Diversity, Seasonal Activity and Habitat Associations of Robber Flies (Diptera: Asilidae) in West-Central Illinois

Abstract

Robber fly diversity, seasonal activity and habitat associations were studied in prairie and forest habitats in west-central Illinois from May to Oct. 2005. The greatest numbers of individuals and species were collected in recently burned prairie and forest habitats, although richness in the recently burned prairie was lower than expected based on rarefaction. Six of the eight most abundant species had primarily mid-season or earlier flight activity patterns; the other two species were mid- to late or late season fliers. There was significant variation in robber fly species composition among habitats. Forest habitats had greater within-habitat variation in species composition than did prairie habitats. Three indicator species (Cerotainia macrocera Say, Nerax aestuans (L.) and Promachus hinei Bromley) were found, all for prairie habitats. Two species (Ommatius ouachitensis Bullington & Lavigne and P. hinei) showed significant sex-related variation in habitat associations. These results show that significant variation in robber fly assemblages can occur over relatively small geographic areas and that fire may affect robber fly abundance and diversity.