Diversity of fire ant decapitating flies in South America

LUIS CALCATERRA, SANFORD PORTER, AND JUAN BRIANO

Davos, Switzerland

Simposio; II International Symposium of biological Control of Arthropods; 2005

Flies in genus Pseudacteon Coquillett (Diptera: Phoridae) are being used as biocontrol agent against imported fire ants (Hymenoptera: Formicidae) in the United States. Three species flies (four biotypes) from Argentina and Brazil have just been released in eight states. However, the distribution and abundance of most of the species in their homeland are poorly known. This work details the occurrence and abundance of Pseudacteon species in southern South America. Around 3,000 flies belonging to 14 species were found at 50% of the fire ant mounds examined at almost 150 collecting sites where at least one fly was found. Flies occurred in a wide variety of habitats and hosts at altitudes from sea level to 2,280 m (fire ant species were found up to 3,064 m). Pseudacteon obtusus Borgmeier was found at the highest altitude and at the most western longitude (69º21´W). Flies were active between 16 and 37ºC, 15 and 90% relative humidity, and 0 and 11.6 km/h wind speed. Pseudacteon curvatus Borgmeier showed the highest abundance and one of the broadest geographical distributions. Pseudacteon tricuspis Borgmeier, P. litoralis Borgmeier, P. obtusus, P. nudicornis Borgmeier, and P. nocens Borgmeier were also widely distributed. These species appear to be the most generalized within saevissima-group. Pseudacteon solenopsidis Schmitz was only collected attacking isolated workers. A new Pseudacteon species was discovered in northwestern Argentina. Seven fly species were reported for the first time on a new fire ant hosts in this region. The presence of S. invicta was also confirmed in this region. It is the most western occurrence (23º42´S, 64º52´W) and the highest altitude is reported for S. invicta in its native land. Pseudacteon cultellatus Borgmeier was found for the first time on S. invicta Buren in Corrientes province in northeastern Argentina, where up to nine fly species have been found to co-occur. Males of P. tricuspis and P. obtusus were the only males normally attracted to disturbed fire ant colonies.