Chironomids (Diptera) typically comprise the most abundant group of macroinvertebrates collected in water quality surveys. Species in the genus Cricotopus display a wide range of tolerance for manmade pollutants, making them excellent bioindicators. Unfortunately, the usefulness of Cricotopus is overshadowed by the difficulty of accurately identifying larvae using current morphological keys. Molecular approaches are now being used for identification and taxonomic resolution in many animal taxa. In this study, a sequence-based approach for the mitochondrial gene, cytochrome oxidase I (COI), was developed to facilitate identification of Cricotopus species collected from Baltimore area streams. Using unique COI sequence variations, we developed profiles for seven described Cricotopus sp., four described Orthocladius sp., one described Paratrichocladius sp. and one putative species of Cricotopus. In addition to providing an accurate method for identification of Cricotopus, this method will make a useful contribution to the development of keys for Nearctic Cricotopus.

1) Functional response curves were constructed for Celithemis fasciata larvae feeding on 6 different densities of midge larvae at 10, 15, 20, and 25°C. Values for attack rate and handling time were estimated with Rogers's random predator equation. 2) Polynomial regression revealed that the functional response curves were linear although a tendency toward decreasing consumption rates at higher densities was shown. 3) The mean number of prey eaten increased with temperature; however, temperature did not alter the fundamental shape of the functional response curve. 4) The attack rate and handling time were linearly related to temperature in general, but changed relatively little between 15 and 20° C.

In a longitudinal study of two streams whose lower reaches received unattenuated urban stormwater runoff, physical disturbance by stormflow was less important than the persistant unidentified chemical impacts of urban stormwater in limiting the distribution of Chironomidae, and Ephemeroptera, Trichoptera and Plecoptera (EPT). A hierarchical spatial analysis showed that chironomid density did not decrease from rural to urban stream reaches. Instead, the taxonomic composition of chironomid assemblages was significantly altered in urban versus rural reaches; chironomid assemblages in urban reaches exhibited higher average pollution tolerance scores. In contrast, the density of EPT was significantly lower in urban reaches. Despite higher values of stormflow tractive force in urban reaches, streambed stability tended to be greater in urban reaches. Modeling of temporal variation in chironomid density showed similar patterns in both rural and urban reaches: chironomid density had a unimodal relationship to rainfall index (RI), with highest densities at intermediate values of RI. Models of EPT density over time in rural reaches showed no significant relation to RI, and temporal variation in EPT density in urban reaches was not predictable. The abundance of fine particulate organic matter, including periphyton (FPOM), on cobbles was greater in urban reaches and showed a much greater degree of temporal variation than in rural reaches. In urban reaches, a negative relation between FPOM and RI indicated the importance of stormflow abrasion.

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1. Larvae of Pseudochironomus richardsoni were reared to pupation in individual enclosures, in one of three thermal habitats in a northern California stream. The average temperature range in cold seeps was 15–21 °C, while the main channel ranged from 20 to 27 °C, and side pools ranged from 18 to 33 °C. Diet consisted of either diatoms or algal detritus. 2. Specific growth rate ranged from 0.057 to 0.267 day–1. Specific growth and developmental rates were highest on a diatom diet, and increased with temperature. Regressions of growth rate on mean microsite temperature were also significantly altered by diet. Differences in specific growth rate due to diet are magnified at higher temperatures. 3. Pupae reared on diatoms were larger than those reared on detritus. The mass of pupae reared on detritus decreased with increasing temperature. However, there was no significant relationship between pupal mass and temperature for larvae reared on diatoms. 4. The combined effects of food quality and thermal environment on growth of the midge P. richardsoni are significantly different from the independent effects of diet and temperature. Interactive effects of food quality and temperature may influence the contribution of certain aquatic habitats (algal mats) to invertebrate secondary production.