Seasonal succession and spatial–temporal distribution patterns of six larval cytospecies of the Simulium venustum/verecundum complex (Diptera: Simuliidae)

Abstract

The seasonal succession of S. venustum/verecundum cytospecies found in both sublacustrine and downstream habitats on the Avalon Peninsula, Newfoundland, was investigated. EFG/C venustum (= Simulium truncatum Lundström) appeared 1–5 weeks earlier than other cytospecies. ACD verecundum (= S. rostratum Lundström) and AA verecundum usually appeared later and remained in streams longer than EFG/C, AC(gb) venustum, CC2 venustum, or CC3 venustum. Seasonal occurrence of sympatric cytospecies often overlapped, though development was typically staggered and population peaks were asynchronous. EFG/C, and probably CC3, are univoltine in Newfoundland. AC(gb) may have a second generation at a few sites. CC2 has two or more generations per year in Newfoundland, though generation number varied among sites. ACD and AA are multivoltine. Proportionally more ACD and AA were found on vegetation than on rocks, whereas the reverse was true for EFG/C. As well, the density of a mixed ACD–AA population was usually higher on vegetation than on rocks. Cytospecies composition at sublacustrine sites was different from sites farther downstream. The results of the present investigation were also combined with those of a previous study on spatial distribution to construct spatial–temporal ecological profiles for four cytospecies (EFG/C, AC(gb), ACD, AA). Each cytospecies showed a distinct profile.