Distribution, abundance and persistence of species of Orasema (Hym: Eucharitidae) parasitic on fire ants in South America

Parasitoid wasps of the genus Orasema Cameron have been considered as potential candidates for biological control of imported fire ants in the United States. Surveys were conducted for their occurrence in fire ant colonies across southern South America. In Argentina, 443 ant colonies were excavated at 57 sites and 11 positive sites were revisited to monitor the field persistence. In Paraguay, Bolivia and Uruguay, 288 colonies were examined in the field in 16 sites. Orasema simplex Heraty was the most abundant species, and found in 63.7% of the total parasitized colonies (n = 72). Orasema xanthopus (Cameron) and Orasema salebrosa Heraty were found at four sites in Argentina. In Bolivia, Orasema pireta Heraty was found at one site and parasitizing an unidentified Solenopsis species. Two new host species for Orasema were discovered, Solenopsis quinquecuspis Forel and Solenopsis macdonaghi Santschi. In addition, Orasema aenea Gahan was found parasitizing fire ants for the first time. The parasitoids persisted at 36.4% of the positive sites, most of them in rural habitats.