LAUSR

Pesticides are frequently used to eradicate invasive ant species, but pose ecological harm. Previous studies assessed non-target effects only in terms of the increase or decrease of abundance or species richness after pesticide applications. Positive effects of the release from pressure caused by invasive ant species have not been considered so far. To more accurately assess pesticide effects in the field, the non-target effects of pesticides should be considered separately from the positive effects of such releases. Here, we used monitoring data of ants and other invertebrates collected in a program for the eradication of the Argentine ant, Linepithema humile (Mayr), using fipronil. First, we separately assessed the effects of L. humile abundance and fipronil exposure on non-target ants and other invertebrates using generalized linear models. The abundance of L. humile and the number of pesticide treatments were negatively associated with the total number of non-target individuals and taxonomic richness. We also noted negative relationships between the number of individuals of some ant species and other invertebrate taxonomic groups. The L. humile × pesticide interaction was significant, suggesting that the abundance of L. humile affected the level of impact of pesticide treatment on non-target fauna. Second, we evaluated the dynamics of non-target ant communities for 3 years using principal response curve analyses. Non-target ant communities treated with fipronil continuously for 3 years recovered little, whereas those treated for 1 year recovered to the level of the untreated and non-invaded environment.