Efficacy, non-target impacts, and other considerations of unregistered fipronil-laced baits being used in multiple invasive ant eradication programs

We present three studies assessing the efficacy and non-target impacts of multiple unregistered forms of hydrogel ant baits, as well as some co-use with the granular bait Antoff, that were experimentally used targeting Argentine ant, Linepithema humile, and yellow crazy ant, Anoplolepis gracilipes, within natural/semi-natural environments in Australia. The three studies varied greatly in design and treatment regimens, and were each conducted to address real-time learning needs while attempting to understand how best to use these experimental baits within the spatial, temporal and logistic limitations of three eradication programs. All studies involved broadscale applications of numerous forms of the baits, with greatly varying treatment regimens, coupled with before-after sampling of ant communities, as well as other soil invertebrates in one study. All studies found the baits were highly efficacious against both species, more so for A. gracilipes than L. humile . Eradication is considered to have been achieved for A. gracilipes in one treatment area with a triple treatment regimen, but not using different treatment regimens in other areas. Six treatments conducted approximately one week apart did not eradicate L. humile . Few non-target impacts were found, predominantly occurring only when sampling was conducted within days of a treatment, or at the end of six treatments of a high application rate. Instead, non-target species richness and composition were most often more affected by spatial location or sample time than treatment. Any treatment effects were non-persistent after 6–18 months. Hydrogel baits are likely to have significant roles to play for ant management and eradication.