Laboratory studies on the biology of Simulium nigritarse Coquillett and Simulium adersi Pomeroy (Diptera : simuliidae)

Abstract

The eggs of both Simulium nigritarse and S. adersi took up to 13 days to hatch in water at a temperature of 25 °C. The larvae of S. nigritarse required a minimum of 20 days and those of S.adersi a minimum of 17 days to pupate when reared in water at 20± 1 °C. No difference between the sexes was observed in the time taken by the larvae of either species to complete their life cycle. The duration of the pupal stage of S. nigritarse ranged from a minimum of 47 hours at 25 °C to a maximum of 569 hours (23,7 days) at 6 °C. An ambient temperature of 30± 1°C was lethal for both the larvae and the pupae of S. nigritarse. Eclosion of S. nigritarse reaches a peak after sunrise, then the rate declines towards sunset. A mean of 76% of the flies were found to hatch during the day. The time of eclosion of both males and females was similar. Pupation of S. nigritarse could take place at a water-depth of 2m and was common at a depth of 1,1 m. In still water no negative geotropism could be detected in the behaviour of S. nigritarse larvae and they were positively phototropic. In agitated water larvae did not respond to a light gradient ranging from 5 to 1100 lux. Adult larvae became negatively phototropic before the onset of pupation, which took place in dark, fast-flowing water. S. nigritarse can overwinter in both the larval and the pupal stages.