrate the relationship between mosquito abundance and time since the most recent treatment. To better understand these trends, model-based estimates of mean trap counts generated from GAMMs were overlaid. To establish a baseline for comparison, initial mosquito abundance was estimated by setting the \u0026lsquo;time since treatment\u0026rsquo; to zero in untreated control catch basins. Although equivalent GLMMs using the same predictors yielded lower Akaike information criterion (AIC) values, diagnostic checks revealed consistent nonlinear patterns in abundance over time across all taxa. Therefore, GAMMs were selected for their greater flexibility in capturing these dynamics (Eq.\u0026nbsp;2).\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}{log}\\left({\\eta\\:}_{i}\\right)=\\:f\\left({t}_{i}\\right)+\\:{\\beta\\:}_{2}\\tau\\:ᵢ+\\:{\\beta\\:}_{3}{\\rho\\:}_{i}\\:+\\:{b}_{1}\\left[i\\right]\\:+\\:{b}_{2}\\left[i\\right]\\:\\#\\left(2\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eFinally, a GLMM including application frequency as a continuous variable was used to estimate the dose-response relationship between application frequency and the number of emerging adult insects. The predicted insect reduction rates were derived across application frequencies and taxonomic groups (Eq.\u0026nbsp;3).\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}{log}\\left(E\\left[{Y}_{i}\\right]\\right)=\\:{\\beta\\:}^{0}+\\:{\\beta\\:}^{1}\\upsilon\\:ᵢ\\:+\\:{\\beta\\:}_{2}\\tau\\:ᵢ\\:+\\:{\\beta\\:}_{3}\\rho\\:\\:+\\:\\mu\\:1\\left[i\\right]+\\:\\mu\\:2\\left[i\\right]\\#\\left(3\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eAlthough the inclusion of precipitation and temperature did not consistently improve model fit, as indicated by the AIC, across all taxonomic groups, these variables were retained to ensure comparability between groups.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eVariables and model terms used in the linear models\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"3\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eVariable\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDescription\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eUnits\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eY₁\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eObserved mean mosquito count at trap \u003cem\u003ei\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\stackrel{-}{x}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eE[Y\u003csub\u003ei\u003c/sub\u003e], \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\eta\\:}_{i}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eExpected mosquito\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eMean count (per trap)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eυ\u003csub\u003ei\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency of larvicide application at trap \u003cem\u003ei\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u0026#120793;(υy\u003csub\u003ei\u003c/sub\u003e = j)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eIndicator function for application frequency level \u003cem\u003ej\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\in\\:0.1,\\:0.125,\\:0.167,\\:0.2,\\:0.5\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eτ\u003csub\u003ei\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eMean temperature at trap \u003cem\u003ei\u003c/em\u003e during sampling period\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u0026deg;C\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eρ\u003csub\u003ei\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePrecipitation one week after sampling at trap \u003cem\u003ei\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003emm\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003et\u003csub\u003ei\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTime since larvicide was last applied at trap \u003cem\u003ei\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eDays\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u0026micro;\u003csub\u003e1\u003c/sub\u003e[i]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRandom intercept for trap location\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1-180\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u0026micro;\u003csub\u003e2\u003c/sub\u003e[i]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRandom intercept for sampling day\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eCalendar days\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eb\u003csub\u003e1\u003c/sub\u003e[i]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRandom effect for trap (in GAMM context)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1-180\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eb\u003csub\u003e2\u003c/sub\u003e[i]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRandom effect for day (in GAMM context)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eCalendar days\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ef()\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSmooth function (thin plate spline)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eβ₀\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eIntercept (fixed effect)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eMean count (per trap)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eβⱼ\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCoefficients for model predictors\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eMean count (per trap)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSE_β₁\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eStandard error of frequency coefficient\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ex\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eInput frequency sequence used for predictions\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eseq(0, 0.5, by =\u0026thinsp;0.001)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eR\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePredicted mosquito reduction\u0026thinsp;=\u0026thinsp;\u003cem\u003e100(1\u0026thinsp;\u0026minus;\u0026thinsp;exp(β\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e\u003cem\u003ex))\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e%\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eDuring the sampling period, seven catch basins were excluded due to the absence of water accumulation (4), construction work obstructing access (1), flooding of a residential area due to blockage after heavy rain (1) and incidental larvicidal treatment by a third party (1) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). A total of two, two, one, one, one and zero catch basins were excluded for the control and the 2-, 4-, 6-, 8- and 10-week intervals, respectively. The remaining 173 catch basins were monitored weekly. Owing to illness no sampling was executed from 23 September to 30 September 2024. A total of 2,076 trap observations were recorded with 12.6% of the data containing missing values, primarily due to trap displacement caused by heavy rainfall.\u003c/p\u003e\u003cp\u003eMore than half of the collection cups (58.8%) were empty, whereas the remaining ones contained one or more individuals, resulting in a total of 4,936 collected dipterans. Owing to desiccation or physical damage, 3.4% of specimens could not be reliably identified, leaving 4,768 individuals for taxonomic classification. Most of the specimens caught in the traps were \u003cem\u003eCulex\u003c/em\u003e spp. (53.2%), followed by \u003cem\u003eChironomidae\u003c/em\u003e spp. (31.1%), \u003cem\u003ePsychodidae\u003c/em\u003e (6.4%) and \u003cem\u003eAe. albopictus\u003c/em\u003e. (5.8%). A randomly selected subsample of 81 \u003cem\u003eCulex\u003c/em\u003e spp. was identified as entirely \u003cem\u003eCulex pipiens\u003c/em\u003e, except for one specimen that could only be identified to the \u003cem\u003eCulex\u003c/em\u003e genus level, supporting the assumption that most \u003cem\u003eCulex\u003c/em\u003e specimens were likely \u003cem\u003eCx. pipiens\u003c/em\u003e. All Psychodidae were members of the subfamily Psychodinae.\u003c/p\u003e\u003cp\u003e\u003cb\u003eEffect of application frequency on the abundance of mosquitoes and non-target species\u003c/b\u003e\u003c/p\u003e\u003cp\u003eAnalysis of the untreated control catch basins revealed clear seasonal patterns in dipteran abundance, with \u003cem\u003eCulex\u003c/em\u003e spp. showing the highest activity (7.72 individuals/trap), followed by Chironomidae (1.36), \u003cem\u003eAe. albopictus\u003c/em\u003e (0.41) and Psychodidae (0.34). The peak activity for all taxonomic groups occurred around (ISO) calendar week 35 (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Intriguingly, \u003cem\u003eCulex\u003c/em\u003e spp. exhibited a sharp peak followed by a rapid decline, whereas \u003cem\u003eAe. albopictus\u003c/em\u003e maintained low but stable numbers throughout the season, exceeding one individual only during calendar weeks 35 and 40 (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eLarvicide treatments with VectoMax\u0026reg; FG substantially suppressed adult emergence compared with the untreated catch basins, with reductions most pronounced within 1 to 2 weeks post-application (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). For \u003cem\u003eAe. albopictus\u003c/em\u003e, application frequencies of 2 to 6 weeks maintained low abundance (0.01\u0026ndash;0.05 mosquitoes/trap), whereas frequencies of 8 and 10 weeks were less effective, particularly the 10-week interval, which closely resembled control levels. The model results (Eq.\u0026nbsp;1) indicated statistically significant suppression at application intervals of 6 weeks or shorter, with no significant associations observed for temperature or precipitation (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eCompared with those of the control, \u003cem\u003eCulex\u003c/em\u003e spp. trap counts were consistently lower across all application frequencies (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The GLMM results from Eq.\u0026nbsp;1 confirmed a significant negative association between all treatment intervals and \u003cem\u003eCulex\u003c/em\u003e spp. abundance (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The effect of VectoMax\u0026reg; FG was also more pronounced on \u003cem\u003eCulex\u003c/em\u003e spp. than on \u003cem\u003eAe. albopictus\u003c/em\u003e, indicating greater sensitivity to the larvicide. Additionally, temperature was positively associated with \u003cem\u003eCulex\u003c/em\u003e spp. count, whereas precipitation was negatively associated with Culex spp. count (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). In chironomids and psychodids, the model results (Eq.\u0026nbsp;1) indicate a significant decline in abundance at intervals of 4 weeks or shorter. Temperature had a statistically significant positive effect on chironomid abundance but a statistically significant negative effect on psychodids, whereas precipitation was not significantly associated with either group (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eEffects of VectoMax\u0026reg; FG application frequencies on the abundance of \u003cem\u003eAedes albopictus\u003c/em\u003e, \u003cem\u003eCulex\u003c/em\u003e spp., Chironomidae and Psychodidae in catch basins\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTaxon\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eModel predictor\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eCoefficient\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e95% Confidence interval\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cem\u003eP\u003c/em\u003e-value\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eAedes albopictus\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency (10 weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1.07\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.31\u0026ndash;3.68\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003en.s.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency (8 weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.47\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.13\u0026ndash;1.72\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003en.s.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency (6 weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.04\u0026ndash;0.64\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.010\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency (4 weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.03\u0026ndash;0.49\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.004\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency (2 weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.00\u0026ndash;0.17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTemperature (\u0026deg;C)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1.05\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.98\u0026ndash;1.14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003en.s.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePrecipitation (mm) \u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.93\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.85\u0026ndash;1.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003en.s.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eCulex\u003c/em\u003e spp.\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency (10 weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.01\u0026ndash;0.08\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency (8 weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.06\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.02\u0026ndash;0.18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency (6 weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.00\u0026ndash;0.04\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency (4 weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.00\u0026ndash;0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency (2 weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.00\u0026ndash;0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTemperature (\u0026deg;C)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1.20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1.10\u0026ndash;1.30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePrecipitation (mm) \u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.92\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.85\u0026ndash;0.99\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.024\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eChironimidae\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency (10 weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.59\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e0.21\u0026ndash;1.63\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003en.s.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency (8 weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.39\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e0.14\u0026ndash;1.12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003en.s.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency (6 weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.37\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e0.13\u0026ndash;1.04\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003en.s.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency (4 weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.19\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e0.07\u0026ndash;0.57\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.002\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency (2 weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.06\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e0.02\u0026ndash;0.19\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTemperature (\u0026deg;C)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1.06\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e1.00\u0026ndash;1.12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.039\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePrecipitation (mm) \u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.98\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e0.95\u0026ndash;1.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003en.s.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePsychodidae\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency (10 weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e0.08\u0026ndash;3.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003en.s.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency (8 weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e0.02\u0026ndash;1.20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003en.s.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency (6 weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e0.03\u0026ndash;1.07\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003en.s.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency (4 weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e0.00\u0026ndash;0.19\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFrequency (2 weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.03\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e0.00\u0026ndash;0.25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTemperature (\u0026deg;C)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.85\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e0.76\u0026ndash;0.96\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.01\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePrecipitation (mm) \u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.96\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e0.92\u0026ndash;1.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003en.s.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003csup\u003e1\u003c/sup\u003e Precipitation with a lag of 1 week. 95% CI: 95% confidence interval. Estimates and 95% CIs are based on the GLMM in Eq.\u0026nbsp;1.\u003c/p\u003e\u003cp\u003e\u003cb\u003eResidual effect on adult insect abundance\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe model results (Eq.\u0026nbsp;2) on residual effects revealed significant non-linear effects of time since treatment across all the taxa (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Incorporating a random intercept for trap ID substantially improved model fit by accounting for consistent differences among traps, indicating that traps with higher mosquito counts in one week tended to have higher counts in subsequent weeks. Additionally, calendar time (days) was a good predictor of \u003cem\u003eAe. albopictus\u003c/em\u003e, \u003cem\u003eCulex\u003c/em\u003e spp. and Chironomidae abundance, whereas no significant temporal trend was observed for Psychodidae abundance. Among the environmental covariates, one-week lagged precipitation and a 1\u0026deg;C increase above the mean temperature significantly influenced Chironomidae abundance, with temperature showing a positive association and precipitation showing a negative association (Additional file 1: Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). In contrast, only precipitation had a statistically significant negative effect on \u003cem\u003eAe. albopictus\u003c/em\u003e and \u003cem\u003eCulex\u003c/em\u003e spp. abundance, whereas no significant associations were observed for Psychodidae. Suppression of both target and non-target taxa was most pronounced shortly after treatment, with predicted abundance reductions peaking during the first 19 days for \u003cem\u003eCulex\u003c/em\u003e spp., 20 days for \u003cem\u003eAe. albopictus\u003c/em\u003e, 23 days for Chironomidae and 29 days for Psychodidae. \u003cem\u003eCulex\u003c/em\u003e spp. showed sustained high suppression (\u0026gt;\u0026thinsp;80%) throughout this initial period, whereas \u003cem\u003eAe. albopictus\u003c/em\u003e remained above 80% suppression until day 36 and retained moderate efficacy (\u0026gt;\u0026thinsp;50%) up to day 46. Among the non-target taxa, Chironomidae experienced moderate reductions lasting through day 35, whereas Psychodidae showed sharper and more prolonged suppression, with reductions exceeding 80% up to day 34 and remaining moderate until day 45.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eDose-response effects of application frequency on adult insect abundance\u003c/b\u003e\u003c/p\u003e\u003cp\u003eIn the continuous dose-response model (Eq.\u0026nbsp;3), the \u003cem\u003eAe. albopictus\u003c/em\u003e abundance was significantly influenced solely by application frequency, which was strongly negatively associated with the number of \u003cem\u003eAe. albopictus\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, Additional file 1: Table \u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e). Neither temperature nor lagged precipitation had a statistically significant effect. Model predictions indicate that reductions in \u003cem\u003eAe. albopictus\u003c/em\u003e abundance increased with more frequent applications, with a 73.9% reduction at the 8-week interval, which is currently implemented in several urban areas in Switzerland (pers. comm. Swiss Mosquito Network). According to the model prediction, suppression exceeds 80% at the 5-week interval, surpasses 90% with treatments every 4 weeks, and approaches near-complete control (99%) with biweekly applications. Additionally, variability in predicted abundance declined sharply with increasing treatment frequency, as reflected by narrowing 95% confidence intervals, suggesting a reduced risk of population resurgence. Marginal gains in reduction increased steadily up to the 4-week interval, peaking at 5.7%, before subsequently declining.\u003c/p\u003e\u003cp\u003eIn contrast, \u003cem\u003eCulex\u003c/em\u003e spp. abundance was significantly affected by all three predictors. The application frequency has a strong negative effect; temperature is positively associated \u0026ndash; each 1\u0026deg;C increase above the mean (19.6\u0026deg;C) significantly elevates counts \u0026ndash; and precipitation lag exerts a smaller but significant negative effect (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, Additional file 1: Table S3). The predicted reductions in \u003cem\u003eCulex\u003c/em\u003e spp. exceeds 80% \u0026ndash; even at the 8-week application interval \u0026ndash; and reaches over a 90% reduction with an application frequency every 4 weeks, and near-complete suppression at 2- to 3-week intervals. Like in \u003cem\u003eAe\u003c/em\u003e. \u003cem\u003ealbopictus\u003c/em\u003e, variability in abundance across catch basins declines as application frequency increases, although re-emergence fluctuations are less pronounced. Marginal gains peak at the 7-week interval (3.8%) and decrease rapidly at shorter application frequencies (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, Additional file 1: Table S3).\u003c/p\u003e\u003cp\u003eFor the non-target taxonomic groups, application frequency is also a significant predictor. Temperature has contrasting effects, with a positive relationship observed for Chironomidae abundance and a negative association for Psychodidae abundance. Precipitation lag was not a significant predictor for either group (Additional file 1: Table S3). The predicted reductions in non-target abundance increased with higher treatment frequency, with the abundance of Chironomidae being reduced by 43.6% at 10-week intervals and up to 94.3% under biweekly treatments. The degree of Psychodidae reduction ranged from 55.5% (10-week interval) to 98.3% (2-week interval). Marginal gains differed between taxa: Chironomidae gains increased steadily with shorter intervals, reaching a maximum of 9.2%, whereas Psychodidae gains peaked at a 6-week interval (6.6%) before diminishing at higher frequencies (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, Additional file 1: Table S3).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis study demonstrated that the frequency of VectoMax\u0026reg; FG application is a critical factor for effectively controlling \u003cem\u003eAe. albopictus\u003c/em\u003e and \u003cem\u003eCulex\u003c/em\u003e spp. in urban catch basins. While both taxa were significantly suppressed, \u003cem\u003eCulex\u003c/em\u003e spp. responded consistently well across all the tested frequencies, indicating increased sensitivity to the larvicide. Application intervals longer than 5 weeks led to reduced efficacy and increased variability in mosquito counts, particularly for \u003cem\u003eAe. albopictus\u003c/em\u003e. Across both taxa, more frequent treatments resulted in narrower confidence intervals, indicating greater stability in population control. These findings support the manufacturer\u0026rsquo;s recommended 4-week interval and caution against extending application intervals beyond 5 weeks, especially in areas where \u003cem\u003eAe. albopictus\u003c/em\u003e is a primary concern.\u003c/p\u003e\u003cp\u003eThis study has several limitations to consider. The adult mosquito emergence traps used lacked protective covers, which may have allowed rainwater to flush out mosquitoes, potentially lowering catch numbers and complicating the assessment of precipitation effects. While the measurement error of these traps has not been fully quantified, a comparison of their seasonal trends with those of previous years revealed consistent patterns, supporting their effectiveness for temporal monitoring [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. However, the limited research on species-specific mosquito dynamics in Switzerland highlights the need for more targeted surveillance to refine local vector control strategies. Microclimatic conditions within catch basins \u0026ndash; such as temperature, humidity, and water retention \u0026ndash; were not continuously monitored, limiting our understanding of how basin-specific environmental variability may influence larvicide persistence or mosquito emergence. This is particularly relevant for \u003cem\u003eAe. albopictus\u003c/em\u003e, which remained active until late October, suggesting that thermal buffering within catch basins may have extended its breeding season [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Furthermore, although the biological response to larvicide application frequency is inherently non-linear, we adopted a linear representation to provide a simplified and practical framework for operational guidance. This trade-off balances model complexity with clarity, offering control programmes a more straightforward decision-making tool. Finally, as this study was conducted within a single urban region, caution should be exercised in generalising the findings to areas with different climatic, infrastructural or ecological characteristics.\u003c/p\u003e\u003cp\u003e\u003cem\u003eBacillus thuringiensis\u003c/em\u003e var. \u003cem\u003eisraelensis\u003c/em\u003e and \u003cem\u003eL. sphaericus\u003c/em\u003e are key components of environmentally sustainable vector control programmes, which are valued for their high specificity toward mosquito larvae and minimal toxicity to vertebrates and most non-target organisms. These microbial larvicides act through parasporal crystal protoxins that, upon ingestion, are solubilised and activated in the alkaline midgut of mosquito larvae. The activated toxins bind to specific receptors on midgut epithelial cells, leading to pore formation, cell lysis and larval death. \u003cem\u003eBacillus thuringiensis\u003c/em\u003e var. \u003cem\u003eisraelensis\u003c/em\u003e is known for its rapid action but limited environmental persistence, typically requiring reapplication within two to four weeks [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. In contrast, \u003cem\u003eL. sphaericus\u003c/em\u003e exhibits longer-lasting efficacy, owing to its ability to reproduce within the cadavers of affected insect larvae, thereby sustaining its larvicidal activity through recycling. When used in combination, \u003cem\u003eBti\u003c/em\u003e and \u003cem\u003eL. sphaericus\u003c/em\u003e are intended to provide both immediate and prolonged mosquito control [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Indeed, the dual-action formulation of VectoMax\u0026reg; FG \u0026ndash; which combines \u003cem\u003eBti\u003c/em\u003e for rapid knockdown with \u003cem\u003eL. sphaericus\u003c/em\u003e for residual activity \u0026ndash; appears to provide a synergistic benefit [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Nonetheless, the progressive decline in efficacy beyond 3 to 5 weeks post-treatment suggests that the residual component alone is insufficient for sustained suppression of species such as \u003cem\u003eAe. albopictus\u003c/em\u003e, underscoring the need for timely reapplications.\u003c/p\u003e\u003cp\u003eThe results highlight the importance of tailoring larvicide application intervals to species-specific biology. The higher sensitivity of \u003cem\u003eCulex\u003c/em\u003e spp. may reflect ecological and physiological traits, such as slower feeding rates, habitat preferences and increased susceptibility to \u003cem\u003eL. sphaericus\u003c/em\u003e components of the larvicide [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Previous studies support these patterns; for example, competitive interactions under limited food conditions have shown that \u003cem\u003eAedes aegypti\u003c/em\u003e can outcompete \u003cem\u003eCx. quinquefasciatus\u003c/em\u003e, potentially explaining some of the observed differences in control efficacy [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eComparisons with previous studies confirm the general pattern of residual activity following VectoMax\u0026reg; FG application but also highlight notable variability across different ecological settings. For example, a semi-field trial conducted in Brazil demonstrated the suppression of \u003cem\u003eAe. albopictus\u003c/em\u003e for up to eight weeks and \u003cem\u003eCulex\u003c/em\u003e spp. for nine weeks using a similar larvicide formulation [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Similarly, a field study in Ticino, Switzerland, reported reductions of approximately 60% in \u003cem\u003eAe. albopictus\u003c/em\u003e and up to 85% in \u003cem\u003eCulex\u003c/em\u003e spp. within five to ten weeks post-application [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. These findings are broadly consistent with our results; however, our data suggest a need for more frequent reapplications to sustain high control levels, particularly for \u003cem\u003eAe. albopictus\u003c/em\u003e, potentially reflecting local environmental factors.\u003c/p\u003e\u003cp\u003eOne study documented the efficacy of VectoMax\u0026reg; FG in challenging field conditions, including vegetated environments with high organic content, where residual effects against \u003cem\u003eCulex\u003c/em\u003e spp. persisted for up to 36 days [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Laboratory studies under controlled conditions have reported even longer durations of efficacy, although often at application rates substantially exceeding field recommendations. For example, one study using 57.7 g/m\u0026sup2; VectoMax\u0026reg; FG in catch basin analogues reported complete suppression for up to one year [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e], whereas other laboratory experiments achieved\u0026thinsp;\u0026gt;\u0026thinsp;80% control of \u003cem\u003eAe. aegypti\u003c/em\u003e for over 23 weeks with elevated \u003cem\u003eBti\u003c/em\u003e concentrations [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. These extended durations are unlikely to be replicated under field conditions because of the environmental degradation of active ingredients. As seen in the present study, susceptibility patterns among target species further complicate efficacy outcomes. \u003cem\u003eCulex quinquefasciatus\u003c/em\u003e and \u003cem\u003eAnopheles gambiae\u003c/em\u003e exhibit comparable reduction rates during the first nine days following treatment with \u003cem\u003eBti\u003c/em\u003e or \u003cem\u003eL. sphaericus\u003c/em\u003e [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. In contrast, \u003cem\u003eAe. aegypti\u003c/em\u003e has notably lower susceptibility to \u003cem\u003eL. sphaericus\u003c/em\u003e, with minimal reductions observed at practical dosages, whereas \u003cem\u003eAe. albopictus\u003c/em\u003e appears moderately susceptible [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn addition to efficacy, ecological safety remains a cornerstone of integrated mosquito management strategies. Despite their generally high specificity, larvicide treatments can have unintended ecological effects on non-target dipteran taxa such as chironomids and psychodids. These taxa play critical roles in the decomposition of organic matter and nutrient cycling in aquatic ecosystems, particularly in polluted or eutrophic habitats such as urban catch basins. Disruption of these communities may have cascading effects on higher trophic levels and alter ecosystem functioning [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. The Ticino study reported a 50% reduction in chironomid populations seven weeks after \u003cem\u003eBti\u003c/em\u003e application [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], a pattern found in our findings and in others, such as a semi-field trial in Germany, which reported chironomid reductions ranging from 39\u0026ndash;68% [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. While these reductions indicate some non-target effects, their magnitude remains substantially lower than that observed for mosquito larvae, supporting the selective action of bacterial larvicides. Furthermore, a field study in Cameroon found no significant changes in zooplankton or macroinvertebrate diversity or abundance following VectoMax\u0026reg; FG application, reinforcing its ecological compatibility when used according to guidelines [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. Similarly, other studies have reported minimal effects of \u003cem\u003eBti\u003c/em\u003e on aquatic nutrient dynamics and no measurable impacts on riparian spider populations, suggesting limited disruption to broader ecosystem functions [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eOur findings reinforce the importance of following the label instructions provided by the manufacturer when applying VectoMax FG. Balancing effective mosquito suppression with ecological considerations \u0026ndash; particularly with respect to non-target impacts \u0026ndash; requires careful calibration of treatment schedules to optimise both vector control and environmental stewardship.\u003c/p\u003e\u003cp\u003eFuture studies should aim to better understand the influence of environmental factors \u0026ndash; particularly rainfall \u0026ndash; on mosquito catch data by employing traps equipped with rain shields and by directly measuring water levels within catch basins. In addition, incorporating continuous microclimate monitoring, including temperature and humidity sensors, would offer valuable insights into site-specific conditions that may influence larvicide persistence and mosquito emergence. This is especially relevant for \u003cem\u003eAe. albopictus\u003c/em\u003e, which remained active through late October in our study area, indicating a potential shift in seasonal emergence patterns likely driven by thermal buffering within urban catch basins. A more detailed understanding of these microclimatic dynamics could inform the timing and frequency of larvicide applications and help ensure more reliable seasonal coverage.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eOur findings indicate that the reapplication of VectoMax\u0026reg; FG at 5-week intervals is necessary to achieve effective suppression of both \u003cem\u003eAe. albopictus\u003c/em\u003e and \u003cem\u003eCulex\u003c/em\u003e spp. While \u003cem\u003eCulex\u003c/em\u003e spp. showed robust sensitivity even at extended intervals, \u003cem\u003eAe. albopictus\u003c/em\u003e required more frequent treatments to prevent population rebound. The application frequency influenced not only the suppression level but also the variability in mosquito abundance, contributing to more stable vector control. These results support the integration of optimised treatment intervals into mosquito management programmes while emphasising the need for localised adjustments on the basis of ecological conditions and operational feasibility.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eAe.\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eAedes\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eBti\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eBacillus thuringiensis var. israelensis\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eCx.\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eCulex\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eFG\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eFine granule\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eLDPE\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eLow-density polyethylene foam\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003eAcknowledgement\u003c/p\u003e\n\u003cp\u003eWe would like to thank Eren Kahraman, Elena Sp\u0026ouml;rri, Svenja Zehnder and Giulian Meier for their help during the fieldwork. Many thanks also to Oscar Anido, Frank Bluess and Till Koeppel from the civil engineering office (\u0026lsquo;Tiefbauamt\u0026rsquo;) of the Canton of Basel-Stadt for their expertise and help with equipment, information about the catch basin system and their help whenever problems occurred. Furthermore, we would like to thank Valentina Campana and Eleonora Flacio from the University of Applied Sciences and Arts of Southern Switzerland (SUPSI) for sharing their expertise in designing the emergence traps. Finally, we thank Hans Bossler, Susanne Biebinger and Ann-Christin Honnen from the Cantonal Laboratory Basel-Stadt for facilitating and supporting the project.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFunding\u003c/p\u003e\n\u003cp\u003eThe study received funding from the Cantonal Laboratory Basel-Stadt (KLBS), Switzerland.\u003c/p\u003e\n\u003cp\u003eAvailability of data and materials\u003c/p\u003e\n\u003cp\u003eThe dataset supporting the conclusions of this article is included in Additional file 2.\u003c/p\u003e\n\u003cp\u003eAuthor contributions\u003c/p\u003e\n\u003cp\u003ePM, BM, and TAS conceptualised and designed the study. TK and TAS were responsible for data processing. TK conducted all the analyses; prepared the results, figures and supplementary materials; and drafted the initial manuscript. PM, BM and TAS contributed to critical review and interpretation of the findings. TK and PM finalised and edited the manuscript. All authors reviewed and approved the final version.\u003c/p\u003e\n\u003cp\u003eEthics approval and consent to participate\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003eConsent for publication\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003eCompeting interests\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMedlock JM, Hansford KM, Schaffner F, Versteirt V, Hendrickx G, Zeller H, et al. A review of the invasive mosquitoes in Europe: ecology, public health risks, and control options. Vector Borne Zoonotic Dis. 2012;12(6):435\u0026ndash;47.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOliveira S, Rocha J, Sousa CA, Capinha C. Wide and increasing suitability for \u003cem\u003eAedes albopictus\u003c/em\u003e in Europe is congruent across distribution models. Sci Rep. 2021;11(1).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGossner CM, Ducheyne E, Schaffner F. Increased risk for autochthonous vector-borne infections transmitted by \u003cem\u003eAedes albopictus\u003c/em\u003e in continental Europe. Euro Surveill. 2018;23(24).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBrem J, Elankeswaran B, Erne D, Hedrich N, Lovey T, Marzetta V, et al. Dengue \u0026ldquo;homegrown\u0026rdquo; in Europe (2022 to 2023). New Microbes New Infect. 2023;56.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ede Wispelaere M, Despr\u0026egrave;s P, Choumet V. European \u003cem\u003eAedes albopictus\u003c/em\u003e and \u003cem\u003eCulex pipiens\u003c/em\u003e are competent vectors for Japanese encephalitis virus. PLoS Negl Trop Dis. 2017;11(1).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRichards SL, Anderson SL, Lord CC, Smartt CT, Tabachnick WJ. Relationships between infection, dissemination, and transmission of West Nile virus RNA in \u003cem\u003eCulex pipiens quinquefasciatus\u003c/em\u003e (Diptera: Culicidae). J Med Entomol. 2012;49(1):132\u0026ndash;42.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDiaz LA, Flores FS, Beranek M, Rivarola ME, Almir\u0026oacute;n WR, Contigiani MS. Transmission of endemic St Louis encephalitis virus strains by local \u003cem\u003eCulex quinquefasciatus\u003c/em\u003e populations in Cordoba, Argentina. Trans R Soc Trop Med Hyg 2013;107(5):332\u0026ndash;4.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eScheuch DE, Sch\u0026auml;fer M, Eiden M, Heym EC, Ziegler U, Walther D, et al. Detection of Usutu, Sindbis, and Batai viruses in mosquitoes (Diptera: \u003cem\u003eCulicidae\u003c/em\u003e) collected in Germany, 2011\u0026ndash;2016. Viruses. 2018;10(7).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eVloet RP, Vogels CB, Koenraadt CJ, Pijlman GP, Eiden M, Gonzales JL, et al. Transmission of Rift Valley fever virus from European-breed lambs to \u003cem\u003eCulex pipiens\u003c/em\u003e mosquitoes. PLoS NTDs. 2017;11(12).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFerraguti M, Heesterbeek H, Mart\u0026iacute;nez-de la Puente J, Jim\u0026eacute;nez‐Clavero M\u0026Aacute;, V\u0026aacute;zquez A, Ruiz S, et al. The role of different \u003cem\u003eCulex\u003c/em\u003e mosquito species in the transmission of West Nile virus and avian malaria parasites in Mediterranean areas. Transbound Emerg Dis. 2021;68(2):920\u0026ndash;30.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eNchoutpouen E, Talipouo A, Djiappi-Tchamen B, Djamouko-Djonkam L, Kopya E, Ngadjeu CS, et al. \u003cem\u003eCulex\u003c/em\u003e species diversity, susceptibility to insecticides and role as potential vector of Lymphatic filariasis in the city of Yaound\u0026eacute;, Cameroon. PLoS Negl Trop Dis. 2019;13(4).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRydzanicz K, Jawień P, Lonc E, Modelska M. Assessment of productivity of \u003cem\u003eCulex\u003c/em\u003e spp. larvae (Diptera: \u003cem\u003eCulicidae\u003c/em\u003e) in urban storm water catch basin system in Wrocław (SW Poland). Parasitol Res. 2016;115:1711\u0026ndash;20.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMarcolin L, Zardini A, Longo E, Caputo B, Poletti P, Di Marco M. Mapping the habitat suitability of \u003cem\u003eCulex pipiens\u003c/em\u003e in Europe using ensemble bioclimatic modelling. bioRxiv. 2025.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBrugman VA, Hern\u0026aacute;ndez-Triana LM, Medlock JM, Fooks AR, Carpenter S, Johnson N. The role of \u003cem\u003eCulex pipiens\u003c/em\u003e L.(Diptera: \u003cem\u003eCulicidae\u003c/em\u003e) in virus transmission in Europe. Int J Environ Health Res. 2018;15(2):389.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFlacio E, L\u0026uuml;thy P, Patocchi N, Guidotti F, Tonolla M, Peduzzi R. Primo ritrovamento di \u003cem\u003eAedes albopictus\u003c/em\u003e in Svizzera. Boll Della Soc Ticinese Sci Nat. 2004;92:141\u0026ndash;2.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eM\u0026uuml;ller P, Engeler L, Vavassori L, Suter T, Guidi V, Gschwind M, et al. Surveillance of invasive \u003cem\u003eAedes\u003c/em\u003e mosquitoes along Swiss traffic axes reveals different dispersal modes for \u003cem\u003eAedes albopictus\u003c/em\u003e and \u003cem\u003eAe. japonicus\u003c/em\u003e. PLoS Negl Trop Dis. 2020;14(9).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBellini R, Michaelakis A, Petrić D, Schaffner F, Alten B, Angelini P, et al. Practical management plan for invasive mosquito species in Europe: I. Asian tiger mosquito (\u003cem\u003eAedes albopictus\u003c/em\u003e). Trop Med Infect Dis. 2020;35.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRavasi D, Parrondo Monton D, Tanadini M, Flacio E. Effectiveness of integrated \u003cem\u003eAedes albopictus\u003c/em\u003e management in southern Switzerland. Parasit vectors. 2021;14:1\u0026ndash;15.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFlacio E, Engeler L, Tonolla M, L\u0026uuml;thy P, Patocchi N. Strategies of a thirteen year surveillance programme on Aedes albopictus (Stegomyia albopicta) in southern Switzerland. Parasit Vectors. 2015;8:1\u0026ndash;18.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRavasi D, Monton DP, Tanadini M, Campana V, Flacio E. Efficacy of biological larvicide VectoMax\u0026reg; FG against \u003cem\u003eAedes albopictus\u003c/em\u003e and \u003cem\u003eCulex pipiens\u003c/em\u003e under field conditions in urban catch basins. J Eur Mosq Control Assoc. 2023;42(1):51\u0026ndash;60.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRique HL, Menezes HSG, Melo-Santos MAV, Silva-Filha MHNL. Evaluation of a long-lasting microbial larvicide against \u003cem\u003eCulex quinquefasciatus\u003c/em\u003e and \u003cem\u003eAedes aegypti\u003c/em\u003e under laboratory and a semi-field trial. Parasit Vectors. 2024;17(1):391.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBiebinger S, A-C H. Asiatische Tigerm\u0026uuml;cke - \u0026Uuml;berwachung und Bek\u0026auml;mpfung im Kanton Basel-Stadt 2023. Basel, Kant Lab, Gesundheitsdep Kt Basel-Stadt. 2024:5.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBri\u0026euml;t O; Lindstr\u0026ouml;m A ED, Hul N, Braks M, Petrić D, Schaffner F. 'Reverse' identification key for mosquito species. 2021.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBuck M, Woodley NE, Borkent A, Wood DM, Pape T, Vockeroth JR, et al. Key to Diptera families-adults2009. 95\u0026ndash;156 p.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMarshall A, Kirk-Spriggs H, Muller S, Paiero M, Yau T, Jackson D. Key to Diptera families-adults 122016. 1\u0026ndash;81 p.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eODK Core Team. Get ODK Inc., San Diego, CA, USA; 2024.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eR Core Team. R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna, Austria; 2025.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eCanty A RB. boot: Bootstrap R (S-Plus) Functions. R package version 1.3\u0026ndash;31. ed2024.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBrooks ME, Kristensen K, van Benthem KJ, Magnusson A, Berg CW, Nielsen A, et al. glmmTMB balances speed and flexibility among packages for zero-inflated generalized linear mixed modeling. R J. 2017; 9(2):378\u0026ndash;400.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSN. W. Generalized Additive Models: An Introduction with R. 2 ed. Boca Raton: Chapman and Hall/CRC; 2017.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSchaffner F, Mathis A. Spatio-temporal diversity of the mosquito fauna (Diptera: \u003cem\u003eCulicidae\u003c/em\u003e) in Switzerland. 2013.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFlacio E, Engeler L, Tonolla M, M\u0026uuml;ller P. Spread and establishment of \u003cem\u003eAedes albopictus\u003c/em\u003e in southern Switzerland between 2003 and 2014: an analysis of oviposition data and weather conditions. Parasit Vectors. 2016;9:1\u0026ndash;14.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRavasi D, Mangili F, Huber D, Cannata M, Strigaro D, Flacio E. The effects of microclimatic winter conditions in urban areas on the risk of establishment for \u003cem\u003eAedes albopictus\u003c/em\u003e. Sci Rep. 2022;12(1):15967.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSilva-Filha MHNL, Rom\u0026atilde;o TP, Rezende TMT, Carvalho KdS, Gouveia de Menezes HS, Alexandre do Nascimento N, et al. Bacterial toxins active against mosquitoes: Mode of action and resistance. Toxins. 2021;13(8):523.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eVirgillito C, Manica M, Marini G, Ros\u0026agrave; R, Della Torre A, Martini S, et al. Evaluation of \u003cem\u003eBacillus thuringiensis subsp. israelensis\u003c/em\u003e and \u003cem\u003eBacillus sphaericus\u003c/em\u003e combination against \u003cem\u003eCulex pipiens\u003c/em\u003e in highly vegetated ditches. J Am Mosq Control Assoc. 2022;38(1):40\u0026ndash;5.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBoyce R, Lenhart A, Kroeger A, Velayudhan R, Roberts B, Horstick O. \u003cem\u003eBacillus thuringiensis israelensis\u003c/em\u003e (\u003cem\u003eBti\u003c/em\u003e) for the control of dengue vectors: systematic literature review. Trop Med Int Health. 2013;18(5):564\u0026ndash;77.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLacey LA. \u003cem\u003eBacillus thuringiensis serovariety israelensis\u003c/em\u003e and \u003cem\u003eBacillus sphaericus\u003c/em\u003e for mosquito control. J Am Mosq Control Assoc. 2007;23(sp2):133\u0026ndash;63.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMcMillan JR, Olson MM, Petruff T, Shepard JJ, Armstrong PM. Impacts of \u003cem\u003eLysinibacillus sphaericus\u003c/em\u003e on mosquito larval community composition and larval competition between \u003cem\u003eCulex pipiens\u003c/em\u003e and \u003cem\u003eAedes albopictus\u003c/em\u003e. Sci Rep. 2022;12(1).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSantana-Mart\u0026iacute;nez JC, Molina J, Duss\u0026aacute;n J. Asymmetrical competition between \u003cem\u003eAedes aegypti\u003c/em\u003e and \u003cem\u003eCulex quinquefasciatus\u003c/em\u003e (Diptera: \u003cem\u003eCulicidae\u003c/em\u003e) coexisting in breeding sites. Insects. 2017;8(4):111.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eEritja R. Laboratory tests on the efficacy of VBC60035, a combined larvicidal formulation of \u003cem\u003eBacillus thuringiensis israelensis\u003c/em\u003e (strain AM65-52) and \u003cem\u003eBacillus sphaericus\u003c/em\u003e (strain 2362) against \u003cem\u003eAedes albopictus\u003c/em\u003e in simulated catch basins. J Am Mosq Control Assoc. 2013;29(3):280\u0026ndash;3.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRitchie SA, Rapley LP, Benjamin S. \u003cem\u003eBacillus thuringiensis var. israelensis\u003c/em\u003e (\u003cem\u003eBti\u003c/em\u003e) provides residual control of \u003cem\u003eAedes aegypti\u003c/em\u003e in small containers. Am J Trop Med Hyg. 2010;82(6):1053.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDerua YA, Tungu PK, Malima RC, Mwingira V, Kimambo AG, Batengana BM, et al. Laboratory and semi-field evaluation of the efficacy of \u003cem\u003eBacillus thuringiensis var. israelensis\u003c/em\u003e (Bactivec\u0026reg;) and \u003cem\u003eBacillus sphaericus\u003c/em\u003e (Griselesf\u0026reg;) for control of mosquito vectors in northeastern Tanzania. Curr Res Parasitol Vector-Borne Dis. 2022;2.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSuter T, Crespo MM, de Oliveira MF, de Oliveira TSA, de Melo-Santos MAV, de Oliveira CMF, et al. Insecticide susceptibility of \u003cem\u003eAedes albopictus\u003c/em\u003e and \u003cem\u003eAe. aegypti\u003c/em\u003e from Brazil and the Swiss-Italian border region. Parasit Vectors. 2017;10:1\u0026ndash;11.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAllgeier S, K\u0026auml;stel A, Br\u0026uuml;hl CA. Adverse effects of mosquito control using \u003cem\u003eBacillus thuringiensis var. israelensis\u003c/em\u003e: Reduced chironomid abundances in mesocosm, semi-field and field studies. Ecotoxicol Environ Saf. 2019;169:786\u0026ndash;96.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePoulin B. Indirect effects of bioinsecticides on the nontarget fauna: the Camargue experiment calls for future research. Acta Oecol. 2012;44:28\u0026ndash;32.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eThierry D-N, Djamouko-Djonkam L, Gis\u0026egrave;le FD, Audrey MMP, Timol\u0026eacute;on T, Hubert Z-TS, et al. Assessment of the impact of the biological larvicide VectoMax G: Combination of \u003cem\u003eBacillus thuringiensis\u003c/em\u003e and \u003cem\u003eLysinibacillus sphaericus\u003c/em\u003e on non-target aquatic organisms in Yaound\u0026eacute;-Cameroon. Heliyon. 2023;9(8).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKolbenschlag S, Bollinger E, Gerstle V, Br\u0026uuml;hl CA, Entling MH, Schulz R, et al. Impact across ecosystem boundaries\u0026ndash;Does \u003cem\u003eBti\u003c/em\u003e application change quality and composition of the diet of riparian spiders? Sci Total Environ. 2023;873.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"parasites-and-vectors","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"parv","sideBox":"Learn more about [Parasites \u0026 Vectors](http://parasitesandvectors.biomedcentral.com/)","snPcode":"13071","submissionUrl":"https://submission.nature.com/new-submission/13071/3","title":"Parasites \u0026 Vectors","twitterHandle":"@bugbittentweets","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Mosquito control, Bacillus thuringiensis var. israelensis, Lysinibacillus sphaericus, Aedes albopictus, Culex","lastPublishedDoi":"10.21203/rs.3.rs-7241349/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7241349/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e\u003cp\u003eVectoMax\u0026reg; FG (Valent BioSciences, Libertyville, IL, USA) is a biological mosquito larvicide, combining \u003cem\u003eBacillus thuringiensis\u003c/em\u003e var. \u003cem\u003eisraelensis\u003c/em\u003e and \u003cem\u003eLysinibacillus sphaericus\u003c/em\u003e. \u003cem\u003eBacillus thuringiensis\u003c/em\u003e var. \u003cem\u003eisraelensis\u003c/em\u003e demonstrates a low propensity for resistance development, whereas \u003cem\u003eB. sphaericus\u003c/em\u003e exhibits prolonged residual efficacy in organically polluted aquatic environments. The manufacturer recommends treatments at least every 4 weeks; however, recent evidence suggests that less frequent applications may achieve comparable efficacy, which is important for reducing operational costs related to larvicide volume and labour as well as reduced environmental exposure.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e\u003cp\u003eTo provide data-driven guidance for vector control programmes, we conducted a randomised controlled trial in Basel, Switzerland, from May to October 2024. A total of 180 catch basins, randomly selected from 768 basins in an urban area infested with \u003cem\u003eAedes albopictus\u003c/em\u003e, were assigned to treatment intervals of 2, 4, 6, 8 or 10 weeks, alongside untreated controls. Emergence traps were used to capture adult mosquitoes developing from larvae within the basins, allowing comparison of mosquito abundance reductions across treatment frequencies. Generalised additive and linear mixed effects models were applied to quantify the effects of larvicide application frequency, temperature, precipitation and time since treatment on mosquito and non-target dipteran populations.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003eSuppression of all taxa peaked within 20\u0026ndash;30 days post-treatment. Moderate (\u0026gt;\u0026thinsp;50%) reductions in mosquito abundance were sustained for up to 10 weeks following treatment, with \u003cem\u003eCulex\u003c/em\u003e spp. exhibiting persistent suppression exceeding 80% for up to 8 weeks, and \u003cem\u003eAe. albopictus\u003c/em\u003e maintaining comparably high levels of suppression for up to 5 weeks.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e\u003cp\u003eOur findings show that reapplication of VectoMax\u0026reg; FG at 5-week intervals is necessary for sustained suppression of \u003cem\u003eAe. albopictus\u003c/em\u003e and \u003cem\u003eCulex\u003c/em\u003e spp. While \u003cem\u003eCulex\u003c/em\u003e responded well even at longer intervals, \u003cem\u003eAe. albopictus\u003c/em\u003e required more frequent treatment to avoid rebound. Optimised application frequency not only enhanced control but also reduced variability in mosquito abundance, highlighting the importance of locally tailored treatment schedules in integrated vector management.\u003c/p\u003e","manuscriptTitle":"Optimising the application frequency of VectoMax® FG for the control of Ae. albopictus and Culex spp. in the urban environment: findings from a randomised controlled trial","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-02 10:42:46","doi":"10.21203/rs.3.rs-7241349/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-10-06T16:53:58+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-06T11:31:41+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-24T17:55:23+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"74136661024824039236269879420157752286","date":"2025-09-23T12:50:27+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"150930449564944645615191114559522399681","date":"2025-09-21T14:05:45+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-08-25T12:32:24+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-30T07:53:28+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-07-30T05:39:56+00:00","index":"","fulltext":""},{"type":"submitted","content":"Parasites \u0026 Vectors","date":"2025-07-29T09:00:53+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"parasites-and-vectors","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"parv","sideBox":"Learn more about [Parasites \u0026 Vectors](http://parasitesandvectors.biomedcentral.com/)","snPcode":"13071","submissionUrl":"https://submission.nature.com/new-submission/13071/3","title":"Parasites \u0026 Vectors","twitterHandle":"@bugbittentweets","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"72cc34c4-09f5-41c0-9b15-185c7e0b7dd3","owner":[],"postedDate":"September 2nd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-12-01T16:01:00+00:00","versionOfRecord":{"articleIdentity":"rs-7241349","link":"https://doi.org/10.1186/s13071-025-07169-0","journal":{"identity":"parasites-and-vectors","isVorOnly":false,"title":"Parasites \u0026 Vectors"},"publishedOn":"2025-11-27 15:57:26","publishedOnDateReadable":"November 27th, 2025"},"versionCreatedAt":"2025-09-02 10:42:46","video":"","vorDoi":"10.1186/s13071-025-07169-0","vorDoiUrl":"https://doi.org/10.1186/s13071-025-07169-0","workflowStages":[]},"version":"v1","identity":"rs-7241349","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7241349","identity":"rs-7241349","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}