Diversity of saproxylic Cecidomyiidae (Diptera) in a Quebec hardwood forest

The diversity of saproxylic Cecidomyiidae (Diptera) associated with decaying logs was studied in an old-growth forest on Mont Saint-Hilaire, Quebec from June until September 2004. More than 24 000 specimens representing 323 species and morphospecies were collected in emergence traps set over American beech or sugar maple logs in two different stages of decay. The paedogenic species Miastor metraloas Meinert was by far the most numerous species with 17 002 individuals and was excluded from further analyses. Most of the remaining species were fungivores, detritivores or predators. Significantly more specimens were collected in logs in the more advanced decay stage, and indicator species analysis showed that the most abundant species were associated with this decay stage. Overall species richness was not significantly different between decay stages or tree species; however, non-metric multidimensional scaling indicated that the species assemblages associated with decay stage and tree species were significantly different despite the similar species richness.