Host specificity of Pseudacteon (Diptera : Phoridae) parasitoids that attack Linepithema (Hymenoptera : Formicidae) in South America

The Argentine ant, Linepithema humile (Mayr), is native to South America an d invasive in many, parts of the world, including North America. Various mo rphological forms of L. humile exist in South America, and it is possible t hat some forms may, comprise distinct species. In Brazil, L. humile is repo rted to be attacked by, parasitoids in the genus Pseudacteon (Diptera: Phor idae). if Pseudacteon parasitoids attack, the invasive form of L, humile, t hey may be candidates for biological control of this ant. We compared body, size, scape length, in id pro notal pilosity among populations of L. humil e that were attacked by parasitoids and those that lacked parasitoids. Ants that hosted parasitoids at foraging trails in Brazil tended to have more p ronotal hairs and shorter scapes than ants that did not host parasitoids in Brazil, Argentina, and North America. We used paired experimental trials t o determine whether phorid parasitoids exhibit narrow host specificity or w hether they, will attack the invasive form of L humile if given the opportu nity, Parasitoids located their natural host form but did not locate either North American L. humile or morphologically, similar ants from Brazil. Tog ether these results suggest that various forms previously treated its L. hu mile, are in fact separate species, that L. humile is not a natural host of the parasitoids studied here, and that these parasitoids are not candidate s for biological control of Argentine ants in North America.