Effect of broadcast bait application on non-target invasive and native ants in natural and urban areas

We applied Amdro (0.73% hydramethylnon), an ant-specific bait, to large natural (four years) and urban areas (three years) to suppress the invasive red imported fire ant. Non-target species were monitored to determine if there were deleterious affects. At a pine-mixed hardwood site, odorous house ant, Tapinoma sessile (Say) and the invasive rover ant, Brachymyrmex patagonicus, displayed a positive response to treatment; their numbers increased in trap catches. Little black ant, Monomorium minimum and Paratrechina faisonensis (Forel) did not respond to treatment and appear to coexist with RIFA in this ecosystem. At the longleaf-pine dominated site, we found little black ant and Prenolepis imparis (Say) exhibited negative response to treatments; their numbers decreased in traps after treatment. In study at another pine-mixed hardwood ecosystem, Myrmecine ants, with the exception of Solenopsis spp. and Pheidole spp., were almost eliminated by treatment. Aphaenogaster fulva-rudis-texana was the most notable example. In urban areas, the affect of Amdro was most noticeable on invasive species such as Brachymyrmex patagonicus, Tetramorium sp. and Linepithema humile which all increased after treatment. Most native species were not affected or slightly suppressed initially but were found in similar numbers to the untreated control in subsequent months. Large scale use of ant-specific bait such as Amdro has been advocated in recent years due to its successful, long-term suppression of fire ants in urban areas. Ecosystem managers have considered this approach as a way to suppress fire ants, restore balance to the ecosystem, and protect diminishing numbers of ground-dwelling vertebrates such as mice and birds. Long-term suppression fire ant suppression was not seen in complex ecosystems such as long-leaf pine savannahs and pine-mixed hardwood areas. The non-target affects of Amdro on potential fire ant competitors and natural enemy ants warrant caution in applying broadcast baits on a large scale in natural ecosystems.