FORAGING ECOLOGY AND PATTERNS OF DIVERSIFICATION IN DIPTERAN PARASITOIDS OF FIRE ANTS IN SOUTH BRAZIL

1. At least sixteen species of parasitoid flies in the genus Pseudacte on (family Phoridae) attack fire ants in the Solenopsis saevissima sub complex in South America. Little is known of behavioural or ecological differences among Pseudacteon parasitoids of fire ants, although thei r coexistence in multispecies communities would suggest that important differences exist. Seven Pseudacteon species in two separate communit ies were studied in south-east Brazil. The way in which hosts detect a nd respond to the presence of parasitoids, attack rates of the parasit oids, and host location behaviour of the parasitoids were examined. 2. Reductions in fire ant recruitment were more closely related to the n umber of ants attacked along a foraging trail than to the amount of ti me that a phorid was present. 3. Pseudacteon solenopsidis differed fro m other phorid species by flying backwards while pursuing ants, by att acking at lower rates than other phorids, and by spending longer aroun d fire ant foraging trails than other phorids before departing. Fire a nt recruitment to food often rebounded in the continued presence of P. solenopsidis. 4. In each of the two communities, certain Pseudacteon species appeared frequently at Solenopsis foraging trails, whereas oth ers appeared predominantly at mound disturbances. Two distinct size cl asses of phorids were present in each community, and the community wit h the larger ant host species also had a third and larger phorid speci es. No phorid species from the same community had similar body sizes a nd similar host location behaviours, although numerous species from di fferent communities shared both of these traits. 5. Heterogeneity in h ost size and in the ecological circumstances under which hosts are vul nerable to attack appears to have influenced the evolution and perhaps maintenance of diverse Pseudacteon communities.