The ecology of pre-imaginal simuliidae (Diptera) in South-East Queensland, Australia

Abstract

A study of the pre-imaginal simuliid fauna of South-East Queensland was conducted to elucidate some of the aspects of their ecology. A total of 17 species of three genera (Cnephia, Austrosimulium and Simulium) bred in the area. The highest diversity of species was found to occur in mountainous areas near the coast which had the following conditions: high rainfall, steep relief, cool temperatures, on the edge of forests with streams of the order 1–3 (using a 1 : 250,000 map). More detailed studies of A. bancrofti, S. nicholsoni and S. ornatipes were made to investigate microdistribution, colonization, drift, pupation timing and population changes. Current velocity was the most important factor determining the distribution of A. bancrofti, while the distribution of S. nicholsoni was influenced by a preference for vegetation substrate and current velocity. Late instar larvae of A. bancrofti and S. ornatipes occurred in faster currents than early instar larvae. Pupae of these two species primarily occurred on the downstream side of submerged substrates. Colonization of a particular stream was dependent on the oviposition preference of gravid females while drift, looping, or descent on silk threads was used for larval dispersal from the oviposition site. Early instars of A. bancrofti drifted from quiet reaches of mature rivers to rapids, while S. ornatipes larvae appeared to be more sessile with limited dispersal from site of egg masses. Drift occurred throughout 24 hours with little change in total numbers. Early instars of A. bancrofti however showed a definite diurnal tendency while the proportion of late instars increased at night. Pupation of S. ornatipes was diurnal under undisturbed conditions. The larvae of A. bancrofti and S. nicholsoni both developed in the Brisbane River system, however the populations of A. bancrofti peaked in late winter, a dry season with stable water conditions while S. nicholsoni larvae were most abundant from late summer, at the end of the rains to the early winter. The larvae of S. ornatipes, which occur in small streams down to temporary trickles, were most numerous during the warm rainy period.