Assessing Invasion Intensity of the Yellow Crazy Ant (Anoplolepis gracilipes) Through Foraging Behaviour

Assessing Invasion Intensity of the Yellow Crazy Ant (Anoplolepis gracilipes) Through Foraging Behaviour | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Assessing Invasion Intensity of the Yellow Crazy Ant (Anoplolepis gracilipes) Through Foraging Behaviour Aderina Dukit, Ito Fuminori, Sze Huei Yek This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8598796/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 Yellow crazy ants ( Anoplolepis gracilipes ) have invaded many areas of conservation concern, including Kinabalu Park, Borneo, Malaysia, where populations occur around substation in the lowland areas. Assessing invasion intensity in protected areas is essential for timely management, yet reliable behavioural indicators remain poorly explored. In this study, we examined the foraging behaviour of A. gracilipes to assess invasion intensity at the Sayap substation in Kinabalu Park using a gel-baiting approach. Infested areas were identified, and active foraging periods were surveyed prior to deploying empty gel baits (without insecticide) measuring approximately 1 cm in width. Baits were monitored at 1-hr intervals to record ant species occupancy and bait monopolisation. Anoplolepis gracilipes workers monopolised only 16.7% of bait stations (3 out of 18), although queens were observed foraging at baits. Most bait stations were visited by six non-target ant species (two Nylanderia species, Cardiocondyla sp., Pheidole comata , Myrmicaria sp., Tetramorium sp.), indicating continued access to resources by native ants. These behavioural patterns suggest that A. gracilipes has not yet reached an invasion intensity sufficient to exclude native ant species at the study site. This study demonstrates that foraging behaviour and bait monopolisation can serve as practical behavioural indicators of invasion intensity in protected tropical environments, supporting early detection and informing timely management of invasive species. invasive ants’ control Kinabalu Park polygynous queen foraging interspecific competitions non-target ants behavioural indicators Figures Figure 1 Figure 2 INTRODUCTION The yellow crazy ant, Anoplolepis gracilipes (Fr.Smith), is one of the world’s 100 worst invasive alien species (Luque et al. 2014 ). The species is widely distributed and has dispersed globally via mostly human-mediated pathways. A. gracilipes poses a significant threat to biodiversity and the abundance of native species in introduced areas (reviewed in Lee and Yang 2022 ). Besides being a direct threat to biodiversity and the abundance of native species, A. gracilipes indirectly affects tree health by feeding on the honeydew of sap-sucking hemipterans. Anoplolepis gracilipes protected these hemipterans, and consequently, this led to a population explosion of tree-damaging sap-sucking hemipterans (Hill et al. 2003 ). Additionally, the presence of A. gracilipes on trees deters pollinators, thereby reducing pollinator visitation rates to flowers (Costa et al. 2023 ). Although A. gracilipes mostly invades anthropogenically disturbed habitats and urban areas (Lee and Yang 2022 ), it can also invade undisturbed forests (Rajesh et al. 2022 ). For example, A. gracilipes populations thrive in tropical island forest fragments (Rajesh et al. 2022 ; Yek et al. 2023 ). In protected forests, they negatively impact native ant diversity (Brühl and Eltz 2010 ) and change the area’s native ant community composition (Ward and Beggs 2007 ). In protected areas of Taiwan, several land crab species are declining in population due to the invasion of A. gracilipes (Lee et al. 2021 ). The dominance of yellow crazy ants in protected areas can be controlled by mixing insecticides in baits (Stewart et al. 2014 ). The key consideration in controlling A. gracilipes in protected areas is selecting a treatment that minimises impacts on non-target ant species (Hoffmann et al. 2016 ). Effective treatment would require A. gracilipes foragers to monopolise these baits and spread the insecticide via trophallaxis to nestmates. Because of its numerical advantage over other ant species, A. gracilipes foragers were often able to monopolise the baits. However, in areas with high native ant diversity, A. gracilipes monopolising baits is not guaranteed. The attractant of these baits is generally attractive to sugar-seeking ants. In a household setting, the non-specificity of the attractant would be monopolised by household pest ants; therefore, a non-specific ant attractant is sufficient. However, in protected areas, many native ant species also engage in trophobioses with hemipterans (Blüthgen et al. 2006 ). Hence, the deployment of baited control methods in protected areas should first assess whether targeted ants monopolise empty gel baits before deploying toxic gel baits for control. This study aims to assess the behavioural dominance of A. gracilipes found in Kinabalu Park. At the study site, we first locate the foraging areas of A. gracilipes . Next, we survey the hours during which A. gracilipes forages actively. Finally, we deploy empty gel bait (bait without insecticides) along the A. gracilipes foraging arena and monitor the ant species that take the bait. If non-target ant species can monopolise the bait, we assess the behavioural interactions of these ants on the baits to predict A. gracilipes invasion intensity at the study site. METHODOLOGY The presence of A. gracilipes was located at a store building of Sayap Substation, Kinabalu Park, Sabah (N6°9’50.42”, E116°33’56.51”; 940 m a.s.l). This building, located near the Kemantis River, is currently used to store domestic supplies for campground use (Fig. 1 A). Once the targeted ants were located, we conducted surveys to assess the foraging activity of A. gracilipes . At this substation, A. gracilipes were active exclusively around the store building, specifically along the cement corridor outside the structure, and foraging activity was observed throughout the day (08:30 h to 19:30 h). Empty gel baits, i.e. without the active ingredient Boric Acid (Trident Ant Gel Bait; provided by SCS Science Sdn. Bhd.), were deployed along the edge of the cement corridor at 1 m intervals. A total of 18 bait drops were placed in a linear arrangement and individually numbered for tracking purposes (Fig. 1 B). Each bait drop measured approximately 1 cm in width. We conducted bait observations from 08:30 h to 19:30 h over 1.5 days. Experiments were stopped when the rain washed the baits off. Baits were monitored at 30-minute to 1-hour intervals (depending on the weather conditions), resulting in 19 observations per bait. Ant species visiting baits were photographed using an Olympus TG-7 camera. The experiment was carried out from 20th to 22nd September, 2025. Representative specimens attracted to the baits were collected, and the specimens were identified to genus level under a binocular microscope. Species identification was possible only for Pheidole using Eguchi’s ( 2001 ) key. Then, ants attracted to the baits were identified from photographs (Supplementary Table 1). We assess bait control suitability based on A. gracilipes monopolising bait stations and excluding all non-target ant species. RESULTS & DISCUSSIONS Ants visited all 18 gel baits during the observation periods. However, only three bait stations (#4, #11, and #17) were continuously monopolised by A. gracilipes (Fig. 2 A). Six other ant species (two species of Nylanderia , Cardiocondyla sp., Pheidole comata , Myrmicaria sp., Tetramorium sp.) also visited the bait stations (Supplementary Table 1). At one bait station (#10), A. gracilipes queen was observed feeding on bait directly, escorted by foragers (Fig. 2 D). Queen walking outside the nests (either foraging or moving) behavior was typical for species with polygynous (multiple queens) and polydomous (i.e., ‘workers and brood of its constituent nests function as a social and cooperative unit and are regularly interchanged among nests’; Debout et al. 2007 ). For example, the successful spread and replacement of native ants by Linepithema humile (Argentine ant) in central Europe have been associated with interchange of workers, broods, and resources among the constituent nests (Holway and Case 2000 ). Nylanderia sp. 1 and Myrmicaria sp. overtake bait stations (#2, #3, #5, #6, #7, #8, #9) already monopolised by A. gracilipes (Fig. 2 B). At bait station #1, Myrmicaria sp. exclude A. gracilipes completely during the observation period, suggesting that Myrmicaria sp. and Nylanderia sp. 1 are engaged in direct competition with A. gracilipes . Myrmicaria sp. in Southeast Asia are frequently observed associated with scale insects and are more common at higher elevations (Yahya et al. 2009 ). These two attributes indicate that at 940 m a.s.l., they could be competitively superior to A. gracilipes . This is consistent with observations at bait station #1, where Myrmicaria sp. arrived before A. gracilipes and monopolised the bait throughout the observational period. Nylanderia sp. 1 is a common pest ant that occurs in the region (Na and Lee 2001 ), with foraging behaviour and feeding niche similar to those of A. gracilipes (Wong et al. 2025 ). Hence, it is unsurprising that they were observed competing for the same resources as A. gracilipes . However, on all occasions, A. gracilipes discovered the bait stations before Nylanderia sp. 1, indicating that they could be outcompeted if A. gracilipes populations outnumbered Nylanderia sp. 1 at the same locality. The remaining four species ( Pheiodole comata , Tetramorium sp., Cardiocondyla sp., and Nylanderia sp. 2) share baits with A. gracilipes (#10, #12, #13, #14, #15, #16, and #18), albeit only marginally (Fig. 2 C). The four ant species are sugar-seeking ant genera and are common pest ants (Na and Lee 2001 ). Their occasional occurrence at the bait stations indicates two non-exclusive possibilities. Firstly, A. gracilipes populations have not yet reached numerical dominance at this location, leaving empty niches for competitively inferior ant species. Second, disturbance at the forest edge (e.g., construction of tourist facilities) reshuffles the ant community (Yek et al. 2023 ), thereby allowing multiple sugar-seeking ants to form a new coexistence network (Grey et al. 2018). These species are expected to be at risk of exclusion from the ant community if A. gracilipes increases in population sizes or forms supercolonies (Drescher et al. 2011 ). Our results indicate that A. gracilipes has the potential to pose a serious threat to native ant communities and biodiversity at the lowland protected forests. The attractants in gel baits are effective at attracting A. gracilipes . However, it is also attractive to other sugar-seeking non-target ants. Until A. gracilipes monopolises all bait stations, control measures are not necessary. This study demonstrates that native ants- A. gracilipes interactions at bait stations can serve as practical behavioural indicators for early detection of invasion severity in Kinabalu Park. Declarations Competing Interests The authors have no relevant financial or non-financial interests to disclose. Author Contribution Aderina Dukit and Sze Huei Yek conceived and designed the research. Aderina Dukit and Fuminori Ito conducted the experiments. Fuminori Ito contributed to ants' identification. Sze Huei Yek analyzed data. The first draft of the manuscript was written by Sze Huei Yek and Aderina Dukit, and all authors commented on previous version of the manuscript. All authors read and approved the final manuscript. Acknowledgement We thank SCS Science Sdn. Bhd. for their generous supplies of the empty gel baits for testing. The project was carried out under permits from the Sabah Biodiversity Council (permit number: JKM/MBS.1000-2/2/1 JLD.1(26)) and Sabah Parks (permit number: SPRP-193) issued to Sze Huei Yek. Data Availability The data generated by this study is available in the Supplementary Table 1. References Blüthgen N, Mezger D, Linsenmair KE (2006) Ant-hemipteran trophobioses in a Bornean rainforest–diversity, specificity and monopolisation. Insectes Sociaux 53(2):194–203 https://doi.org/10.1007/s00040-005-0858-1 Brühl CA, Eltz T (2010) Fuelling the biodiversity crisis: species loss of ground-dwelling forest ants in oil palm plantations in Sabah, Malaysia (Borneo). Biodivers Conserv 19(2):519–529 https://doi.org/10.1007/s10531-009-9596-4 Costa A, Heleno R, Freide EF, Dufrene Y, Huckle E, Kaiser-Bunbury CN (2023) Impacts of invasive ants on pollination of native plants are similar in invaded and restored plant communities. Global Ecol Conserv 42:e02413 https://doi.org/10.1016/j.gecco.2023.e02413 Debout G, Schatz B, Elias M, Mckey D (2007) Polydomy in ants: what we know, what we think we know, and what remains to be done. Biol J Linn Soc 90(2):319–348 https://doi.org/10.1111/j.1095-8312.2007.00728.x Drescher J, Feldhaar H, Blüthgen N (2011) Interspecific aggression and resource monopolization of the invasive ant Anoplolepis gracilipes in Malaysian Borneo. Biotropica 43(1):93–99 https://doi.org/10.1111/j.1744-7429.2010.00662.x Eguchi K (2001) A revision of the Bornean species of the ant genus Pheidole (Insecta: Hymenoptera: Formicidae: Myrmicinae). Tropics Monogr Ser 2:1–154 https://doi.org/10.3759/tropics.MonographNo.2_1 Gray RE, Ewers RM, Boyle MJ, Chung AY, Gill RJ (2018) Effect of tropical forest disturbance on the competitive interactions within a diverse ant community. Sci Rep 8(1):5131 https://doi.org/10.1038/s41598-018-23272-y Hill M, Holm K, Vel T, Shah NJ, Matyot P (2003) Impact of the introduced yellow crazy ant Anoplolepis gracilipes on Bird Island, Seychelles. Biodivers Conserv 12(9):1969–1984 https://doi.org/10.1023/A:1024151630204 Hoffmann BD, Luque GM, Bellard C, Holmes ND, Donlan CJ (2016) Improving invasive ant eradication as a conservation tool: a review. Biol Conserv 198:37–49 https://doi.org/10.1016/j.biocon.2016.03.036 Holway DA, Case TJ (2000) Mechanisms of dispersed central-place foraging in polydomous colonies of the Argentine ant. Anim Behav 59(2):433–441 https://doi.org/10.1006/anbe.1999.1329 Lee CC, Chiu MC, Shih CH, Yang CCS, Liu HC, Lin CC (2021) The role of anthropogenic disturbance and invasion of the yellow crazy ant in a recent decline of land crab population. Sci Rep 11(1):12234 https://doi.org/10.1038/s41598-021-91732-z Lee CY, Yang CCS (2022) Biology, ecology, and management of the invasive longlegged ant, Anoplolepis gracilipes . Ann Rev Entomol 67(1):43–63 https://doi.org/10.1146/annurev-ento-033121-102332 Luque GM, Bellard C, Bertelsmeier C, Bonnaud E, Genovesi P, Simberloff D, Courchamp F (2014) The 100th of the world’s worst invasive alien species. Biol Invasions 16(5):981–985 https://doi.org/10.1007/s10530-013-0561-5 Na JP, Lee CY (2001) Identification key to common urban pest ants in Malaysia. Trop Biomed 18(1):1–17 Rajesh TP, Manoj K, Prashanth Ballullaya U et al (2022) Urban tropical forest islets as hotspots of ants in general and invasive ants in particular. Sci Rep 12(1):12003 https://doi.org/10.1038/s41598-022-16243-x Stewart PLCF, Richards G, Bernard A, Wickenden J (2014) The control of yellow crazy ants ( Anoplolepis gracilipes ): an empirical study. Int J Ecol Dev 27:56–67 Ward D, Beggs J (2007) Coexistence, habitat patterns and the assembly of ant communities in the Yasawa islands. Fiji acta Oecol 32(2):215–223 https://doi.org/10.1016/j.actao.2007.05.002 Wong ZH, Tan HL, Yeo DYC, Yek SH (2025) Ant species on a facultative ant-plant ( Macaranga tanarius ) and their possible roles in herbivory protection. Asian Myrmecology 18:e018002 https://doi.org/10.20362/am.018002 Yahya BE, Yamane S, Mohamed M (2009) Morphological and behavioral characters of the two species groups of the ant genus Myrmicaria (Insecta: Hymenoptera: Formicidae: Myrmicinae) from Southeast Asia. Species Divers 14(4):249–265 https://doi.org/10.12782/specdiv.14.249 Yek SH, Pathy TS, Yeo DYC, Gan JYS (2023) The effects of anthropogenic disturbance and seasonality on the ant communities of Lang Tengah Island. PeerJ 11:e16157 https://doi.org/10.7717/peerj.16157 Additional Declarations No competing interests reported. Supplementary Files SayapSupplementaryTable1.xlsx 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. 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13:07:01","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":317782,"visible":true,"origin":"","legend":"\u003cp\u003e(A) \u003cem\u003eA. gracilipes\u003c/em\u003e monopolised bait #4 during the observational period (B) \u003cem\u003eNylanderia \u003c/em\u003esp.1overtook bait previously occupied by \u003cem\u003eA. gracilipes\u003c/em\u003e (C) \u003cem\u003ePheidole comata\u003c/em\u003e (circled red) co-shares the bait with \u003cem\u003eA. gracilipes\u003c/em\u003e (D) \u003cem\u003eA. gracilipes\u003c/em\u003e’s queen feeding on bait #10, surrounded by workers\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8598796/v1/60971445473525fbfc2e5d2a.jpeg"},{"id":101204681,"identity":"cc7a06d0-c576-4e78-b70c-f0c4a6e61de7","added_by":"auto","created_at":"2026-01-27 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\u003cem\u003eAnoplolepis gracilipes\u003c/em\u003e (Fr.Smith), is one of the world\u0026rsquo;s 100 worst invasive alien species (Luque et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The species is widely distributed and has dispersed globally \u003cem\u003evia\u003c/em\u003e mostly human-mediated pathways. \u003cem\u003eA. gracilipes\u003c/em\u003e poses a significant threat to biodiversity and the abundance of native species in introduced areas (reviewed in Lee and Yang \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Besides being a direct threat to biodiversity and the abundance of native species, \u003cem\u003eA. gracilipes\u003c/em\u003e indirectly affects tree health by feeding on the honeydew of sap-sucking hemipterans. \u003cem\u003eAnoplolepis gracilipes\u003c/em\u003e protected these hemipterans, and consequently, this led to a population explosion of tree-damaging sap-sucking hemipterans (Hill et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). Additionally, the presence of \u003cem\u003eA. gracilipes\u003c/em\u003e on trees deters pollinators, thereby reducing pollinator visitation rates to flowers (Costa et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAlthough \u003cem\u003eA. gracilipes\u003c/em\u003e mostly invades anthropogenically disturbed habitats and urban areas (Lee and Yang \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), it can also invade undisturbed forests (Rajesh et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). For example, \u003cem\u003eA. gracilipes\u003c/em\u003e populations thrive in tropical island forest fragments (Rajesh et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Yek et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). In protected forests, they negatively impact native ant diversity (Br\u0026uuml;hl and Eltz \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2010\u003c/span\u003e) and change the area\u0026rsquo;s native ant community composition (Ward and Beggs \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). In protected areas of Taiwan, several land crab species are declining in population due to the invasion of \u003cem\u003eA. gracilipes\u003c/em\u003e (Lee et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe dominance of yellow crazy ants in protected areas can be controlled by mixing insecticides in baits (Stewart et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The key consideration in controlling \u003cem\u003eA. gracilipes\u003c/em\u003e in protected areas is selecting a treatment that minimises impacts on non-target ant species (Hoffmann et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Effective treatment would require \u003cem\u003eA. gracilipes\u003c/em\u003e foragers to monopolise these baits and spread the insecticide \u003cem\u003evia\u003c/em\u003e trophallaxis to nestmates. Because of its numerical advantage over other ant species, \u003cem\u003eA. gracilipes\u003c/em\u003e foragers were often able to monopolise the baits. However, in areas with high native ant diversity, \u003cem\u003eA. gracilipes\u003c/em\u003e monopolising baits is not guaranteed. The attractant of these baits is generally attractive to sugar-seeking ants. In a household setting, the non-specificity of the attractant would be monopolised by household pest ants; therefore, a non-specific ant attractant is sufficient. However, in protected areas, many native ant species also engage in trophobioses with hemipterans (Bl\u0026uuml;thgen et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Hence, the deployment of baited control methods in protected areas should first assess whether targeted ants monopolise empty gel baits before deploying toxic gel baits for control.\u003c/p\u003e \u003cp\u003eThis study aims to assess the behavioural dominance of \u003cem\u003eA. gracilipes\u003c/em\u003e found in Kinabalu Park. At the study site, we first locate the foraging areas of \u003cem\u003eA. gracilipes\u003c/em\u003e. Next, we survey the hours during which \u003cem\u003eA. gracilipes\u003c/em\u003e forages actively. Finally, we deploy empty gel bait (bait without insecticides) along the \u003cem\u003eA. gracilipes\u003c/em\u003e foraging arena and monitor the ant species that take the bait. If non-target ant species can monopolise the bait, we assess the behavioural interactions of these ants on the baits to predict \u003cem\u003eA. gracilipes\u003c/em\u003e invasion intensity at the study site.\u003c/p\u003e"},{"header":"METHODOLOGY","content":"\u003cp\u003eThe presence of \u003cem\u003eA. gracilipes\u003c/em\u003e was located at a store building of Sayap Substation, Kinabalu Park, Sabah (N6°9’50.42”, E116°33’56.51”; 940 m a.s.l). This building, located near the Kemantis River, is currently used to store domestic supplies for campground use (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA). Once the targeted ants were located, we conducted surveys to assess the foraging activity of \u003cem\u003eA. gracilipes\u003c/em\u003e. At this substation, \u003cem\u003eA. gracilipes\u003c/em\u003e were active exclusively around the store building, specifically along the cement corridor outside the structure, and foraging activity was observed throughout the day (08:30 h to 19:30 h). Empty gel baits, \u003cem\u003ei.e.\u003c/em\u003e without the active ingredient Boric Acid (Trident Ant Gel Bait; provided by SCS Science Sdn. Bhd.), were deployed along the edge of the cement corridor at 1 m intervals. A total of 18 bait drops were placed in a linear arrangement and individually numbered for tracking purposes (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB). Each bait drop measured approximately 1 cm in width. We conducted bait observations from 08:30 h to 19:30 h over 1.5 days. Experiments were stopped when the rain washed the baits off. Baits were monitored at 30-minute to 1-hour intervals (depending on the weather conditions), resulting in 19 observations per bait. Ant species visiting baits were photographed using an Olympus TG-7 camera. The experiment was carried out from 20th to 22nd September, 2025. Representative specimens attracted to the baits were collected, and the specimens were identified to genus level under a binocular microscope. Species identification was possible only for \u003cem\u003ePheidole\u003c/em\u003e using Eguchi’s (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2001\u003c/span\u003e) key. Then, ants attracted to the baits were identified from photographs (Supplementary Table\u0026nbsp;1). We assess bait control suitability based on \u003cem\u003eA. gracilipes\u003c/em\u003e monopolising bait stations and excluding all non-target ant species.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e "},{"header":"RESULTS \u0026 DISCUSSIONS","content":"\u003cp\u003eAnts visited all 18 gel baits during the observation periods. However, only three bait stations (#4, #11, and #17) were continuously monopolised by \u003cem\u003eA. gracilipes\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). Six other ant species (two species of \u003cem\u003eNylanderia\u003c/em\u003e, \u003cem\u003eCardiocondyla\u003c/em\u003e sp., \u003cem\u003ePheidole comata\u003c/em\u003e, \u003cem\u003eMyrmicaria\u003c/em\u003e sp., \u003cem\u003eTetramorium\u003c/em\u003e sp.) also visited the bait stations (Supplementary Table\u0026nbsp;1). At one bait station (#10), \u003cem\u003eA. gracilipes\u003c/em\u003e queen was observed feeding on bait directly, escorted by foragers (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD). Queen walking outside the nests (either foraging or moving) behavior was typical for species with polygynous (multiple queens) and polydomous (i.e., ‘workers and brood of its constituent nests function as a social and cooperative unit and are regularly interchanged among nests’; Debout et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). For example, the successful spread and replacement of native ants by \u003cem\u003eLinepithema humile\u003c/em\u003e (Argentine ant) in central Europe have been associated with interchange of workers, broods, and resources among the constituent nests (Holway and Case \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2000\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e \u003cem\u003eNylanderia\u003c/em\u003e sp. 1 and \u003cem\u003eMyrmicaria\u003c/em\u003e sp. overtake bait stations (#2, #3, #5, #6, #7, #8, #9) already monopolised by \u003cem\u003eA. gracilipes\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB). At bait station #1, \u003cem\u003eMyrmicaria\u003c/em\u003e sp. exclude \u003cem\u003eA. gracilipes\u003c/em\u003e completely during the observation period, suggesting that \u003cem\u003eMyrmicaria\u003c/em\u003e sp. and \u003cem\u003eNylanderia\u003c/em\u003e sp. 1 are engaged in direct competition with \u003cem\u003eA. gracilipes\u003c/em\u003e. \u003cem\u003eMyrmicaria\u003c/em\u003e sp. in Southeast Asia are frequently observed associated with scale insects and are more common at higher elevations (Yahya et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). These two attributes indicate that at 940 m a.s.l., they could be competitively superior to \u003cem\u003eA. gracilipes\u003c/em\u003e. This is consistent with observations at bait station #1, where \u003cem\u003eMyrmicaria\u003c/em\u003e sp. arrived before \u003cem\u003eA. gracilipes\u003c/em\u003e and monopolised the bait throughout the observational period. \u003cem\u003eNylanderia\u003c/em\u003e sp. 1 is a common pest ant that occurs in the region (Na and Lee \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2001\u003c/span\u003e), with foraging behaviour and feeding niche similar to those of \u003cem\u003eA. gracilipes\u003c/em\u003e (Wong et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Hence, it is unsurprising that they were observed competing for the same resources as \u003cem\u003eA. gracilipes\u003c/em\u003e. However, on all occasions, \u003cem\u003eA. gracilipes\u003c/em\u003e discovered the bait stations before \u003cem\u003eNylanderia\u003c/em\u003e sp. 1, indicating that they could be outcompeted if \u003cem\u003eA. gracilipes\u003c/em\u003e populations outnumbered \u003cem\u003eNylanderia\u003c/em\u003e sp. 1 at the same locality.\u003c/p\u003e\u003cp\u003eThe remaining four species (\u003cem\u003ePheiodole comata\u003c/em\u003e, \u003cem\u003eTetramorium\u003c/em\u003e sp., \u003cem\u003eCardiocondyla\u003c/em\u003e sp., and \u003cem\u003eNylanderia\u003c/em\u003e sp. 2) share baits with \u003cem\u003eA. gracilipes\u003c/em\u003e (#10, #12, #13, #14, #15, #16, and #18), albeit only marginally (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC). The four ant species are sugar-seeking ant genera and are common pest ants (Na and Lee \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). Their occasional occurrence at the bait stations indicates two non-exclusive possibilities. Firstly, \u003cem\u003eA. gracilipes\u003c/em\u003e populations have not yet reached numerical dominance at this location, leaving empty niches for competitively inferior ant species. Second, disturbance at the forest edge (e.g., construction of tourist facilities) reshuffles the ant community (Yek et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), thereby allowing multiple sugar-seeking ants to form a new coexistence network (Grey et al. 2018). These species are expected to be at risk of exclusion from the ant community if \u003cem\u003eA. gracilipes\u003c/em\u003e increases in population sizes or forms supercolonies (Drescher et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eOur results indicate that \u003cem\u003eA. gracilipes\u003c/em\u003e has the potential to pose a serious threat to native ant communities and biodiversity at the lowland protected forests. The attractants in gel baits are effective at attracting \u003cem\u003eA. gracilipes\u003c/em\u003e. However, it is also attractive to other sugar-seeking non-target ants. Until \u003cem\u003eA. gracilipes\u003c/em\u003e monopolises all bait stations, control measures are not necessary. This study demonstrates that native ants-\u003cem\u003eA. gracilipes\u003c/em\u003e interactions at bait stations can serve as practical behavioural indicators for early detection of invasion severity in Kinabalu Park.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eCompeting Interests\u003c/h2\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\n\u003cp\u003eAderina Dukit and Sze Huei Yek conceived and designed the research. Aderina Dukit and Fuminori Ito conducted the experiments. Fuminori Ito contributed to ants' identification. Sze Huei Yek analyzed data. The first draft of the manuscript was written by Sze Huei Yek and Aderina Dukit, and all authors commented on previous version of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003ch2\u003eAcknowledgement\u003c/h2\u003e\n\u003cp\u003eWe thank SCS Science Sdn. Bhd. for their generous supplies of the empty gel baits for testing. The project was carried out under permits from the Sabah Biodiversity Council (permit number: JKM/MBS.1000-2/2/1 JLD.1(26)) and Sabah Parks (permit number: SPRP-193) issued to Sze Huei Yek.\u003c/p\u003e\n\u003ch2\u003eData Availability\u003c/h2\u003e\n\u003cp\u003eThe data generated by this study is available in the Supplementary Table 1.\u003c/p\u003e\n\u003ch3\u003e\u0026nbsp;\u003c/h3\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBl\u0026uuml;thgen N, Mezger D, Linsenmair KE (2006) Ant-hemipteran trophobioses in a Bornean rainforest\u0026ndash;diversity, specificity and monopolisation. 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PeerJ 11:e16157\u0026nbsp;\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.7717/peerj.16157\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"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":"invasive ants’ control, Kinabalu Park, polygynous queen foraging, interspecific competitions, non-target ants, behavioural indicators","lastPublishedDoi":"10.21203/rs.3.rs-8598796/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8598796/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eYellow crazy ants (\u003cem\u003eAnoplolepis gracilipes\u003c/em\u003e) have invaded many areas of conservation concern, including Kinabalu Park, Borneo, Malaysia, where populations occur around substation in the lowland areas. Assessing invasion intensity in protected areas is essential for timely management, yet reliable behavioural indicators remain poorly explored. In this study, we examined the foraging behaviour of \u003cem\u003eA. gracilipes\u003c/em\u003e to assess invasion intensity at the Sayap substation in Kinabalu Park using a gel-baiting approach. Infested areas were identified, and active foraging periods were surveyed prior to deploying empty gel baits (without insecticide) measuring approximately 1 cm in width. Baits were monitored at 1-hr intervals to record ant species occupancy and bait monopolisation. \u003cem\u003eAnoplolepis gracilipes\u003c/em\u003e workers monopolised only 16.7% of bait stations (3 out of 18), although queens were observed foraging at baits. Most bait stations were visited by six non-target ant species (two \u003cem\u003eNylanderia\u003c/em\u003e species, \u003cem\u003eCardiocondyla\u003c/em\u003e sp., \u003cem\u003ePheidole comata\u003c/em\u003e, \u003cem\u003eMyrmicaria\u003c/em\u003e sp., \u003cem\u003eTetramorium\u003c/em\u003e sp.), indicating continued access to resources by native ants. These behavioural patterns suggest that \u003cem\u003eA. gracilipes\u003c/em\u003e has not yet reached an invasion intensity sufficient to exclude native ant species at the study site. This study demonstrates that foraging behaviour and bait monopolisation can serve as practical behavioural indicators of invasion intensity in protected tropical environments, supporting early detection and informing timely management of invasive species.\u003c/p\u003e","manuscriptTitle":"Assessing Invasion Intensity of the Yellow Crazy Ant (Anoplolepis gracilipes) Through Foraging Behaviour","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-01-16 11:07:30","doi":"10.21203/rs.3.rs-8598796/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":"53aa3206-a968-44b8-bd8e-ab7802d5c2bf","owner":[],"postedDate":"January 16th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-01-24T18:24:06+00:00","versionOfRecord":[],"versionCreatedAt":"2026-01-16 11:07:30","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8598796","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8598796","identity":"rs-8598796","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}