Ecological interactions among ants in the genus Linepithema, their phorid parasitoids, and ant competitors

1. Many ant species abandon foraging and retreat underground when parasitoids in the dipteran family Phoridae are present. Although the influence of phorids on ant foraging is well documented, their influence on interspecific competition is less studied. This study examined whether phorids influenced the competitive ability of host ants in the genus Linepithema at two sites in Brazil. 2. The phorid Pseudacteon lontrae attacked Linepithema piliferum at one site, while the phorid Pseudacteon pusillus attacked an unknown Linepithema (Linepithema sp.) at the other site. Phorid parasitoids of Linepithema were far more common than phorids of other ant species. 3. Despite a high abundance of phorids, it was difficult to conclude that they influenced competition. Captures in pitfall traps indicated that host Linepithema were most active during times of day when phorids were inactive. 4. Camponotus rufipes and Brachymyrmex sp., the most common competitors of Linepithema sp. (60% of all interactions), dominated Linepithema sp. during the day regardless of phorids. Remaining ant species could not be evaluated individually because they interacted with Linepithema sp. infrequently. 5. Ectatomma brunneum was the most common competitor of L. piliferum (58% of all interactions). The high abundance of phorids at this site made it impossible to evaluate interactions between E. brunneum and L. piliferum in the absence of phorids. 6. Phorids seldom influenced exploitative competition by causing host Linepithema to abandon the bait when no ant competitors were present.28220321

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 and invasive in many, parts of the world, including North America. Various morphological forms of L. humile exist in South America, and it is possible that some forms may, comprise distinct species. In Brazil, L. humile is reported to be attacked by, parasitoids in the genus Pseudacteon (Diptera: Phoridae). if Pseudacteon parasitoids attack, the invasive form of L, humile, they may be candidates for biological control of this ant. We compared body, size, scape length, in id pro notal pilosity among populations of L. humile that were attacked by parasitoids and those that lacked parasitoids. Ants that hosted parasitoids at foraging trails in Brazil tended to have more pronotal hairs and shorter scapes than ants that did not host parasitoids in Brazil, Argentina, and North America. We used paired experimental trials to determine whether phorid parasitoids exhibit narrow host specificity or whether they, will attack the invasive form of L humile if given the opportunity, Parasitoids located their natural host form but did not locate either North American L. humile or morphologically, similar ants from Brazil. Together these results suggest that various forms previously treated its L. humile, are in fact separate species, that L. humile is not a natural host of the parasitoids studied here, and that these parasitoids are not candidates for biological control of Argentine ants in North America.30474274