Murray H. Colbo

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

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.

The effects of sampling technique on the ecological characterization of shallow, benthic macroinvertebrate communities in two Newfoundland ponds

The influence of sampling technique on the characterization of benthic macroinvertebrate communities on boulder-cobble substrate in two shallow freshwater ponds was analysed. Sweep-net and rock-bag sampling techniques were used to collect macroinvertebrates from two ponds in Newfoundland, Canada. Abundance and diversity of macroinvertebrates were compared in relation to the nature of the substrate and the technique. The two sampling techniques provided different estimates of diversity and density of the benthos. Neither method truly represented the benthic community as neither collected all taxa and each method typically over- or under-estimated the abundance of taxa. The difficulty of interpreting such data is discussed, with special reference to the rapid assessment of water quality in biomonitoring studies.

A critical examination of four methods of estimating the surface area of stone substrate from streams in relation to sampling Simuliidae (Diptera)

Four methods of calculating stone surface area are examined for their value in estimating simuliid larval density. All methods produced area estimates highly correlated with each other. Stone surface area poorly correlated with simuliid abundance, which we concluded was the result of a highly variable microhabitat and the inability to estimate the surface area actually occupied by larvae. Therefore, if an estimate of stone surface area is required, the simplest methods are sufficient (e.g., maximum length × 90° maximum width).

INCORPORATION OF FRESHWATER RHODOPHYTA INTO THE CASES OF CHIRONOMID LARVAE (CHIRONOMIDAE, DIPTERA) FROM NORTH AMERICA1

Chironomid larvae incorporate pieces of freshwater red algae into their cases from a wide geographic range in North America, extending from southern Canada to central Mexico. The Rhodophyta used in this process represent two orders (Acrochaetiales and Batrachospermales), five genera (Audouinella, Batrachospermum, Lemanea, Paralemanea, and Sirodotia), and 14 species from 21 locations. Three genera from the chironomid subfamily Orthocladiinae make these cases: Cardiocladius, Eukiefferiella, and Orthocladius. The Eukiefferiella claripennis group was the most frequently observed infrageneric taxon using red algae in its cases. The cases were tubular in shape with longitudinally oriented strips of algae held together by silken threads. Some of the cases constructed with Batrachospermum and Sirodotia also had several lateral branches of the alga radiating from the tube.