Seasonal patterns of activity among species of black fire ant parasitoid flies (Pseudacteon: Phoridae) in Argentina explained by analysis of climatic variables

Abstract

Abstract We monitored weekly relative abundances of adult female Pseudacteon (Diptera: Phoridae) species between February 1998 and May 2000 in Argentina. Fire ant-phorids were active around mounds of Solenopsis richteri Forel throughout the year. Phorid species richness ranged from six species during the summer-fall, to a single, large species during the winter. Species were classified as winter, summer, or fall-spring species, depending on times of peak mean abundance. We used descriptive multivariate techniques to analyze phorid phenological data (correspondence analysis), climatic data (principal component analysis), and their relationships (canonical correspondence analysis=CCA) at three temporal scales. The long-term mean temperatures, the mean and minimum sampling-time temperature, and the cumulative number of days without rain from the two months preceding each sampling day explained >90% of the variance when the data for sampling dates were averaged across the same months over the two years. Pseudacteon borgmeieri Schmitz, the winter dominant, was associated with lower temperatures and rainfall, whereas Pseudacteon curvatus Borgmeier, the summer dominant, showed the opposite pattern. Among the fall-spring species, Pseudacteon comatus Borgmeier was associated with months of higher maximum temperatures, longer photoperiods, and lower relative humidity. Pseudacteon nudicornis Borgmeier, in contrast, showed the opposite pattern. Pseudacteon tricuspis Borgmeier, was associated with months, typically in fall, having greater rainfall and fewer days with frosts. Implications of these patterns for the process of selecting particular species of S. richteri-attacking Pseudacteon for use in biological control introductions against imported fire ants are discussed in relation to climates of source and release areas.