Spatial distribution patterns of larval cytotypes of the Simulium venustum/verecundum complex (Diptera: Simuliidae) on the Avalon Peninsula, Newfoundland: factors associated with occurrence

Abstract

Larval macrodistribution of cytotypes of the Simulium venustum/verecundum complex among 60 stream sites over a limited geographic area (Avalon Peninsula, Newfoundland) was investigated. Cytotypes included EFG/C, ACD, AA AC(gb), and CC2-3 (combined CC2 and CC3). Stream sites were classified into four types: outlets, trickles, small streams, and large streams. Factors that might explain patterns of occurrence (presence or absence) were examined using correlation, frequency, and cluster analyses. The data showed that larval EFG/C and ACD dominated outlet sites. The CC2-3 and AC(gb) cytotypes were most frequent at downstream sites. In downstream locations CC2-3 was found at almost all sites, whereas AC(gb) was most frequently found in cool, canopied streams, where the bottom consisted mainly of small stones and rubble. In the spring AA was most common at outlet sites. In the summer AA was most frequently found at outlets and trickles. The summer generation(s) of AA was associated with the distribution of trailing and emergent vegetation.