Microdistribution of immature African blackflies resulting from water velocity and turbulence preferences

Abstract

1. The velocity preferences of larval and pupal blackflies were studied experimentally by comparing the colonization of plastic strings placed in different velocity ranges; and also by investigating the simuliid microdistribution under natural conditions in the river. This required a novel method described for taking spot measurements of water velocity. 2. Simulium mcmahoni de Meillon, S. hirsutum Pomeroy and S. cervicornutum Pomeroy were most abundant in slow velocities (0.3-1.0 m s-1), S. colasbelcouri Grenier & Ovazza and S. hargreavesi Gibbins preferred 1.1-1.8 m s-1, S. squamosum Enderlein and S. vorax Pomeroy 1.9-2.2 m s-1. 3. The larvae of S. hargreavesi and S. cervicornutum preferred a higher velocity range compared with their pupae. 4. In moderate velocities (1.1-1.4 m s-1), the abundance of S. hargreavesi was greater under turbulent conditions than in smooth-flowing water, but this was reversed at very high velocities (2.3-2.6 m s-1). 5. Velocity had no apparent effect on substrate preference when substrates of different flexibilities were compared for three blackfly species. All avoided the most flexible substrates and preferred ones consisting of rigid articulating plates. Anisopteran predators were found to have a similar substrate choice.

The water velocity preferences of Austrosimulium furiosum and Simulium ornatipes (Diptera: Simuliidae) larvae, and the implications for micro-habitat partitioning

“…The precise positioning of larval simuliids within preferred velocity ranges enables microhabitat partitioning to occur (Roberts & Okafor, 1987). This has implications for field studies, as the precise location on the stream bed from which a sample is collected will influence the species obtained.…”

“…Simuliid larvae occur naturally in streams throughout the world, and are known to select areas exposed to specific current velocities (Phillipson, 1956;Ross & Merritt, 1978;Colbo & Moorhouse, 1979;Roberts & Okafor, 1987). They are commonly found in the streams of south-eastern Australia, and often comprise a significant proportion of the stream fauna at some sites (e.g.…”

Micro-distribution of freshwater snails before and after water flow events in hydraulic structures in Tessaout Amont irrigation system, Morocco

“…Understanding snail microecology is essential in identifying the key factor(s) that could be modified to render habitats unfavourable to the intermediate hosts. In contrast to the considerable literature on micro-habitat ecology for other aquatic invertebrates and vertebrates (Bournaud and Cogerino 1986, Roberts and Okafor 1987, Morin and Peters 1988, Quinn and Hickey 1994, Harmelin-Vivien et al 1995, few studies have focused on snail micro-ecology (Scorza et al 1961, Thomas and Tait 1984, Utzinger et al 1997.…”

Evaluation of Partially Submerged Sticky Traps On Lake Spillways For Adult Black Fly (Diptera: Simuliidae) Surveillance and Arbovirus Detection

“…Physical manipulations of spillway flow can alter black fly species assemblages and inhibit breeding (Jobin 2003). Previous studies have observed species-specific water velocity preferences, specializing and exploiting various lotic microhabitats (Roberts and Okafor 1987). High water velocity from spillways will clear plant debris used by gravid females to oviposition, thus reducing egg laying.…”