Parasitoids deter foraging by Argentine ants (Linepithema humile) in theirnative habitat in Brazil

The Argentine ant, Linepithema humile, has invaded sites across Africa, Aus tralia, Europe, and North America. In its introduced ranges it eliminates n ative ants and tends agricultural pests. Few studies have examined the ecol ogy of Argentine ants in their native habitat. This study examined the effe cts of parasitoid flies. genus Pseudacteon, on the foraging behavior of Arg entine ants in part of their native range in southern Brazil. Pseudacteon p arasitoids commonly attacked Argentine ants, but not other ant species, in daylight at temperatures above 18 degrees C, Argentine ants abandoned food resources and returned underground in the presence of parasitoids. Parasito id attack rates diminished as Argentine ants retreated underground. Where p arasitoids were present, Argentine ants were abundant at food resources onl y during times of day when parasitoids were inactive. Where parasitoids wer e absent. Argentine ants were abundant at food resources throughout the day . Overall, the presence of parasitoids explained observed variation in Arge ntine ant foraging far better than temperature, although temperature had so me effect. The results suggest that Pseudacteon parasitoids inhibit the abi lity of Argentine ants to gather food resources in their native habitat in Brazil.