A molybdenum coordination complex that enables honey bees to mitigate the sublethal toxic effects of fipronil

A molybdenum coordination complex that enables honey bees to mitigate the sublethal toxic effects of fipronil | 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 Short Report A molybdenum coordination complex that enables honey bees to mitigate the sublethal toxic effects of fipronil Loïc Colin-Duchevet, Précillia Cochard, Benjamin Poirot, Jean-Luc Brunet, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8766031/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract This study deals with the effect of the molybdenum-based complex Na 2 [Mo 2 O 4 (EDTA)] used as dietary supplement for the protection of honey bees A. mellifera against deleterious effects of pesticides. Fipronil is a pesticide that is particularly toxic to bees,. In this study, we demonstrate that feeding bees in cages with a 20 mg/L complex solution in sucrose syrup does not significantly alter the value of this lethal dose. However, significant effects are observed at sublethal doses. When bees receive doses of 0.5 ng/bee of fipronil by contact, PER experiments show that their cognitive abilities are significantly reduced. In this study, we demonstrate that bees that have been pre-fed with Na 2 [Mo 2 O 4 (EDTA)] are not affected by this decline in cognitive ability and that a protective effect is clearly evident. This effect is not specific to Fipronil. In fact, in the second part of this study, we show that bees that ingested a cocktail of four pesticides had a higher mortality rate than the control group, but that bees exposed to both this cocktail and the Mo-complex had a mortality rate comparable to that of the control group, thus demonstrating a more comprehensive protective effect. The regulation of molybdenum enzymes such as xanthine oxidase is one hypothesis to explain this effect. In the final part, preliminary results are presented to assess the impact of feeding with our complex on xanthine oxidase levels. Molybdenum coordination complex honey bee pesticide fipronil olfactory learning Figures Figure 1 Figure 2 Figure 3 Full Text Bees provide a vital ecosystem service thanks to their contribution to the maintenance of biodiversity and food production (van der Sluijs et al. 2013). Among the wide variety of bee species, the managed honey bees Apis mellifera play a key role in insect-mediated pollination, while about 80% of all cultivated plant species and 40% of our diet directly depend on pollination (Klein et al., 2007; Aizen et al., 2009). However, Apis mellifera is gravely endangered by colony losses (Potts at al. 2010; Bruckner et al., 2023; Gray et al., 2023; Benito-Murcia et al. 2025), which have dramatically increased in the last decades through a multifactorial process involving biological agents, a lack of resources (Naug, 2009; Tsuruda et al., 2021) and the use of pesticides (Goulson 2015). In this context, the development of new solutions to strengthen bees’ health is of great interest. Pesticides are one of the major drivers behind the recent decline in pollinator populations (Bonmatin et al. 2015; Pisa et al. 2015; Simon-Delso et al. 2015; Giorio et al. 2021; Pisa et al. 2021). Pesticide usage associated with intensive agriculture can have detrimental impacts on honey bees ranging from immediate mortality to sub-lethal effects. The latter are more difficult to demonstrate but they can induce cognitive anomalies in honey bees notably through effects on learning performances, olfaction, visual ability, flight and homing disruptions, and detrimental physiological alterations (Palmer et al. 2013; Fischer et al. 2014; Goñalons and Farina 2018; Chakrabarti et al. 2019; Pudasaini 2020; Kumar et al. 2022). Even if these effects do not directly cause the death of the honey bees and the immediate demise of their colonies, they may become have strong detrimental effects in time. For instance, foragers with memory, orientation and/or physiological impairments might fail to return to their hive, dying from hunger or cold (van der Sluijs et al., 2013). Fipronil is a systemic insecticide that belongs to the phenylpyrazole family and is one of the best-selling insecticide molecules in the world (Bonmatin et al. 2015). Due to its low median lethal dose (LD 50 ) of around 6 ng/bee for acute topical application, fipronil is considered to be highly toxic to bees (European Food Safety Authority, 2013a). The scientific literature is rich in studies demonstrating the sublethal effects of this systemic insecticide on Apis mellifera (Pisa et al. 2015) either by topical application, ingestion, or injection (Decourtye et al. 2005; El Hassani et al. 2005, 2009; Aliouane et al. 2008; Bernadou et al. 2009;). It acts on GABA receptors, which are highly present in the bee brain and are known to play a key role in learning and memory processes, and causes abnormal nervous system activity, convulsions, and death (Tingle et al. 2003; El Hassani et al. 2005, 2009; Holder et al. 2018). Given its toxicity to honeybees, fipronil has been banned in agriculture in France since 2004, but its use is still permitted for treatment against fleas and ticks on pets and against termites due to its lower toxicity to vertebrates. Furthermore, since it is not efficiently removed by conventional water treatment facilities and has a relatively long half-life time in soils ranging from 100 to 200 days depending on climatic conditions (Bonmatin 2015), it is relatively persistent in the environment, particularly in water and pollen consumed by bees. Therefore, even at low concentration these insecticides pose serious risks of undesirable environmental impacts (Simon-Delso et al. 2015) and honey bees can be exposed to potential sublethal doses of fipronil even in countries where this molecule has been banned from agriculture. Quality nutrition is one way to improve honey bee health, reduce mortality (Alaux et al., 2010; Dolezal et al., 2019) and mitigate the effects of other stressors such as pesticides (Castle et al., 2022). However, optimizing bee nutrition requires achieving the right balance between macronutrients and micronutrients, a process that is not always straightforward (Bonoan et al., 2018; Lau et al., 2023). To overcome nutritional limitations, beekeepers rely on feed supplements usually in the form of sugar syrup and fondants, sometimes supplemented with proteins and micronutrients including vitamins and minerals (Lau et al., 2023). Among minerals, trace elements (TE) undoubtedly play a key role, as they are involved in a wide variety of biochemical processes. Honey bees’ needs in TE are met by pollen and water (Bonoan et al., 2018), two sources of TE which however strongly vary among flower species (Bay et al., 2021), environment and climatic conditions across space and time. Surprisingly, however, studies on the importance and needs of TE for honey bee health remain scarce (Herbert, 1979; Zhang et al., 2015). Molybdenum (Mo) is a trace element that plays an essential role in all living organisms (Hill 2002; Mendel 2012), including insects (Dow, 2017). It is involved in a wide variety of enzymes which play a crucial role in the catalysis of redox reactions (Hille, 2002; Schwarz et al., 2009). In eukaryotes, these enzymes mainly belong to the sulfite oxidase (SO) and xanthine oxidase (XO) families (Peng et al., 2018), which are useful for the degradation of xenobiotics with a broad substrate spectrum. In insects, this enzyme mainly exists in the form of xanthine dehydrogenase (XDH), which can be converted into XO under oxidative stress which can be induced by pesticides through the formation of reactive oxygen species (ROS) (Qiao et al. 2005; Chakrabarti et al. 2015). Honey bees naturally contain the Mo trace element at an average level of about 0.4 ppm (Fuior et al. 2025), but its role for honey bee health remains unknown to date. Very recently however, Fuior et al. (2025) and Benito-Murcia et al. (2025) evidenced that Na 2 [Mo 2 O 4 (EDTA)] (Figure 1), a coordination complex of Mo(+V) belonging to a wide family of [Mo 2 O 2 E 2 ] 2+ -based complexes (E = S or O) displaying various biological properties (Fuior et al. 2022; Gretarsdottir et al. 2022), can be efficient as feed supplement to improve the honey bee health. Indeed, feeding beehives with only a few milligrams of this complex, hereafter referred to as Na-Mo 2 O 4 -EDTA , diluted in a sugar syrup (at 0.2 to 2 mg/L) showed prolonged positive effects on the colonies. Na-Mo 2 O 4 -EDTA is assimilated by honey bees in both field and laboratory conditions and does not exhibit any toxicity on honey bees even in case of overdosage. It provokes an increase of the anti-oxidative properties of hemolymph, can induce an increase in honey production up to 49% and a decrease in winter mortality by 44%. Moreover, Fuior et al. (2025) evidenced that feeding bees in laboratory conditions with the complex produces an increase in Mo content in the head and especially in the brain and in the neurolemma, a protective membrane around the brain, which already naturally contain Mo at a low level. The question therefore naturally arises as to whether this load in molybdenum in and around the brain could protect honeybees from the deleterious effects of a systemic insecticide such as fipronil, which is known to have a significant adverse impact on bees’ cognitive performances. The main objective of this study was thus to determine whether the Na-Mo 2 O 4 -EDTA complex could have beneficial effects on bees exposed to a topical fipronil treatment, either on its survival face with a lethal dose of fipronil or on its learning performances when treated with sublethal doses of fipronil. The first part of this communication aims to address this issue while a second part aims investigate if the results obtained with fipronil are specific to this pesticide or could be extended to other chemicals the honey bees could meet in nectar. A first evaluation of the level of xanthine oxidase enzyme, an enzyme potentially representative of molybdenum-dependent oxidase enzymes modulation and related to the level of pesticides (Chakrabarti et al. 2015) is also investigated. In order to assess whether molybdenum treatment could reduce the sensitivity of bees to fipronil exposure, two groups of 300 bees isolated upon emergence were divided into groups of 30 in Pain-type Plexiglas cages (see Figure S2, SI) and placed in an oven at 35°C and 50% humidity. In the control group, bees were fed during 8 days with sucrose solution (50% w/w), water and pollen ad libitum . After 8 days, only water and sugar solution were provided, still ad libitum . In the fipronil groups, sucrose solution was supplemented with Na-Mo 2 O 4 -EDTA at 20 mg/L for the whole duration of feeding. The bees were used in the experiment 14 days after emergence, because worker bees typically become foragers and express strong learning abilities at this age. The bees were first narcotized inside a CO 2 chamber at 10°C (Fig S3A, SI), placed on an ice bed (Fig S3B, SI) and 1 µL of solution of fipronil at 0, 3, 6, 12 or 24 ng/µL in acetone 0.1% in water was applied onto the dorsal part of the thorax. After exposure, the bees were returned to their cage and maintained at 35°C and 50% relative humidity. Two replicates of 30 bees were prepared for each treatment and mortality was recorded at 4, 24 and 48 hours after exposure. The resulting dose-response curves show bees’ mortality rate as a function of the dose of fipronil received (see Fig S4, SI). The curves are very similar for the two groups, which indicates that molybdenum feeding had no impact on honeybee mortality with increasing doses of fipronil. The LD 50 were 5.97 ng/bee and 5.49 ng/bee for molybdenum-treated and control bees respectively, values that are close to that measured (5.93 ng/bee) by European Food Safety Authority (2013b). The difference between the 2 treatments was not significant (t-test, p = 0.49). Likewise, no difference appeared in the slope of the curve (t-test, p = 0.68). Therefore, no significant effects of Na-Mo 2 O 4 -EDTA treatment was found on bees’ resistance to lethal fipronil treatment. Next, we asked if molybdenum treatment could protect bees from the deleterious effects of a sublethal dose of fipronil on bees’ learning performances. The dose of 0.5 ng fipronil per bee was chosen. To do so, bees were subjected to an associative learning task using the conditioning of the proboscis extension reflex (PER), which is known to be a relevant tool to estimate the side effects of stressors on honey bees, in particular pesticides (Pham-Delègue et al. 2002; Giurfa and Sandoz, 2012; Siviter et al., 2018). In this protocol, restrained bees learn to associate an odorant (conditioned stimulus, CS) with a sucrose reward (unconditioned stimulus, US), an association that bees typically form in nature while foraging for nectar (Menzel, 1999; Sandoz, 2011). Two groups of 32-34 bees isolated at emergence were prepared as described above: one control group and one test group fed with Na-Mo 2 O 4 -EDTA at 20 mg/L in sucrose syrup (50% w/w). After 14 days, the bees were narcotized with CO 2 , and each group was split into two experimental groups: one receiving 1 µL of acetone 0.1% in water; one receiving 0.5 ng/bee of fipronil in 1 µL acetone 0.1% in water, in all cases 4 h before performing olfactory conditioning experiments. Four experimental groups were thus constituted as follows: One group of 34 bees fed with sucrose only on which 1 µL of acetone 0.1% in water was applied onto the thorax (“control” group); One group of 32 bees fed with sucrose supplemented with Na-Mo 2 O 4 -EDTA at 20 mg/L on which 1 µL of acetone 0.1% was applied onto the thorax (“Mo only” group) One group of 32 bees fed with sucrose only on which 0.5 ng of fipronil in 1 µL of acetone 0.1% was applied onto the thorax (“fipronil” group) One group of 34 bees fed with sucrose supplemented with Na-Mo 2 O 4 -EDTA at 20 mg/L on which 0.5 ng of fipronil in 1 µL of acetone 0.1% was applied onto the thorax (“fipronil + Mo” group). Figure 2 shows the experimental setup used for the PER tests (Figures 2A and 2B) and the procedure followed for the PER experiment (Figure 2C). The results of the olfactory conditioning procedure performed through 5 successive trials, in which bees associate an olfactory stimulus (CS = 1-hexanol or 1-nonanol) with a sucrose reward (US) are represented in Figure 2D. The olfactory stimulus used as CS (1-hexanol or 1-nonanol) did not influence bees’ learning performances (GLMM, stimulus effect, χ 2 = 0.0072, 1 df, p = 0.93) so that data with both odorants were pooled (raw data are given in the SI). Figure 2D shows that bees learned the CS-US association (GLMM, trials effect, χ 2 = 11.5, 4 df, p = 0.02). In addition, treatments had a significant effect on learning performances (GLMM, trials effect, χ 2 = 11.3, 3 df, p = 0.01). In the control group, bees showed typical learning performances and 81.5% responded to the CS at the 5 th trial. Fipronil presented alone strongly and significantly reduced bees’ ability to associate the odour with the sucrose reward compared with control bees. Only 52% of bees responded to the CS at the end of training for a dose of fipronil less than 10 times lower that the lethal dose, a proportion significantly lower than for the control group while (Tukey contrasts, corrected p = 0.041). On the contrary, in bees that received Na-Mo 2 O 4 -EDTA treatment (group “fipronil+Mo”), fipronil had no such effect and all bees showed good learning performances, reaching the same performance level as control bees (Tukey contrasts, corrected p = 1). Finally, Na-Mo 2 O 4 -EDTA treatment alone had no effect on bees’ learning performance, as shown by the lack of difference between the two groups that received no fipronil (Tukey contrasts, corrected p = 1). Furthermore, the protective effect of Mo can be seen in the significant difference between the “Fipronil” and “Mo+Fipronil” groups (Tukey contrasts, corrected p = 0.041). We conclude that feeding bees with the complex Na-Mo 2 O 4 -EDTA was able to mitigate the negative impact of a sublethal dose of fipronil on bees’ associative learning performances. One hour after conditioning, two retention tests were performed, one with the learned odorant (CS, 1-hexanol or 1-nonanol) and the second with a novel odorant (NoD). This last test shown in Figure 2E, allowed to determine if the association learned during the acquisition phase was specific for the CS. In retention tests performed 1h after training, the same general pattern of results was observed. Treatment significantly influenced responses to the CS (Fisher’s exact test, p = 0.04). Pairwise comparisons revealed that the “fipronil” group that did not receive any Na-Mo 2 O 4 -EDTA treatment, fipronil application significantly reduced bees’ responses to the CS compared to the control group (Fisher’s exact test, corrected p = 0.036). On the contrary, in groups that received Na-Mo 2 O 4 -EDTA treatment, the same level of responses was observed with or without fipronil application (Fisher’s exact test, p > 0.8). The proportion of bees responding to the NoD was smaller or equal to 3% in all groups. Bees responded significantly more to the CS than to the NoD in all groups (Mc Nemar test, p < 0.042). These results show that memory was specific to the CS, even in groups in which performances were impaired by fipronil application. This experiment unambiguously demonstrates that dietary treatment with the complex Na-Mo 2 O 4 -EDTA in a sucrose syrup does not impair honey bees’ olfactory learning abilities, but rather protects them from the deleterious effect of fipronil applied at a sublethal dose. We thus conclude that Na-Mo 2 O 4 -EDTA could help protect beehives from the threats posed by pesticide exposure, here fipronil. Fipronil is one pesticide among many others, and one may wonder whether this protection is specific to fipronil or can extends to other chemicals to which bees are exposed in nature. To address this question two groups of honey bees were intoxicated by ingestion of a cocktail of chemicals containing two fungicides, one insecticide and one chemical used to enhance the insecticidal properties, i.e. imoxystrobine, spiroxamine, phosmet and piperonylbutoxide respectively. These chemicals are known to be toxic for honey bees and are frequently detected in nectar of different flowers (Hayat et al. 2018, Azpiazu et al. 2019). A mixture of these molecules was diluted in Apistar© sugar syrup, following field realistic concentrations found in the literature: 10 µg/L imoxystrobine, 10 µg/L spiroxamine, 10 µg/L phosmet and 10 µg/L piperonylbutoxide. The two groups were constituted of 64 honey bees spread in 4 boxes containing 16 bees each. The first group called “pesticides” was fed ad libitum with sugar syrup containing the cocktail of chemicals, while the second group “pesticides+Mo” was fed ad libitum with sugar syrup containing the cocktail of chemicals and the Na-Mo 2 O 4 -EDTA complex at 2 mg/L, a concentration recently used in field test campaigns (Benito-Murcia et al. 2025). For comparison, a “control” group was constituted with 60 honey bees distributed in 3 boxes and fed with sugar syrup. For each group, bee mortality was registered every 2-3 days during 28 days. Survival curves using the Kaplan-Meier method were constructed for each treatment (Figure 3). Pairwise comparisons by Log-Rank tests show significant differences between “pesticides” and “Control” groups (p value ˂ 0.0001) and between “pesticides” and “pesticides + Mo” groups ((p value ˂ 0.0001). There was however no significant difference between “Control” and “pesticides+Mo” groups (p value = 0.83529), despite the presence of the mixtures of toxic chemicals. This result suggests that the ingestion of the Na-Mo 2 O 4 -EDTA at 2 mg/L together with the pesticide cocktail in the sugar syrup balanced the negative impact of the latter and suggests that feeding honey bees with Na-Mo 2 O 4 -EDTA in syrup could protect bees from various pesticides. The mode of action of Na-Mo 2 O 4 -EDTA is currently unknown. Regulation of detoxifying molybdenum enzymes such as XO is appealing. As preliminary results, the level of XO was determined at different times in abdomen, where the expression of XO is higher, for the three previous groups of honey bees and an additional group constituted by some bees only fed with Na-Mo 2 O 4 -EDTA in syrup (see SI for more details). The number of bees was too limited to get statistically robust conclusions (8 or 9 per group). Nevertheless, at D15 (Figure S7, SI), the level of XO is decreased from control groups to “pesticides” group (p = 0.052), while the level XO for the group fed with Na-Mo 2 O 4 -EDTA only (“Mo-only”) seems intermediate, suggesting that the antioxidative properties of Na-Mo 2 O 4 -EDTA (Fuior et al 2025) could reduce the oxidative stress and thus this level (Chakrabarti et al 2015). Interestingly the level of XO for the group “pesticides + Mo” is found equivalent to that of the group “Mo-only”. This first result is in line with previous results showing the Na-Mo 2 O 4 -EDTA mitigate the impact of pesticides in honey bees and suggest that this complex could regulate the level of the XO enzyme. Further investigations are needed on XO and other molybdo-enzymes at different times, different dosages of Mo-complex, and different parts of the bees, notably in the head to conclude on this hypothesis. In conclusion, this study demonstrates that feeding honeybees with sugar syrup enriched with Na-Mo 2 O 4 -EDTA coordination complex could help protect honey bee colonies from threats related to pesticide exposure. In particular, we have shown that Na-Mo 2 O 4 -EDTA can compensate for the negative sublethal effects of fipronil on honey bees’ cognitive abilities or on mortality induced by the ingestion of a cocktail of chemicals that they may encounter in nature. The mode of action of the complex remains unknown, but its antioxidant properties and its role in regulating xanthine oxidase (as well as xanthine dehydrogenase XDH) may be suggested. These results pave the way for further studies aimed at understanding the mode of action of Na-Mo 2 O 4 -EDTA and developing new complexes of molybdenum and other transition metals to protect honeybees from chemicals present in the environment. Declarations Competing Interests One author (SF) is linked to a patent about the use of this family of complexes for the beekeeping industry (European Patent EP4185594B1 delivered on 4 th december 2024). The authors declare these interests in the interest of full transparency and affirm that the reported findings are presented objectively and without bias. Acknowledgments University of Versailles, INRAE and the CNRS are gratefully acknowledged for financial support. This work was funded by “lune de miel” foundation, the CNRS MITI (call Metallomix, project “MOLYBEE”), and the SATT Paris-Saclay (project APIMONA). Supplementary Information (SI) / data availability The supporting information (SI) contains all details concerning materials and methods. The raw data have been deposited on Mendeley data and are accessible through the link https://data.mendeley.com/preview/vg8bcz44j4?a=92fd174c-0730-48dc-9703-0ece02a96b17 Author contribution statement Fipronil experiments: L.C.; mortality test with a cocktail of pesticides: P.C., B.P.; Xanthine Oxidase mesurements: J.-L.B; Methodology: J.-C.S, B.P. J.-L. B., S.F.; Formal Analysis, L.C., P.C., J.-L.B; Writing-Review and Editing, J.-C. S. and S.F. All authors have read and agreed to the published version of the manuscript. References Aizen MA, Garibaldi LA, Cunningham SA, Klein AM (2009) How much does agriculture depend on pollinators? Lessons from long-term trends in crop production. Ann. Bot. 103: 1579–1588. https://doi.org/10.1093/aob/mcp076 Alaux C, Ducloz F, Crauser D, Le Conte Y (2010) Diet effects on honeybee immunocompetence. Biol. Lett. 6: 562–565. https://doi.org/10.1098/rsbl.2009.0986 Aliouane Y, El Hassani AK, Gary V, Armengaud C, Lambin M, Gauthier M (2009) Subchronic exposure of honeybees to sublethal doses of pesticides: effects on behavior. Environmental Toxicology and Chemistry 28(1): 113. DOI 10.1897/08-110.1 . Azpiazu, C, Bosch J, Viñuela E, Medrzycki P, Teper D, Sgolastra F (2019) Chronic oral exposure to field-realistic pesticide combinations via pollen and nectar: effects on feeding and thermal performance in a solitary bee. Sci Rep. 9: 13770 Bay V, Topal E, Çakıcı N, Yıldızdal İ, Tosunoglu A (2021) Palynological analyses, chemical and mineral composition of some honeybee pollen pellets. Uludağ Arıcılık Derg. 21, 187–197. https://doi.org/10.31467/uluaricilik.996036 Benito-Murcia M, Riva C, García-Vicente EJ, Pérez A, Domínguez MM, Hermosilla N, Cochard P, Hatjina F, Holmiere M, Martínez-Morcillo S, Risco D, Floquet S. (2025) Reducing honey bee winter mortality with molybdenum supplementation: field evidence across Europe. Research in Veterinary Science, 197: 105932. https://doi.org/10.1101/2025.07.23.666091 Bernadou A, Démares F, Couret-Fauvel T, Sandoz JC, Gauthier M (2009) Effect of fipronil on side-specific antennal tactile learning in the honeybee. Journal of Insect Physiology 55(12): 1099–1106. DOI 10.1016/j.jinsphys.2009.08.019 . Bonmatin JM, Giorio C, Girolami V, Goulson D, Kreutzweiser DP, Krupke C, Liess M, Long E, Marzaro M, Mitchell EAD, Noome DA, Simon-Delso N, Tapparo A (2015) Environmental fate and exposure; neonicotinoids and fipronil. Environ Sci Pollut Res 22:35–67, DOI 10.1007/s11356-014-3332-7 Bonoan RE, O’Connor LD, Starks PT (2018) Seasonality of honey bee (Apis mellifera) micronutrient supplementation and environmental limitation. J. Insect Physiol. 107:23–28. Bruckner S, Wilson M, Aurell D, Rennich K, vanEngelsdorp D, Steinhauer N, Williams GR (2023). A national survey of managed honey bee colony losses in the USA: results from the Bee Informed Partnership for 2017–18, 2018–19, and 2019–20. J. Apic. Res. 62: 429–443. https://doi.org/10.1080/00218839.2022.2158586 Castle D, Alkassab AT, Bischoff G, Steffan-Dewenter I, Pistorius J (2022) High nutritional status promotes vitality of honey bees and mitigates negative effects of pesticides. Sci. Total Environ. 806, 151280. https://doi.org/10.1016/j.scitotenv.2021.151280 Chakrabarti P, Rana S, Sarkar S, Smith B, Basu P (2015) Pesticide-induced oxidative stress in laboratory and field populations of native honey bees along intensive agricultural landscapes in two Eastern Indian states., Apidologie, 46: 107–129 Chakrabarti, P., Sarkar, S., Basu, P. (2019) Pesticide induced visual abnormalities in Asian honey bees (Apis cerana L.) in intensive agricultural landscapes. Chemosphere. 230: 51–58 Decourtye A, Devillier J, Genecque E, Le Menach K, Budzinski H, Cluzeau S, Pham-Delègue MH (2005) Comparative Sublethal Toxicity of Nine Pesticides on Olfactory Learning Performances of the Honeybee Apis mellifera. Archives of Environmental Contamination and Toxicology 48(2): 242–250. DOI 10.1007/s00244-003-0262-7 . Dolezal AG, Carrillo-Tripp J, Judd TM, Allen Miller W, Bonning BC, Toth AL (2019) Interacting stressors matter: diet quality and virus infection in honeybee health. R. Soc. Open Sci. 6, 181803. https://doi.org/10.1098/rsos.181803 Dow JA (2017) The essential roles of metal ions in insect homeostasis and physiology. Curr. Opin. Insect Sci. 23: 43–50. El Hassani AK, Dacher M, Gauthier M, Armengaud C (2005) Effects of sublethal doses of fipronil on the behavior of the honeybee (Apis mellifera). Pharmacology Biochemistry and Behavior 82(1): 30–39. DOI 10.1016/j.pbb.2005.07.008 . El Hassani AK, Dupuis JP, Gauthier M, Armengaud C (2009) Glutamatergic and GABAergic effects of fipronil on olfactory learning and memory in the honeybee. Invertebrate Neuroscience 9(2): 91–100. DOI 10.1007/s10158-009-0092-z . European Food Safety Authority. (2013a) Guidance on the risk assessment of plant protection products on bees (Apis mellifera, Bombus spp. and solitary bees). EFSA Journal 11(7). DOI 10.2903/j.efsa.2013.3295 . European Food Safety Authority. (2013b) Conclusion on the peer review of the pesticide risk assessment for bees for the active substance fipronil. EFSA Journal 11, 3158. https://doi.org/10.2903/j.efsa.2013.3158 Fischer J, Mueller T, Spatz AK, Greggers U, Gruenewald B, Menzel R (2014) Neonicotinoids interfere with specific components of navigation in honeybees. PloS. One. 9(3), e91364 Fuior A, Hijazi A, Garbuz O, Bulimaga V, Zosim L, Cebotari D, Haouas M, Toderaş I, Gulea A, Floquet S (2022). Screening of biological properties of Mo V 2 O 2 S 2 - and Mo V 2 O 4 -based coordination complexes: Investigation of antibacterial, antifungal, antioxidative and antitumoral activities versus growing of Spirulina platensis biomass. J. Inorg. Biochem. 226, 111627. https://doi.org/10.1016/j.jinorgbio.2021.111627 Fuior A, Colin-Duchevet L, Cebotari V, Noël A, Ribaud I, Gérard I, Garbuz O, Fregnaux M, López X, Larcher V, Shestopalov MA, Solovieva AO, Pozmogova TN, Gliga O, Railean N, Cochard P, Poirot B, Charistos L, Hatjina F, Somogyi A, Medjoubi K, Gaumer S, Gulea A, Toderas I, Sandoz JC, Floquet S (2025) Feed supplementation with molybdenum complexes improves honey bee health. Inorg. Chem. Front. 12: 7107–7122. Giorio C, Safer A, Sánchez-Bayo F, Tapparo A, Lentola A, Girolami V, Bijleveld van Lexmond M, Bonmatin JM (2021) An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 1: new molecules, metabolism, fate, and transport. Environ Sci Pollut Res 28:11716–11748 https://doi.org/10.1007/s11356-017-0394-3 Giurfa M, Sandoz JC (2012) Invertebrate learning and memory: Fifty years of olfactory conditioning of the proboscis extension response in honeybees. Learning & Memory 19(2):54–66. DOI 10.1101/lm.024711.111 . Goñalons CM, Farina WM (2018) Impaired associative learning after chronic exposure to pesticides in young adult honey bees. J. Exp. Biol. 221(7) Goulson D, Nicholls E, Botias C, Rotheray EL (2015) Bee declines driven by combined stress from parasites, pesticides, and lack of flowers. Science, 347, 1255957. Gray A, Adjlane N, Arab A, Ballis A, Brusbardis V, Bugeja Douglas A, Cadahía L, Charrière JD, Chlebo, R, Coffey MF, Cornelissen B, Costa CAD, Danneels E, Danihlík J, Dobrescu C, Evans G, Fedoriak M, Forsythe I, Gregorc A, Ilieva Arakelyan I, Johannesen J, Kauko L, Kristiansen P, Martikkala M, Martín-Hernández R, Mazur E, Medina-Flores CA, Mutinelli F, Omar EM, Patalano S, Raudmets A, San Martin G, Soroker V, Stahlmann-Brown P, Stevanovic J, Uzunov A, Vejsnaes F, Williams A, Brodschneider R (2023) Honey bee colony loss rates in 37 countries using the COLOSS survey for winter 2019–2020: the combined effects of operation size, migration and queen replacement. J. Apic. Res. 62: 204–210. https://doi.org/10.1080/00218839.2022.2113329 Gretarsdottir JM, Lambert IH, Sturup S, Suman SG (2022) In Vitro Characterization of a Threonine-Ligated Molybdenyl-Sulfide Cluster as a Putative Cyanide Poisoning Antidote; Intracellular Distribution, Effects on Organic Osmolyte Homeostasis, and Induction of Cell Death. ACS Pharmac. Trans. Sci. 5(10): 907–918. Hayat K, Afzal M, Aqueel MA, Khan QM (2018) Determination of Insecticide Residues in Fruits, Vegetables, Pollen, Nectar and Ground Water of Punjab (Pakistan). J. Agric. Res. 56:95–105. Herbert EW (1979) A New Ash Mixture for Honeybees Maintained on a Synthetic Diet. J. Apic. Res. 18, 144–147. https://doi.org/10.1080/00218839.1979.11099958 Hille R (2002) Molybdenum and Tungsten in Biology. Trends Biochem. Sci. 27 (7): 360–367. Holder PJ, Jones A, Tyler CR, Cresswell JE (2018) Fipronil pesticide as a suspect in historical mass mortalities of honey bees. Proceedings of the National Academy of Sciences 115 (51): 13033–13038. DOI 10.1073/pnas.1804934115 . Hosler, J.S., Buxton, K.L., Smith, B.H., 2000. Impairment of olfactory discrimination by blockade of GABA and nitric oxide activity in the honey bee antennal lobes. Behavioral Neuroscience 114, 514–525. https://doi.org/10.1037/0735-7044.114.3.514 Klein AM, Vaissiere BE, Cane JH, Steffan-Dewenter I, Cunningham SA, Krement C, Tscharntke T (2007) Importance of pollinators in changing landscapes for world crops. Proc. Biol. Sci. 274: 303–313. Kumar D, Banerjee D, Chakrabarti P, Sarkar S, Basu P (2022) Oxidative stress and apoptosis in Asian honey bees ( A. cerana) exposed to multiple pesticides in intensive agricultural landscape. Apidologie 53: 25 Lau PW, Esquivel IL, Parys KA, Hung KLJ, Chakrabarti P (2023). The nutritional landscape in agroecosystems: a review on how resources and management practices can shape pollinator health in agricultural environments. Ann. Entomol. Soc. Am. 116: 261–275. Mendel RR, Kruse T (2012) Cell biology of molybdenum in plants and humans. Biochimica et Biophysica Acta 1823: 1568–1579. Menzel, R., 1999. Memory dynamics in the honeybee. Journal of Comparative Physiology A 185, 323–340. https://doi.org/10.1007/s003590050392 Naug D (2009) Nutritional stress due to habitat loss may explain recent honeybee colony collapses. Biol. Conserv. 142: 2369–2372. https://doi.org/10.1016/j.biocon.2009.04.007 Palmer M, Moffat C, Saranzewa J, Harvey G, Wright A, Connolly CN (2013) Cholinergic pesticides cause mushroom body neuronal inactivation in honeybees. Nat. Commun. 4: 1634 Pham-Delègue MH, Decourtye A, Kaiser L, Devillers J (2002). Behavioural methods to assess the effects of pesticides on honey bees. Apidologie 33(5): 425–432. Peng T, Xu Y, Zhang Y (2018) Comparative genomics of molybdenum utilization in prokaryotes and eukaryotes. BMC Genomics 19: 691. https://doi.org/10.1186/s12864-018-5068-0 Pisa LW, Amaral-Rogers V, Belzunces LP, Bonmatin JM, Downs CA, Goulson D, Kreutzweiser DP, Krupke C, Liess M, Mcfield M, Morrisey CA, Noome DA, Settele J, Simon-Delso N, Stark JD, Van Der Sluijs JP, Van Dyck H, Wiemers M (2015) Effects of neonicotinoids and fipronil on non-target invertebrates. Environmental Science and Pollution Research. 22(1): 68–102. DOI 10.1007/s11356-014-3471-x . Pisa L, Goulson D, Yang EC, Gibbons D, Sánchez-Bayo F, Mitchell E, Aebi A, van der Sluijs J, MacQuarrie CJK, Giorio C, Yim Long E, McField M, Bijleveld van Lexmond M, Bonmatin JM (2021) An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 2: impacts on organisms and ecosystems. Environ Sci Pollut Res 28:11749–11797. DOI 10.1007/s11356-017-0341-3 Potts SG, Roberts SPM, Dean R, Marris G, Brown MA, Jones R, Neumann P, Settele J (2010) Declines of managed honey bees and beekeepers in Europe. J Apicult Res. 49(1), 15–22. Pudasaini, R. (2020) Behavioral changes due to sub-lethal doses of pesticides in bees. J. Entomol. 17, 84–92. Qiao D, Seidler FJ, Slotkin TA (2005) Oxidative mechanisms contributing to the developmental neurotoxicity of nicotine and chlorpyrifos. Toxicol. Appl. Pharm. 206(1), 17–26 Roat TC, Carvalho SM, Nocelli RCF, Silva-Zacarin ECM, Palma MS, Malaspina O (2013) Effects of Sublethal Dose of Fipronil on Neuron Metabolic Activity of Africanized Honeybees. Archives of Environmental Contamination and Toxicology 64(3): 456–466. DOI 10.1007/s00244-012-9849-1 . Sandoz, J.-C., 2011. Behavioral and Neurophysiological Study of Olfactory Perception and Learning in Honeybees. Frontiers in Systems Neuroscience 5. https://doi.org/10.3389/fnsys.2011.00098 Schwarz G, Mendel RR, Ribbe MW (2009) Molybdenum cofactors, enzymes and pathways. Nature 460, 839–847. https://doi.org/10.1038/nature08302 Simon-Delso N, Amaral-Rogers V, Belzunces LP, Bonmatin JM, Chagnon M, Downs C, Furlan L, Gibbons DW, Giorio C, Girolami V, Goulson D, Kreutzweiser DP, Krupke CH, Liess M, Long E, Mcfield M, Mineau P, Mitchell EAD, Morrisey CA, Noome DA, Pisa L, Settele J, Stark JD, Tapparo A, Van Dyck H, Van Praagh J, Van Der Sluijs JP, Whitehorn PR, Wiemers M (2015) Systemic insecticides (neonicotinoids and fipronil): trends, uses, mode of action and metabolites. Environmental Science and Pollution Research 22(1): 5–34. DOI 10.1007/s11356-014-3470-y . Siviter H, Koricheva J, Brown MJF, Leadbeater E (2018). Quantifying the impact of pesticides on learning and memory in bees. Journal of Applied Ecology 55(6): 2812–2821. Tingle CCD, Rother JA, Dewhurst CF, Lauer S, King WJ (2003) Fipronil: Environmental Fate, Ecotoxicology, and Human Health Concerns. In: WARE, George W. (ed.), Reviews of Environmental Contamination and Toxicology New York, NY: Springer New York. pp. 1–66. ISBN 978-1-4419-3033-0. http://link.springer.com/10.1007/978-1-4899-7283-5_1 Tsuruda JM, Chakrabarti P, Sagili RR (2021) Honey Bee Nutrition. Vet. Clin. North Am. Food Anim. Pract., Honey Bee Veterinary Medicine 37: 505–519. https://doi.org/10.1016/j.cvfa.2021.06.006 Van der Sluijs JP, Simon-Delso N, Goulson D, Maxim L, Bonmatin JM, Belzunces LP, (2013), Neonicotinoids, bee disorders and the sustainability of pollinator services. Current Opinion in Environmental Sustainability 5:293–305 Zhang G, Zhang W, Cui X, Xu B (2015) Zinc nutrition increases the antioxidant defenses of honey bees. Entomol. Exp. Appl. 156: 201–210. https://doi.org/10.1111/eea.12342 Additional Declarations Competing interest reported. One author (SF) is linked to a patent about the use of this family of complexes for the beekeeping industry (European Patent EP4185594B1 delivered on 4th december 2024). The authors declare these interests in the interest of full transparency and affirm that the reported findings are presented objectively and without bias. Supplementary Files MoNaPesticidesBiometalsSUPPORTINGINFORMATIONVf.docx Cite Share Download PDF Status: Posted Version 1 posted 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-8766031","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Short Report","associatedPublications":[],"authors":[{"id":587387256,"identity":"816c8075-936c-423d-a9ea-2bf83ac06dd8","order_by":0,"name":"Loïc Colin-Duchevet","email":"","orcid":"","institution":"Évolution, Génomes, Comportement, Écologie","correspondingAuthor":false,"prefix":"","firstName":"Loïc","middleName":"","lastName":"Colin-Duchevet","suffix":""},{"id":587387257,"identity":"c12b75d0-861f-45f4-9c55-ea803fd68cb9","order_by":1,"name":"Précillia Cochard","email":"","orcid":"","institution":"APINOV SAS","correspondingAuthor":false,"prefix":"","firstName":"Précillia","middleName":"","lastName":"Cochard","suffix":""},{"id":587387258,"identity":"1ee949ec-20da-40f6-bc0a-96ec1c2acdfc","order_by":2,"name":"Benjamin Poirot","email":"","orcid":"","institution":"APINOV SAS","correspondingAuthor":false,"prefix":"","firstName":"Benjamin","middleName":"","lastName":"Poirot","suffix":""},{"id":587387259,"identity":"327a005f-b97b-4d5f-b7b3-f8a3ade89292","order_by":3,"name":"Jean-Luc Brunet","email":"","orcid":"","institution":"INRAE","correspondingAuthor":false,"prefix":"","firstName":"Jean-Luc","middleName":"","lastName":"Brunet","suffix":""},{"id":587387260,"identity":"cb302025-0c25-4ab2-847c-6f2722fa4680","order_by":4,"name":"Jean-Christophe Sandoz","email":"","orcid":"","institution":"Évolution, Génomes, Comportement, Écologie","correspondingAuthor":false,"prefix":"","firstName":"Jean-Christophe","middleName":"","lastName":"Sandoz","suffix":""},{"id":587387262,"identity":"6d875e0d-1f36-4ac8-96f7-fd46e97926dc","order_by":5,"name":"Sébastien Floquet","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABD0lEQVRIie3PMWuDQBTA8SdCsryQ9YklfoWTg6QlgX6VCwW7SCGLYyIUdLF7t34FP8LJDV2sc7uldM2QbrpVbVMK5eza4f5w5yn+4B2AyfQvw26jdlmvsv8wjvvHdJiIjtisJ4if0omHCfwgJIaJl94V7019PluADfIYqdmlc5g7dQS00BhWVlcuCuIXsQ3FfaU4uuHcxQroTGoIhcxt77LO5VSqSaLWmRtybiWwJd1gDwfe1IJ2ubShI7vMKbnfJEA6As84p3Ywwb6IQEJ/PxkgrLwJlhiQn6v+Ltd+VgabN6xIS7z0Sb3Uq63HHm+t/TFaeuNU5UUdrfSDfWd32+j0NvobnP78dTCZTCYTfABKFVOC9TwTwAAAAABJRU5ErkJggg==","orcid":"","institution":"Institut Lavoisier de Versailles","correspondingAuthor":true,"prefix":"","firstName":"Sébastien","middleName":"","lastName":"Floquet","suffix":""}],"badges":[],"createdAt":"2026-02-02 14:23:23","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8766031/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8766031/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":102201332,"identity":"b5e69edc-2f2f-49cb-a89e-f93744056216","added_by":"auto","created_at":"2026-02-09 11:00:24","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":103715,"visible":true,"origin":"","legend":"\u003cp\u003eStructural representation of the complex [Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e(EDTA)]\u003csup\u003e2-\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8766031/v1/fd1b3d689a673d0eed5f20b3.png"},{"id":102201333,"identity":"dc149acd-1718-484b-a05c-2a9009b4fce9","added_by":"auto","created_at":"2026-02-09 11:00:24","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":632816,"visible":true,"origin":"","legend":"\u003cp\u003eConditioning of the proboscis extension response (PER). (A) Views of the harnessing tubes used in this experiment; (B) View of the experimental device: An odour stimulation device producing a constant air flow of 3.5 L/min is send to a bee immobilized in a tube; (C) schematic representation of the procedure followed for PER test; (D) Learning curves (%PER) of bees during 5-trial absolute conditioning after different treatments: fipronil was applied or not on bees that received a chronic Mo treatment (“Mo only” and “fipronil + Mo” groups respectively) or on control bees that received or no Mo treatment (“control” and “fipronil” groups respectively) ; (E) Results obtained for retention tests performed 1 hour after conditioning for both the conditioned odor (CS) and the new non learned odor (NoD). Different letters indicate significant differences in posthoc tests (P\u0026lt;0.05).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8766031/v1/23c81eee618101f3ae7c5edb.png"},{"id":102201335,"identity":"9e92a1bc-ba6f-49d7-9839-df7afec7468c","added_by":"auto","created_at":"2026-02-09 11:00:24","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":83898,"visible":true,"origin":"","legend":"\u003cp\u003eKaplan-Meier survival curve for each treatment (“Control”, “Pesticides” and “Pesticides+Mo” groups)\u003cem\u003e.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8766031/v1/0a85250a4140c6102d0bd906.png"},{"id":107706985,"identity":"2a235692-17a5-4132-a29b-d1f2077d2803","added_by":"auto","created_at":"2026-04-24 09:19:12","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1184298,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8766031/v1/77d53a60-5547-40f2-9f42-92779b43c833.pdf"},{"id":102201334,"identity":"2569e752-402e-4378-b559-02a50808c328","added_by":"auto","created_at":"2026-02-09 11:00:24","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":1714403,"visible":true,"origin":"","legend":"","description":"","filename":"MoNaPesticidesBiometalsSUPPORTINGINFORMATIONVf.docx","url":"https://assets-eu.researchsquare.com/files/rs-8766031/v1/b40141a97db670f3449eabd5.docx"}],"financialInterests":"Competing interest reported. One author (SF) is linked to a patent about the use of this family of complexes for the beekeeping industry (European Patent EP4185594B1 delivered on 4th december 2024). The authors declare these interests in the interest of full transparency and affirm that the reported findings are presented objectively and without bias.","formattedTitle":"A molybdenum coordination complex that enables honey bees to mitigate the sublethal toxic effects of fipronil","fulltext":[{"header":"Full Text","content":"\u003cp\u003eBees provide a vital ecosystem service thanks to their contribution to the maintenance of biodiversity and food production (van der Sluijs et al. 2013). Among the wide variety of bee species, the managed honey bees \u003cem\u003eApis mellifera\u003c/em\u003e play a key role in insect-mediated pollination, while about 80% of all cultivated plant species and 40% of our diet directly depend on pollination (Klein et al., 2007; Aizen et al., 2009). However, \u003cem\u003eApis mellifera\u003c/em\u003e is gravely endangered by colony losses (Potts at al. 2010; Bruckner et al., 2023; Gray et al., 2023; Benito-Murcia et al. 2025), which have dramatically increased in the last decades through a multifactorial process involving biological agents, a lack of resources (Naug, 2009; Tsuruda et al., 2021) and the use of pesticides (Goulson 2015). In this context, the development of new solutions to strengthen bees\u0026rsquo; health is of great interest.\u003c/p\u003e\n\u003cp\u003ePesticides are one of the major drivers behind the recent decline in pollinator populations (Bonmatin et al. 2015; Pisa et al. 2015; Simon-Delso et al. 2015; Giorio et al. 2021; Pisa et al. 2021). Pesticide usage associated with intensive agriculture can have detrimental impacts on honey bees ranging from immediate mortality to sub-lethal effects. The latter are more difficult to demonstrate but they can induce cognitive anomalies in honey bees notably through effects on learning performances, olfaction, visual ability, flight and homing disruptions, and detrimental physiological alterations (Palmer et al. 2013; Fischer et al. 2014; Go\u0026ntilde;alons and Farina 2018; Chakrabarti et al. 2019; Pudasaini 2020; Kumar et al. 2022). Even if these effects do not directly cause the death of the honey bees and the immediate demise of their colonies, they may become have strong detrimental effects in time. For instance, foragers with memory, orientation and/or physiological impairments might fail to return to their hive, dying from hunger or cold (van der Sluijs et al., 2013).\u003c/p\u003e\n\u003cp\u003eFipronil is a systemic insecticide that belongs to the phenylpyrazole family and is one of the best-selling insecticide molecules in the world (Bonmatin et al. 2015). Due to its low median lethal dose (LD\u003csub\u003e50\u003c/sub\u003e) of around 6 ng/bee for acute topical application, fipronil is considered to be highly toxic to bees (European Food Safety Authority, 2013a). The scientific literature is rich in studies demonstrating the sublethal effects of this systemic insecticide on \u003cem\u003eApis mellifera\u0026nbsp;\u003c/em\u003e(Pisa et al. 2015) either by topical application, ingestion, or injection (Decourtye et al. 2005; El Hassani et al. 2005, 2009; Aliouane et al. 2008; Bernadou et al. 2009;). It acts on GABA receptors, which are highly present in the bee brain and are known to play a key role in learning and memory processes, and causes abnormal nervous system activity, convulsions, and death (Tingle et al. 2003; El Hassani et al. 2005, 2009; Holder et al. 2018).\u003c/p\u003e\n\u003cp\u003eGiven its toxicity to honeybees, fipronil has been banned in agriculture in France since 2004, but its use is still permitted for treatment against fleas and ticks on pets and against termites due to its lower toxicity to vertebrates. Furthermore, since it is not efficiently removed by conventional water treatment facilities and has a relatively long half-life time in soils ranging from 100 to 200 days depending on climatic conditions (Bonmatin 2015), it is relatively persistent in the environment, particularly in water and pollen consumed by bees. Therefore, even at low concentration these insecticides pose serious risks of undesirable environmental impacts (Simon-Delso et al. 2015) and honey bees can be exposed to potential sublethal doses of fipronil even in countries where this molecule has been banned from agriculture.\u003c/p\u003e\n\u003cp\u003eQuality nutrition is one way to improve honey bee health, reduce mortality (Alaux et al., 2010; Dolezal et al., 2019) and mitigate the effects of other stressors such as pesticides (Castle et al., 2022). However, optimizing bee nutrition requires achieving the right balance between macronutrients and micronutrients, a process that is not always straightforward (Bonoan et al., 2018; Lau et al., 2023). To overcome nutritional limitations, beekeepers rely on feed supplements usually in the form of sugar syrup and fondants, sometimes supplemented with proteins and micronutrients including vitamins and minerals (Lau et al., 2023). Among minerals, trace elements (TE) undoubtedly play a key role, as they are involved in a wide variety of biochemical processes. Honey bees\u0026rsquo; needs in TE are met by pollen and water (Bonoan et al., 2018), two sources of TE which however strongly vary among flower species (Bay et al., 2021), environment and climatic conditions across space and time. Surprisingly, however, studies on the importance and needs of TE for honey bee health remain scarce (Herbert, 1979; Zhang et al., 2015).\u003c/p\u003e\n\u003cp\u003eMolybdenum (Mo) is a trace element that plays an essential role in all living organisms (Hill 2002; Mendel 2012), including insects (Dow, 2017). It is involved in a wide variety of enzymes which play a crucial role in the catalysis of redox reactions (Hille, 2002; Schwarz et al., 2009). In eukaryotes, these enzymes mainly belong to the sulfite oxidase (SO) and xanthine oxidase (XO) families (Peng et al., 2018), which are useful for the degradation of xenobiotics with a broad substrate spectrum. In insects, this enzyme mainly exists in the form of xanthine dehydrogenase (XDH), which can be converted into XO under oxidative stress which can be induced by pesticides through the formation of reactive oxygen species (ROS) (Qiao et al. 2005; Chakrabarti et al. 2015).\u003c/p\u003e\n\u003cp\u003eHoney bees naturally contain the Mo trace element at an average level of about 0.4 ppm (Fuior et al. 2025), but its role for honey bee health remains unknown to date. Very recently however, Fuior et al. (2025) and Benito-Murcia et al. (2025) evidenced that \u003cstrong\u003eNa\u003csub\u003e2\u003c/sub\u003e[Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e(EDTA)]\u003c/strong\u003e (Figure 1), a coordination complex of Mo(+V) belonging to a wide family of [Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003eE\u003csub\u003e2\u003c/sub\u003e]\u003csup\u003e2+\u003c/sup\u003e-based complexes (E = S or O) displaying various biological properties (Fuior et al. 2022; Gretarsdottir et al. 2022), can be efficient as feed supplement to improve the honey bee health.\u003c/p\u003e\n\u003cp\u003eIndeed, feeding beehives with only a few milligrams of this complex, hereafter referred to as \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u003c/strong\u003e, diluted in a sugar syrup (at 0.2 to 2 mg/L) showed prolonged positive effects on the colonies. \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u003c/strong\u003e is assimilated by honey bees in both field and laboratory conditions and does not exhibit any toxicity on honey bees even in case of overdosage. It provokes an increase of the anti-oxidative properties of hemolymph, can induce an increase in honey production up to 49% and a decrease in winter mortality by 44%. Moreover, Fuior et al. (2025) evidenced that feeding bees in laboratory conditions with the complex produces an increase in Mo content in the head and especially in the brain and in the neurolemma, a protective membrane around the brain, which already naturally contain Mo at a low level.\u003c/p\u003e\n\u003cp\u003eThe question therefore naturally arises as to whether this load in molybdenum in and around the brain could protect honeybees from the deleterious effects of a systemic insecticide such as fipronil, which is known to have a significant adverse impact on bees\u0026rsquo; cognitive performances. The main objective of this study was thus to determine whether the \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u0026nbsp;\u003c/strong\u003ecomplex could have beneficial effects on bees exposed to a topical fipronil treatment, either on its survival face with a lethal dose of fipronil or on its learning performances when treated with sublethal doses of fipronil.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe first part of this communication aims to address this issue while a second part aims investigate if the results obtained with fipronil are specific to this pesticide or could be extended to other chemicals the honey bees could meet in nectar. A first evaluation of the level of xanthine oxidase enzyme, an enzyme potentially representative of molybdenum-dependent oxidase enzymes modulation and related to the level of pesticides (Chakrabarti et al. 2015) is also investigated.\u003c/p\u003e\n\u003cp\u003eIn order to assess whether molybdenum treatment could reduce the sensitivity of bees to fipronil exposure, two groups of 300 bees isolated upon emergence were divided into groups of 30 in Pain-type Plexiglas cages (see Figure S2, SI) and placed in an oven at 35\u0026deg;C and 50% humidity. In the control group, bees were fed during 8 days with sucrose solution (50% w/w), water and pollen \u003cem\u003ead libitum\u003c/em\u003e. After 8 days, only water and sugar solution were provided, still \u003cem\u003ead libitum\u003c/em\u003e. In the fipronil groups, sucrose solution was supplemented with \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u0026nbsp;\u003c/strong\u003eat 20 mg/L for the whole duration of feeding. The bees were used in the experiment 14 days after emergence, because worker bees typically become foragers and express strong learning abilities at this age. The bees were first narcotized inside a CO\u003csub\u003e2\u003c/sub\u003e chamber at 10\u0026deg;C (Fig S3A, SI), placed on an ice bed (Fig S3B, SI) and 1 \u0026micro;L of solution of fipronil at 0, 3, 6, 12 or 24 ng/\u0026micro;L in acetone 0.1% in water was applied onto the dorsal part of the thorax. After exposure, the bees were returned to their cage and maintained at 35\u0026deg;C and 50% relative humidity. Two replicates of 30 bees were prepared for each treatment and mortality was recorded at 4, 24 and 48 hours after exposure. The resulting dose-response curves show bees\u0026rsquo; mortality rate as a function of the dose of fipronil received (see Fig S4, SI). The curves are very similar for the two groups, which indicates that molybdenum feeding had no impact on honeybee mortality with increasing doses of fipronil. The LD\u003csub\u003e50\u003c/sub\u003e were 5.97 ng/bee and 5.49 ng/bee for molybdenum-treated and control bees respectively, values that are close to that measured (5.93 ng/bee) by European Food Safety Authority (2013b). The difference between the 2 treatments was not significant (t-test, p = 0.49). Likewise, no difference appeared in the slope of the curve (t-test, p = 0.68). Therefore, no significant effects of \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u003c/strong\u003e treatment was found on bees\u0026rsquo; resistance to lethal fipronil treatment.\u003c/p\u003e\n\u003cp\u003eNext, we asked if molybdenum treatment could protect bees from the deleterious effects of a sublethal dose of fipronil on bees\u0026rsquo; learning performances. The dose of 0.5 ng fipronil per bee was chosen. To do so, bees were subjected to an associative learning task using the conditioning of the proboscis extension reflex (PER), which is known to be a relevant tool to estimate the side effects of stressors on honey bees, in particular pesticides (Pham-Del\u0026egrave;gue et al. 2002; Giurfa and Sandoz, 2012; Siviter et al., 2018). In this protocol, restrained bees learn to associate an odorant (conditioned stimulus, CS) with a sucrose reward (unconditioned stimulus, US), an association that bees typically form in nature while foraging for nectar (Menzel, 1999; Sandoz, 2011). Two groups of 32-34 bees isolated at emergence were prepared as described above: one control group and one test group fed with \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u003c/strong\u003e at 20 mg/L in sucrose syrup (50% w/w). After 14 days, the bees were narcotized with CO\u003csub\u003e2\u003c/sub\u003e, and each group was split into two experimental groups: one receiving 1 \u0026micro;L of acetone 0.1% in water; one receiving 0.5 ng/bee of fipronil in 1 \u0026micro;L acetone 0.1% in water, in all cases 4 h before performing olfactory conditioning experiments. Four experimental groups were thus constituted as follows:\u003c/p\u003e\n\u003cul class=\"decimal_type\"\u003e\n \u003cli\u003eOne group of 34 bees fed with sucrose only on which 1 \u0026micro;L of acetone 0.1% in water was applied onto the thorax (\u0026ldquo;control\u0026rdquo; group);\u003c/li\u003e\n \u003cli\u003eOne group of 32 bees fed with sucrose supplemented with \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u003c/strong\u003e at 20 mg/L on which 1 \u0026micro;L of acetone 0.1% was applied onto the thorax (\u0026ldquo;Mo only\u0026rdquo; group)\u003c/li\u003e\n \u003cli\u003eOne group of 32 bees fed with sucrose only on which 0.5 ng of fipronil in 1 \u0026micro;L of acetone 0.1% was applied onto the thorax (\u0026ldquo;fipronil\u0026rdquo; group)\u003c/li\u003e\n \u003cli\u003eOne group of 34 bees fed with sucrose supplemented with \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u003c/strong\u003e at 20 mg/L on which 0.5 ng of fipronil in 1 \u0026micro;L of acetone 0.1% was applied onto the thorax (\u0026ldquo;fipronil + Mo\u0026rdquo; group).\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003eFigure 2 shows the experimental setup used for the PER tests (Figures 2A and 2B) and the procedure followed for the PER experiment (Figure 2C). The results of the olfactory conditioning procedure performed through 5 successive trials, in which\u003cem\u003e\u0026nbsp;\u003c/em\u003ebees associate an olfactory stimulus (CS = 1-hexanol or 1-nonanol) with a sucrose reward (US) are represented in Figure 2D. The olfactory stimulus used as CS (1-hexanol or 1-nonanol) did not influence bees\u0026rsquo; learning performances (GLMM, stimulus effect, \u0026chi;\u003csup\u003e2\u003c/sup\u003e = 0.0072, 1 df, p = 0.93) so that data with both odorants were pooled (raw data are given in the SI).\u003c/p\u003e\n\u003cp\u003eFigure 2D shows that bees learned the CS-US association (GLMM, trials effect, \u0026chi;\u003csup\u003e2\u003c/sup\u003e = 11.5, 4 df, p = 0.02). In addition, treatments had a significant effect on learning performances (GLMM, trials effect, \u0026chi;\u003csup\u003e2\u003c/sup\u003e = 11.3, 3 df, p = 0.01). In the control group, bees showed typical learning performances and 81.5% responded to the CS at the 5\u003csup\u003eth\u003c/sup\u003e trial. Fipronil presented alone strongly and significantly reduced bees\u0026rsquo; ability to associate the odour with the sucrose reward compared with control bees. Only 52% of bees responded to the CS at the end of training for a dose of fipronil less than 10 times lower that the lethal dose, a proportion significantly lower than for the control group while (Tukey contrasts, corrected p = 0.041). On the contrary, in bees that received \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u003c/strong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003etreatment (group \u0026ldquo;fipronil+Mo\u0026rdquo;), fipronil had no such effect and all bees showed good learning performances, reaching the same performance level as control bees (Tukey contrasts, corrected p = 1). Finally, \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u003c/strong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003etreatment alone had no effect on bees\u0026rsquo; learning performance, as shown by the lack of difference between the two groups that received no fipronil (Tukey contrasts, corrected p = 1). Furthermore, the protective effect of Mo can be seen in the significant difference between the \u0026ldquo;Fipronil\u0026rdquo; and \u0026ldquo;Mo+Fipronil\u0026rdquo; groups (Tukey contrasts, corrected p = 0.041). We conclude that feeding bees with the complex \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u0026nbsp;\u003c/strong\u003ewas able to mitigate the negative impact of a sublethal dose of fipronil on bees\u0026rsquo; associative learning performances.\u003c/p\u003e\n\u003cp\u003eOne hour after conditioning, two retention tests were performed, one with the learned odorant (CS, 1-hexanol or 1-nonanol) and the second with a novel odorant (NoD). This last test shown in Figure 2E, allowed to determine if the association learned during the acquisition phase was specific for the CS. In retention tests performed 1h after training, the same general pattern of results was observed. Treatment significantly influenced responses to the CS (Fisher\u0026rsquo;s exact test, p = 0.04). Pairwise comparisons revealed that the \u0026ldquo;fipronil\u0026rdquo; group that did not receive any \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u0026nbsp;\u003c/strong\u003etreatment, fipronil application significantly reduced bees\u0026rsquo; responses to the CS compared to the control group (Fisher\u0026rsquo;s exact test, corrected p = 0.036). On the contrary, in groups that received \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u003c/strong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003etreatment, the same level of responses was observed with or without fipronil application (Fisher\u0026rsquo;s exact test, p \u0026gt; 0.8). The proportion of bees responding to the NoD was smaller or equal to 3% in all groups. Bees responded significantly more to the CS than to the NoD in all groups (Mc Nemar test, p \u0026lt; 0.042). These results show that memory was specific to the CS, even in groups in which performances were impaired by fipronil application.\u003c/p\u003e\n\u003cp\u003eThis experiment unambiguously demonstrates that dietary treatment with the complex \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u003c/strong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003ein a sucrose syrup does not impair honey bees\u0026rsquo; olfactory learning abilities, but rather protects them from the deleterious effect of fipronil applied at a sublethal dose. We thus conclude that \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u003c/strong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003ecould help protect beehives from the threats posed by pesticide exposure, here fipronil.\u003c/p\u003e\n\u003cp\u003eFipronil is one pesticide among many others, and one may wonder whether this protection is specific to fipronil or can extends to other chemicals to which bees are exposed in nature. To address this question two groups of honey bees were intoxicated by ingestion of a cocktail of chemicals containing two fungicides, one insecticide and one chemical used to enhance the insecticidal properties, i.e. imoxystrobine, spiroxamine, phosmet and piperonylbutoxide respectively. These chemicals are known to be toxic for honey bees and are frequently detected in nectar of different flowers (Hayat et al. 2018, Azpiazu et al. 2019). A mixture of these molecules was diluted in Apistar\u0026copy; sugar syrup, following field realistic concentrations found in the literature: 10 \u0026micro;g/L imoxystrobine, 10 \u0026micro;g/L spiroxamine, 10 \u0026micro;g/L phosmet and 10 \u0026micro;g/L piperonylbutoxide. The two groups were constituted of 64 honey bees spread in 4 boxes containing 16 bees each. The first group called \u0026ldquo;pesticides\u0026rdquo; was fed ad libitum with sugar syrup containing the cocktail of chemicals, while the second group \u0026ldquo;pesticides+Mo\u0026rdquo; was fed \u003cem\u003ead libitum\u003c/em\u003e with sugar syrup containing the cocktail of chemicals and the \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u003c/strong\u003e complex at 2 mg/L, a concentration recently used in field test campaigns (Benito-Murcia et al. 2025). For comparison, a \u0026ldquo;control\u0026rdquo; group was constituted with 60 honey bees distributed in 3 boxes and fed with sugar syrup.\u003c/p\u003e\n\u003cp\u003eFor each group, bee mortality was registered every 2-3 days during 28 days. Survival curves using the Kaplan-Meier method were constructed for each treatment (Figure 3). Pairwise comparisons by Log-Rank tests show significant differences between \u0026ldquo;pesticides\u0026rdquo; and \u0026ldquo;Control\u0026rdquo; groups (p\u003csub\u003evalue\u003c/sub\u003e ˂ 0.0001) and between \u0026ldquo;pesticides\u0026rdquo; and \u0026ldquo;pesticides + Mo\u0026rdquo; groups ((p\u003csub\u003evalue\u003c/sub\u003e ˂ 0.0001). There was however no significant difference between \u0026ldquo;Control\u0026rdquo; and \u0026ldquo;pesticides+Mo\u0026rdquo; groups (p\u003csub\u003evalue\u003c/sub\u003e = 0.83529), despite the presence of the mixtures of toxic chemicals. This result suggests that the ingestion of the \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u003c/strong\u003e at 2 mg/L together with the pesticide cocktail in the sugar syrup balanced the negative impact of the latter and suggests that feeding honey bees with \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u003c/strong\u003e in syrup could protect bees from various pesticides.\u003c/p\u003e\n\u003cp\u003eThe mode of action of \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u003c/strong\u003e is currently unknown. Regulation of detoxifying molybdenum enzymes such as XO is appealing. As preliminary results, the level of XO was determined at different times in abdomen, where the expression of XO is higher, for the three previous groups of honey bees and an additional group constituted by some bees only fed with \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u003c/strong\u003e in syrup (see SI for more details). The number of bees was too limited to get statistically robust conclusions (8 or 9 per group). Nevertheless, at D15 (Figure S7, SI), the level of XO is decreased from control groups to \u0026ldquo;pesticides\u0026rdquo; group (p = 0.052), while the level XO for the group fed with \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u003c/strong\u003e only (\u0026ldquo;Mo-only\u0026rdquo;) seems intermediate, suggesting that the antioxidative properties of \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u003c/strong\u003e (Fuior et al 2025) could reduce the oxidative stress and thus this level (Chakrabarti et al 2015). Interestingly the level of XO for the group \u0026ldquo;pesticides + Mo\u0026rdquo; is found equivalent to that of the group \u0026ldquo;Mo-only\u0026rdquo;. This first result is in line with previous results showing the \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u003c/strong\u003e mitigate the impact of pesticides in honey bees and suggest that this complex could regulate the level of the XO enzyme. Further investigations are needed on XO and other molybdo-enzymes at different times, different dosages of Mo-complex, and different parts of the bees, notably in the head to conclude on this hypothesis.\u003c/p\u003e\n\u003cp\u003eIn conclusion, this study demonstrates that feeding honeybees with sugar syrup enriched with \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u003c/strong\u003e coordination complex could help protect honey bee colonies from threats related to pesticide exposure. In particular, we have shown that \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u0026nbsp;\u003c/strong\u003ecan compensate for the negative sublethal effects of fipronil on honey bees\u0026rsquo; cognitive abilities or on mortality induced by the ingestion of a cocktail of chemicals that they may encounter in nature. The mode of action of the complex remains unknown, but its antioxidant properties and its role in regulating xanthine oxidase (as well as xanthine dehydrogenase XDH) may be suggested. These results pave the way for further studies aimed at understanding the mode of action of \u003cstrong\u003eNa-Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-EDTA\u0026nbsp;\u003c/strong\u003eand developing new complexes of molybdenum and other transition metals to protect honeybees from chemicals present in the environment.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOne author (SF) is linked to a patent about the use of this family of complexes for the beekeeping industry (European Patent EP4185594B1 delivered on 4\u003csup\u003eth\u003c/sup\u003e december 2024). The authors declare these interests in the interest of full transparency and affirm that the reported findings are presented objectively and without bias.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eUniversity of Versailles, INRAE and the CNRS are gratefully acknowledged for financial support. This work was funded by “lune de miel” foundation, the CNRS MITI (call Metallomix, project “MOLYBEE”), and the SATT Paris-Saclay (project APIMONA).\u0026nbsp;\u003c/p\u003e\n\u003ch3\u003e\u003cstrong\u003eSupplementary Information (SI) / data availability\u003c/strong\u003e\u003c/h3\u003e\n\u003cp\u003eThe supporting information (SI) contains all details concerning materials and methods. The raw data have been deposited on Mendeley data and are accessible through the link https://data.mendeley.com/preview/vg8bcz44j4?a=92fd174c-0730-48dc-9703-0ece02a96b17\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contribution statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFipronil experiments: L.C.; mortality test with a cocktail of pesticides: P.C., B.P.; Xanthine Oxidase mesurements: J.-L.B; Methodology: J.-C.S, B.P. J.-L. B., S.F.; Formal Analysis, L.C., P.C., J.-L.B; Writing-Review and Editing, J.-C. S. and S.F. All authors have read and agreed to the published version of the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAizen MA, Garibaldi LA, Cunningham SA, Klein AM (2009) How much does agriculture depend on pollinators? Lessons from long-term trends in crop production. Ann. Bot. 103: 1579\u0026ndash;1588. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1093/aob/mcp076\u003c/span\u003e\u003cspan address=\"10.1093/aob/mcp076\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlaux C, Ducloz F, Crauser D, Le Conte Y (2010) Diet effects on honeybee immunocompetence. Biol. Lett. 6: 562\u0026ndash;565. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1098/rsbl.2009.0986\u003c/span\u003e\u003cspan address=\"10.1098/rsbl.2009.0986\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAliouane Y, El Hassani AK, Gary V, Armengaud C, Lambin M, Gauthier M (2009) Subchronic exposure of honeybees to sublethal doses of pesticides: effects on behavior. Environmental Toxicology and Chemistry 28(1): 113. DOI \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1897/08-110.1\u003c/span\u003e\u003cspan address=\"10.1897/08-110.1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAzpiazu, C, Bosch J, Vi\u0026ntilde;uela E, Medrzycki P, Teper D, Sgolastra F (2019) Chronic oral exposure to field-realistic pesticide combinations via pollen and nectar: effects on feeding and thermal performance in a solitary bee. Sci Rep. 9: 13770\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBay V, Topal E, \u0026Ccedil;akıcı N, Yıldızdal İ, Tosunoglu A (2021) Palynological analyses, chemical and mineral composition of some honeybee pollen pellets. Uludağ Arıcılık Derg. 21, 187\u0026ndash;197. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.31467/uluaricilik.996036\u003c/span\u003e\u003cspan address=\"10.31467/uluaricilik.996036\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBenito-Murcia M, Riva C, Garc\u0026iacute;a-Vicente EJ, P\u0026eacute;rez A, Dom\u0026iacute;nguez MM, Hermosilla N, Cochard P, Hatjina F, Holmiere M, Mart\u0026iacute;nez-Morcillo S, Risco D, Floquet S. (2025) Reducing honey bee winter mortality with molybdenum supplementation: field evidence across Europe. Research in Veterinary Science, 197: 105932. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1101/2025.07.23.666091\u003c/span\u003e\u003cspan address=\"10.1101/2025.07.23.666091\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBernadou A, D\u0026eacute;mares F, Couret-Fauvel T, Sandoz JC, Gauthier M (2009) Effect of fipronil on side-specific antennal tactile learning in the honeybee. Journal of Insect Physiology 55(12): 1099\u0026ndash;1106. DOI \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.jinsphys.2009.08.019\u003c/span\u003e\u003cspan address=\"10.1016/j.jinsphys.2009.08.019\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBonmatin JM, Giorio C, Girolami V, Goulson D, Kreutzweiser DP, Krupke C, Liess M, Long E, Marzaro M, Mitchell EAD, Noome DA, Simon-Delso N, Tapparo A (2015) Environmental fate and exposure; neonicotinoids and fipronil. Environ Sci Pollut Res 22:35\u0026ndash;67, DOI \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s11356-014-3332-7\u003c/span\u003e\u003cspan address=\"10.1007/s11356-014-3332-7\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBonoan RE, O\u0026rsquo;Connor LD, Starks PT (2018) Seasonality of honey bee (Apis mellifera) micronutrient supplementation and environmental limitation. J. Insect Physiol. 107:23\u0026ndash;28.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBruckner S, Wilson M, Aurell D, Rennich K, vanEngelsdorp D, Steinhauer N, Williams GR (2023). A national survey of managed honey bee colony losses in the USA: results from the Bee Informed Partnership for 2017\u0026ndash;18, 2018\u0026ndash;19, and 2019\u0026ndash;20. J. Apic. Res. 62: 429\u0026ndash;443. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/00218839.2022.2158586\u003c/span\u003e\u003cspan address=\"10.1080/00218839.2022.2158586\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCastle D, Alkassab AT, Bischoff G, Steffan-Dewenter I, Pistorius J (2022) High nutritional status promotes vitality of honey bees and mitigates negative effects of pesticides. Sci. Total Environ. 806, 151280. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.scitotenv.2021.151280\u003c/span\u003e\u003cspan address=\"10.1016/j.scitotenv.2021.151280\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChakrabarti P, Rana S, Sarkar S, Smith B, Basu P (2015) Pesticide-induced oxidative stress in laboratory and field populations of native honey bees along intensive agricultural landscapes in two Eastern Indian states., Apidologie, 46: 107\u0026ndash;129\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChakrabarti, P., Sarkar, S., Basu, P. (2019) Pesticide induced visual abnormalities in Asian honey bees\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e(Apis cerana L.) in intensive agricultural landscapes. Chemosphere. 230: 51\u0026ndash;58\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDecourtye A, Devillier J, Genecque E, Le Menach K, Budzinski H, Cluzeau S, Pham-Del\u0026egrave;gue MH (2005) Comparative Sublethal Toxicity of Nine Pesticides on Olfactory Learning Performances of the Honeybee Apis mellifera. Archives of Environmental Contamination and Toxicology 48(2): 242\u0026ndash;250. DOI \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s00244-003-0262-7\u003c/span\u003e\u003cspan address=\"10.1007/s00244-003-0262-7\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDolezal AG, Carrillo-Tripp J, Judd TM, Allen Miller W, Bonning BC, Toth AL (2019) Interacting stressors matter: diet quality and virus infection in honeybee health. R. Soc. Open Sci. 6, 181803. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1098/rsos.181803\u003c/span\u003e\u003cspan address=\"10.1098/rsos.181803\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDow JA (2017) The essential roles of metal ions in insect homeostasis and physiology. Curr. Opin. Insect Sci. 23: 43\u0026ndash;50.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEl Hassani AK, Dacher M, Gauthier M, Armengaud C (2005) Effects of sublethal doses of fipronil on the behavior of the honeybee (Apis mellifera). Pharmacology Biochemistry and Behavior 82(1): 30\u0026ndash;39. DOI \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.pbb.2005.07.008\u003c/span\u003e\u003cspan address=\"10.1016/j.pbb.2005.07.008\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEl Hassani AK, Dupuis JP, Gauthier M, Armengaud C (2009) Glutamatergic and GABAergic effects of fipronil on olfactory learning and memory in the honeybee. Invertebrate Neuroscience 9(2): 91\u0026ndash;100. DOI \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s10158-009-0092-z\u003c/span\u003e\u003cspan address=\"10.1007/s10158-009-0092-z\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEuropean Food Safety Authority. (2013a) Guidance on the risk assessment of plant protection products on bees (Apis mellifera, Bombus spp. and solitary bees). EFSA Journal 11(7). DOI \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.2903/j.efsa.2013.3295\u003c/span\u003e\u003cspan address=\"10.2903/j.efsa.2013.3295\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEuropean Food Safety Authority. (2013b) Conclusion on the peer review of the pesticide risk assessment for bees for the active substance fipronil. EFSA Journal 11, 3158. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.2903/j.efsa.2013.3158\u003c/span\u003e\u003cspan address=\"10.2903/j.efsa.2013.3158\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFischer J, Mueller T, Spatz AK, Greggers U, Gruenewald B, Menzel R (2014) Neonicotinoids interfere with specific components of navigation in honeybees. PloS. One. 9(3), e91364\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFuior A, Hijazi A, Garbuz O, Bulimaga V, Zosim L, Cebotari D, Haouas M, Toderaş I, Gulea A, Floquet S (2022). Screening of biological properties of Mo\u003csup\u003eV\u003c/sup\u003e\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003e- and Mo\u003csup\u003eV\u003c/sup\u003e\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-based coordination complexes: Investigation of antibacterial, antifungal, antioxidative and antitumoral activities \u003cem\u003eversus\u003c/em\u003e growing of \u003cem\u003eSpirulina platensis\u003c/em\u003e biomass. J. Inorg. Biochem. 226, 111627. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jinorgbio.2021.111627\u003c/span\u003e\u003cspan address=\"10.1016/j.jinorgbio.2021.111627\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFuior A, Colin-Duchevet L, Cebotari V, No\u0026euml;l A, Ribaud I, G\u0026eacute;rard I, Garbuz O, Fregnaux M, L\u0026oacute;pez X, Larcher V, Shestopalov MA, Solovieva AO, Pozmogova TN, Gliga O, Railean N, Cochard P, Poirot B, Charistos L, Hatjina F, Somogyi A, Medjoubi K, Gaumer S, Gulea A, Toderas I, Sandoz JC, Floquet S (2025) Feed supplementation with molybdenum complexes improves honey bee health. Inorg. Chem. Front. 12: 7107\u0026ndash;7122.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGiorio C, Safer A, S\u0026aacute;nchez-Bayo F, Tapparo A, Lentola A, Girolami V, Bijleveld van Lexmond M, Bonmatin JM (2021) An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 1: new molecules, metabolism, fate, and transport. Environ Sci Pollut Res 28:11716\u0026ndash;11748 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11356-017-0394-3\u003c/span\u003e\u003cspan address=\"10.1007/s11356-017-0394-3\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGiurfa M, Sandoz JC (2012) Invertebrate learning and memory: Fifty years of olfactory conditioning of the proboscis extension response in honeybees. Learning \u0026amp; Memory 19(2):54\u0026ndash;66. DOI \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1101/lm.024711.111\u003c/span\u003e\u003cspan address=\"10.1101/lm.024711.111\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGo\u0026ntilde;alons CM, Farina WM (2018) Impaired associative learning after chronic exposure to pesticides in young adult honey bees. J. Exp. Biol. 221(7)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGoulson D, Nicholls E, Botias C, Rotheray EL (2015) Bee declines driven by combined stress from parasites, pesticides, and lack of flowers. Science, 347, 1255957.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGray A, Adjlane N, Arab A, Ballis A, Brusbardis V, Bugeja Douglas A, Cadah\u0026iacute;a L, Charri\u0026egrave;re JD, Chlebo, R, Coffey MF, Cornelissen B, Costa CAD, Danneels E, Danihl\u0026iacute;k J, Dobrescu C, Evans G, Fedoriak M, Forsythe I, Gregorc A, Ilieva Arakelyan I, Johannesen J, Kauko L, Kristiansen P, Martikkala M, Mart\u0026iacute;n-Hern\u0026aacute;ndez R, Mazur E, Medina-Flores CA, Mutinelli F, Omar EM, Patalano S, Raudmets A, San Martin G, Soroker V, Stahlmann-Brown P, Stevanovic J, Uzunov A, Vejsnaes F, Williams A, Brodschneider R (2023) Honey bee colony loss rates in 37 countries using the COLOSS survey for winter 2019\u0026ndash;2020: the combined effects of operation size, migration and queen replacement. J. Apic. Res. 62: 204\u0026ndash;210. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/00218839.2022.2113329\u003c/span\u003e\u003cspan address=\"10.1080/00218839.2022.2113329\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGretarsdottir JM, Lambert IH, Sturup S, Suman SG (2022) \u003cem\u003eIn Vitro\u003c/em\u003e Characterization of a Threonine-Ligated Molybdenyl-Sulfide Cluster as a Putative Cyanide Poisoning Antidote; Intracellular Distribution, Effects on Organic Osmolyte Homeostasis, and Induction of Cell Death. ACS Pharmac. Trans. Sci. 5(10): 907\u0026ndash;918.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHayat K, Afzal M, Aqueel MA, Khan QM (2018) Determination of Insecticide Residues in Fruits, Vegetables, Pollen, Nectar and Ground Water of Punjab (Pakistan). J. Agric. Res. 56:95\u0026ndash;105.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHerbert EW (1979) A New Ash Mixture for Honeybees Maintained on a Synthetic Diet. J. Apic. Res. 18, 144\u0026ndash;147. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/00218839.1979.11099958\u003c/span\u003e\u003cspan address=\"10.1080/00218839.1979.11099958\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHille R (2002) Molybdenum and Tungsten in Biology. Trends Biochem. Sci. 27 (7): 360\u0026ndash;367.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHolder PJ, Jones A, Tyler CR, Cresswell JE (2018) Fipronil pesticide as a suspect in historical mass mortalities of honey bees. Proceedings of the National Academy of Sciences 115 (51): 13033\u0026ndash;13038. DOI \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1073/pnas.1804934115\u003c/span\u003e\u003cspan address=\"10.1073/pnas.1804934115\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHosler, J.S., Buxton, K.L., Smith, B.H., 2000. Impairment of olfactory discrimination by blockade of GABA and nitric oxide activity in the honey bee antennal lobes. Behavioral Neuroscience 114, 514\u0026ndash;525. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1037/0735-7044.114.3.514\u003c/span\u003e\u003cspan address=\"10.1037/0735-7044.114.3.514\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKlein AM, Vaissiere BE, Cane JH, Steffan-Dewenter I, Cunningham SA, Krement C, Tscharntke T (2007) Importance of pollinators in changing landscapes for world crops. Proc. Biol. Sci. 274: 303\u0026ndash;313.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKumar D, Banerjee D, Chakrabarti P, Sarkar S, Basu P (2022) Oxidative stress and apoptosis in Asian honey bees (\u003cem\u003eA. cerana)\u003c/em\u003e exposed to multiple pesticides in intensive agricultural landscape. Apidologie 53: 25\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLau PW, Esquivel IL, Parys KA, Hung KLJ, Chakrabarti P (2023). The nutritional landscape in agroecosystems: a review on how resources and management practices can shape pollinator health in agricultural environments. Ann. Entomol. Soc. Am. 116: 261\u0026ndash;275.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMendel RR, Kruse T (2012) Cell biology of molybdenum in plants and humans. Biochimica et Biophysica Acta 1823: 1568\u0026ndash;1579.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMenzel, R., 1999. Memory dynamics in the honeybee. Journal of Comparative Physiology A 185, 323\u0026ndash;340. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s003590050392\u003c/span\u003e\u003cspan address=\"10.1007/s003590050392\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNaug D (2009) Nutritional stress due to habitat loss may explain recent honeybee colony collapses. Biol. Conserv. 142: 2369\u0026ndash;2372. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.biocon.2009.04.007\u003c/span\u003e\u003cspan address=\"10.1016/j.biocon.2009.04.007\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePalmer M, Moffat C, Saranzewa J, Harvey G, Wright A, Connolly CN (2013) Cholinergic pesticides cause mushroom body neuronal inactivation in honeybees. Nat. Commun. 4: 1634\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePham-Del\u0026egrave;gue MH, Decourtye A, Kaiser L, Devillers J (2002). Behavioural methods to assess the effects of pesticides on honey bees. Apidologie 33(5): 425\u0026ndash;432.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePeng T, Xu Y, Zhang Y (2018) Comparative genomics of molybdenum utilization in prokaryotes and eukaryotes. BMC Genomics 19: 691. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1186/s12864-018-5068-0\u003c/span\u003e\u003cspan address=\"10.1186/s12864-018-5068-0\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePisa LW, Amaral-Rogers V, Belzunces LP, Bonmatin JM, Downs CA, Goulson D, Kreutzweiser DP, Krupke C, Liess M, Mcfield M, Morrisey CA, Noome DA, Settele J, Simon-Delso N, Stark JD, Van Der Sluijs JP, Van Dyck H, Wiemers M (2015) Effects of neonicotinoids and fipronil on non-target invertebrates. Environmental Science and Pollution Research. 22(1): 68\u0026ndash;102. DOI \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s11356-014-3471-x\u003c/span\u003e\u003cspan address=\"10.1007/s11356-014-3471-x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePisa L, Goulson D, Yang EC, Gibbons D, S\u0026aacute;nchez-Bayo F, Mitchell E, Aebi A, van der Sluijs J, MacQuarrie CJK, Giorio C, Yim Long E, McField M, Bijleveld van Lexmond M, Bonmatin JM (2021) An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 2: impacts on organisms and ecosystems. Environ Sci Pollut Res 28:11749\u0026ndash;11797. DOI \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s11356-017-0341-3\u003c/span\u003e\u003cspan address=\"10.1007/s11356-017-0341-3\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePotts SG, Roberts SPM, Dean R, Marris G, Brown MA, Jones R, Neumann P, Settele J (2010) Declines of managed honey bees and beekeepers in Europe. J Apicult Res. 49(1), 15\u0026ndash;22.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePudasaini, R. (2020) Behavioral changes due to sub-lethal doses of pesticides in bees. J. Entomol. 17, 84\u0026ndash;92.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQiao D, Seidler FJ, Slotkin TA (2005) Oxidative mechanisms contributing to the developmental neurotoxicity of nicotine and chlorpyrifos. Toxicol. Appl. Pharm. 206(1), 17\u0026ndash;26\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRoat TC, Carvalho SM, Nocelli RCF, Silva-Zacarin ECM, Palma MS, Malaspina O (2013) Effects of Sublethal Dose of Fipronil on Neuron Metabolic Activity of Africanized Honeybees. Archives of Environmental Contamination and Toxicology 64(3): 456\u0026ndash;466. DOI \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s00244-012-9849-1\u003c/span\u003e\u003cspan address=\"10.1007/s00244-012-9849-1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSandoz, J.-C., 2011. Behavioral and Neurophysiological Study of Olfactory Perception and Learning in Honeybees. Frontiers in Systems Neuroscience 5. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3389/fnsys.2011.00098\u003c/span\u003e\u003cspan address=\"10.3389/fnsys.2011.00098\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSchwarz G, Mendel RR, Ribbe MW (2009) Molybdenum cofactors, enzymes and pathways. Nature 460, 839\u0026ndash;847. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1038/nature08302\u003c/span\u003e\u003cspan address=\"10.1038/nature08302\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSimon-Delso N, Amaral-Rogers V, Belzunces LP, Bonmatin JM, Chagnon M, Downs C, Furlan L, Gibbons DW, Giorio C, Girolami V, Goulson D, Kreutzweiser DP, Krupke CH, Liess M, Long E, Mcfield M, Mineau P, Mitchell EAD, Morrisey CA, Noome DA, Pisa L, Settele J, Stark JD, Tapparo A, Van Dyck H, Van Praagh J, Van Der Sluijs JP, Whitehorn PR, Wiemers M (2015) Systemic insecticides (neonicotinoids and fipronil): trends, uses, mode of action and metabolites. Environmental Science and Pollution Research 22(1): 5\u0026ndash;34. DOI \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s11356-014-3470-y\u003c/span\u003e\u003cspan address=\"10.1007/s11356-014-3470-y\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSiviter H, Koricheva J, Brown MJF, Leadbeater E (2018). Quantifying the impact of pesticides on learning and memory in bees. Journal of Applied Ecology 55(6): 2812\u0026ndash;2821.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTingle CCD, Rother JA, Dewhurst CF, Lauer S, King WJ (2003) Fipronil: Environmental Fate, Ecotoxicology, and Human Health Concerns. In: WARE, George W. (ed.), Reviews of Environmental Contamination and Toxicology New York, NY: Springer New York. pp. 1\u0026ndash;66. ISBN 978-1-4419-3033-0. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://link.springer.com/10.1007/978-1-4899-7283-5_1\u003c/span\u003e\u003cspan address=\"http://link.springer.com/10.1007/978-1-4899-7283-5_1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTsuruda JM, Chakrabarti P, Sagili RR (2021) Honey Bee Nutrition. Vet. Clin. North Am. Food Anim. Pract., Honey Bee Veterinary Medicine 37: 505\u0026ndash;519. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.cvfa.2021.06.006\u003c/span\u003e\u003cspan address=\"10.1016/j.cvfa.2021.06.006\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVan der Sluijs JP, Simon-Delso N, Goulson D, Maxim L, Bonmatin JM, Belzunces LP, (2013), Neonicotinoids, bee disorders and the sustainability of pollinator services. Current Opinion in Environmental Sustainability 5:293\u0026ndash;305\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang G, Zhang W, Cui X, Xu B (2015) Zinc nutrition increases the antioxidant defenses of honey bees. Entomol. Exp. Appl. 156: 201\u0026ndash;210. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/eea.12342\u003c/span\u003e\u003cspan address=\"10.1111/eea.12342\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Molybdenum, coordination complex, honey bee, pesticide, fipronil, olfactory learning","lastPublishedDoi":"10.21203/rs.3.rs-8766031/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8766031/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study deals with the effect of the molybdenum-based complex Na\u003csub\u003e2\u003c/sub\u003e[Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e(EDTA)] used as dietary supplement for the protection of honey bees \u003cem\u003eA. mellifera\u003c/em\u003e against deleterious effects of pesticides. Fipronil is a pesticide that is particularly toxic to bees,. In this study, we demonstrate that feeding bees in cages with a 20 mg/L complex solution in sucrose syrup does not significantly alter the value of this lethal dose. However, significant effects are observed at sublethal doses. When bees receive doses of 0.5 ng/bee of fipronil by contact, PER experiments show that their cognitive abilities are significantly reduced. In this study, we demonstrate that bees that have been pre-fed with Na\u003csub\u003e2\u003c/sub\u003e[Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e(EDTA)] are not affected by this decline in cognitive ability and that a protective effect is clearly evident. This effect is not specific to Fipronil. In fact, in the second part of this study, we show that bees that ingested a cocktail of four pesticides had a higher mortality rate than the control group, but that bees exposed to both this cocktail and the Mo-complex had a mortality rate comparable to that of the control group, thus demonstrating a more comprehensive protective effect. The regulation of molybdenum enzymes such as xanthine oxidase is one hypothesis to explain this effect. In the final part, preliminary results are presented to assess the impact of feeding with our complex on xanthine oxidase levels.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e","manuscriptTitle":"A molybdenum coordination complex that enables honey bees to mitigate the sublethal toxic effects of fipronil","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-09 11:00:08","doi":"10.21203/rs.3.rs-8766031/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"4d6b810d-07d3-4d37-98bc-6e460484b137","owner":[],"postedDate":"February 9th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-23T15:25:35+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-09 11:00:08","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8766031","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8766031","identity":"rs-8766031","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}