Larval and pupal microhabitat selection by Simulium truncatum Lundström, S. rostratum Lundström, and S. verecundum AA (Diptera: Simuliidae)

Abstract

Larval and pupal microhabitat selection by the cytospecies Simulium truncatum Lundström, S. rostratum Lundström, and S. verecundum AA was investigated. Last-instar larvae of S. truncatum and S. rostratum selected different microhabitats as shown by their response to velocity, depth, and outlets. Optimal stream velocity for larval S. truncatum and S. rostratum was estimated as 0.36 and 0.69–0.73 m/s, respectively. The microdistribution of S. truncatum showed a parabolic response to outflows with peak abundance occurring between 10.5 and 16.0 m from outlets. The distance-preference curve for S. rostratum was the complete inverse of that for S. truncatum, with maximum abundance of S. rostratum occurring immediately below and 20 m removed from the outlet. Abundance of larval S. truncatum decreased exponentially with depth (0.03–0.34 m), whereas the microdistribution of S. rostratum and a mixed 5. rostratum/S. verecundum AA population was not influenced by water depth (0.03–0.19 m). The microdistribution of pupae was similar to that of last-instar larvae for both S. truncatum and S. rostratum. Although larval microdistribution was influenced by velocity (S. truncatum, S. rostratum) and depth (S. truncatum), it was not possible to explain these patterns in relation to larval size.