Development of alginate hydrogel baits for the management of longlegged ant (Hymenoptera: Formicidae)

The longlegged ant, Anoplolepis gracilipes, is a globally destructive invasive species owning to its devastating impacts on biodiversity and ecosystem functions in the regions where it has been introduced. In Taiwan, invasion of A. gracilipes has been associated with the declining of land crab populations in several hotspots. While liquid baiting program has been implemented in those areas, the operation is costly and labor-intensive since it typically requires the use and maintenance of bait stations. The goal of the current study was to evaluate the potential and effectiveness of hydrogel baits laced with borax as an alternative tool to control A. gracilipes. Laboratory studies demonstrated that hydrogel baits containing 3% borax achieved higher A. gracilipes mortality than those containing 2% and 1% borax. Specifically, hydrogel baits containing 3% borax resulted in >90% worker mortality within 21 d post-treatment (LT50 = 5.1 d), along with significant reduction in brood weight (>90%) and substantial queen death (>80% of colony fragments). Furthermore, field experiment indicated that A. gracilipes workers preferentially retrieved small-size hydrogel beads (3.1 mm OD; proportion removed = 1.00 ± 0.00) compared to the larger ones (6.2 mm OD; proportion removed = 0.03 ± 0.03), which will facilitate efficient transfer of toxicant within the colony and may minimize nontarget impact. In conclusion, alginate hydrogel baits with 3% borax appear to be a promising tool against A. gracilipes, although their field efficacy against large supercolonial populations remains to be investigated.