The relative abundance of pupae of three blackfly species (Simulium spp.) on different diameters of strings

The relative abundance of 3 black-fly species Simulium hargreavesi, S. cervicornutum and S. damnosum s.l. occupying 4 sizes of polythene strings (0.4, 1.5, 2.5 and 5 mm diam.) were studied in the river Assob, Nigeria. An analysis voortof variance showed no discernible substrate preference for S. damnosum s.l. However, S. hargreavesi and S. cervicornutum were most abundant on the large diameter strings, because of their greater surface area available for colonisation. When the abundance per unit area was calculated, the 2 species showed no significant preference for the small, medium and large diameter strings. However, the very small strings were preferred by both species, but especially by S. cervicornutum, despite the mean cocoon size of both species being greater than the string circumference. Cotton string (2.5 mm diam.) was markedly less attractive to all three species.