5. Conclusion Table 1 Treatment protocols for management of Wasmannia auropunctata in Taiwan. Type of Treatment Ground treatment Bait formulations used Commercial granular bait containing 0.73% hydramethylnon & commercial granular bait containing 0.50% pyriproxyfen Arboreal treatment Laboratory formulated paste bait containing 10% sucrose, 2% borax, and 0.5% carboxymethyl cellulose C.C. LEE et al. dehydration and starvation. The little fire ant, Wasmannia auropunctata, a notorious stinging species was first reported in East Asia in 2021, in two populations in Taiwan that were found that were genetically similar, forming a unicolonial social structure. Because of this ant’s highly aggressive nature, its painful sting and potential for agricultural impacts, a joint university-government effort was launched to survey the ant and find ways of controlling it. The ant was found to have a semi-arboreal nature, requiring a multi-pronged “combination-treatment” a approach. We approach using three different bait formulations: two types of granular baits (hydramethylnon-based and pyriproxyfen-based) for the ground layer, and a paste bait containing borax for the arboreal layer (Table 1). Acknowledgement This study was funded by the Animal and Plant Health Inspection Agency, Ministry of Agriculture, R.O.C. We greatly appreciate Yu-Pang Chan for producing the location map shown in this paper. We would also like to extend our gratitude to Masako Ogasawara (Okinawa Institute of Science and Technology Graduate University) and Yu-Chun Hsiao (National Chung Hsing University) for providing some of the photos used in this paper. References How to apply Pyriproxyfen granules is mixed with hydramethylnon granules at a ratio of 4: 1, and then deployed on the ground Apply using handheld powder spreader at an application rate of 2.5 kg/ha, with a one-month interval between treatments Paste borax bait is sprayed on tree trunks and vegetation Apply using knapsack sprayer at an application rate of 10L/ha, with a one-month interval between treatments Abedrabbo, S. (1994) Control of the little fire ant, Wasmannia auropunctata, on Santa Fe Island in the Galapagos Islands. In: Williams, D.F. (ed.), Exotic Ants : Biology, Impact, and Control of Introduced Species, 219–227, CRC Press, Boulder. Banks, W.A., Miles, L.R. and Harlan, D.P. (1983) The effects of insect growth regulators and their potential as control agents for imported fire ants (Hymenoptera: Formicidae). The Florida Entomologist, 66: 172–181. Bao, S.Z, Kafle, L. and Shih, C.J. (2011) A new baited trap for monitoring Solenopsis invicta (Formicidae: Hymenoptera) in Taiwan. Applied Entomology and Zoology, 46: 165–169. Cabral, S.K., Hara, A.H. and Niino-DuPonte, R. (2017) Response of little fire Ant (Hymenoptera: Formicidae) colonies to insect growth regulators and hydramethylnon. Proceedings of the Hawaiian Entomological Society, 49: 1–10. terms of both in colonies, mortality In Taiwan, apart from treatment of the ground layer using two types of granular baits, a laboratory formulated paste bait matrix (Social Insect Laboratory, NCUE, 2021) sucrose, 2% borax, and 0.5% containing 10% carboxymethyl cellulose (added as pasting agent) (hereafter referred as paste borax bait) has also been applied to tree trunks and vegetation in the infested areas, since September 2021. The paste borax bait was applied with a knapsack sprayer at an application rate of 10 L/ha (Fig. 7b). Similar to the ground treatment, the paste borax bait was applied monthly. Previous studies in regions where these ants have been introduced (e.g., Hawaii) have found that arboreal W. auropunctata nests in tree canopies and may forage exclusively in the arboreal layer without foraging on the ground. This compromises their chances of encountering granular baits and subsequently affects the success rate of treatment (Montgomery et al., 2015; Souza et al., 2008). Similarly, in Wuri and Heping Districts, it is common to see W. auropunctata nesting in tree trunks (e.g. underneath living tree bark) or observe active ant foraging trails on trees. Unlike granular formulations, paste formulations can adhere to tree trunks and other vertical surfaces (Vanderwoude et al., 2010). Therefore, arboreal treatment using paste borax bait complements the use of granular baits by giving arboreal populations of W. auropunctata access to the insecticidal bait. Boron compounds, such as borax, are known to weaken the exoskeleton and alter the midgut structure of insects (Ebeling et al., 1975; Habes et al., 2006, Wang & Bennett, 2010). Thus, individuals of W. auropunctata that have ingested a lethal amount of borax die from adopted 156 ultimately leading to substantial colony mortality due to the lack of replacement ants (Banks et al., 1983; Reimer in et al., 1991; Tay & Lee, 2014). Therefore, pyriproxyfen-treated of W. auropunctata colony members occurs more gradually, and a significant drop in worker numbers or colony death can only be achieved after two to three months (Cabral et al., 2017). It is worth noting that we chose pyriproxyfen granular bait over other IGR baits, such as methoprene granular bait, since previous studies have shown that its pyriproxyfen performs better consistency in disrupting the production of replacement workers and its attractiveness (Cabral et al., 2017; Hara et al., 2014).
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