Impacts of red imported fire ants (Solenopsis invicta Buren) on native faunal communities in two pine-dominated forests

Abstract

Impacts red imported fire ants (RIFA) exert on native faunal communities were monitored in two pine-dominated ecosystems in Louisiana. After suppression of established RIFA populations with Amdro®, cotton mice (Peromyscus gossypinus), herpetofaunal, ground-dwelling invertebrate, Lycosidae, and non-target ant communities were compared between untreated-control and treated plots with respect to possible ecological impacts of RIFA on these communities. Efficacy of Amdro® (A. I. 0.7% hydramethylnon) was tested at Alexander State Forest and Sandy Hollow WMA, and was found to be effective at both sites for 99-42.3% and 97-48%, respectively, suppression of RIFA on treated plots, for three to seven months, with treatments administered in the evening at a rate 1.68 kg/ha. Following suppression, RIFA were shown to minimally impact cotton mice, ground-dwelling invertebrate populations, and Lycosidae species, indicating that RIFA is not the regulating factor in these communities. In the case of cotton mice, habitat conditions that favor cotton mice may also favor RIFA. The majority of non-target ants analyzed at Alexander State Forest and Sandy Hollow WMA also seem to coexist with RIFA, although some species including Aphaenogaster rudis-texana, Crematogaster lineolata, Brachymrymex musculus, Paratrechina faisonensis, Pheidole dentata, and Pheidole metallescens may occur in sparse, small populations in the presence of RIFA. At Alexander State Forest, both Brachymrymex musculus and Tapinoma sessile showed a positive response to RIFA suppression, indicating signs of competitive release. At Sandy Hollow WMA Monomorium minimum and Prenolepis imparis responded negatively to treatment, indicating that Amdro® may exhibit non-target effects to these two species. Herpetofaunal communities, particularly ground skink and southeastern five-lined skink populations may be negatively impacted by RIFA. However sample sizes for all herpetofauna species were low. Amdro® is effective at suppressing RIFA populations in forested ecosystems; however the impacts RIFA pose on native ground-dwelling faunal communities may be minimal in these two pine-dominated communities.