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Competing hypotheses that try to relate population size, individual weight, and water temperature in running waters were tested. Female and male dry weight and specimen numbers of eleven caddisfly species (Trichoptera) collected from 1983 to 1991 in four emergence traps along the Breitenbach (Germany) were related to site specific water temperatures. Water temperature along the stream showed the classical pattern, almost constant near the source and increasing annual variability downstream. Temperature sum (dd = degree days) increased downstream; sums of the last three, six and nine months had a clear seasonality, twelve months sums were almost constant. Greatest upstream-downstream differences occurred in autumn and winter. Comparison of Trichoptera was based on yearly abundance and weight data. Females were heavier in all species but Potamophylax cingulatus. Among sites, weight differences were not detected for Apatania fimbriata. Silo pallipes, Tinodes rostocki, Plectrocne-mia conspersa and for P. cingulatus (♂) and Rhyacophila fasciata (♂) at least in stream sections where they occurred regularly and abundantly. Weight differences were usually significant only between the uppermost or the lowermost, and the remaining sites along the stream. Sericostoma personatum exhibited an almost site by site weight increase downstream. Drusus annulatus (♂, ♀), R. fasciata (9) and P. cingulatus (♀) were lightest at the downstream site, where only R. fasciata occurred regularly. C. villosa (♂, ♀). Potamophylax luctuosus (♂), S. personatum (♂) and Agapetus fuscipes (♂) were lightest at the uppermost site. No single hypothesis explained all results. High individual and population success (high weight or abundance) as predicted by the 'Thermal Equilibrium Hypothesis' occurred in D. annulatus, P. cingulatus and P. luctuosus. In contrast, high abundance and low weight occurred in C. villosa and S. personatum. Individual success seems to depend on a specific fit of genetic pre-adaptations, appropriate physiographical and ecological conditions, and competitive ability; it is not necessarily connected with population success.

Size, weight and abundance of eleven species of caddisfly collected in four emergence traps from 1983-1991 at the Breitenbach (Germany) were analyzed for spatial and temporal patterns. Scrapers were abundant and small, shredders rare but large, predators were in between. Individual weights of most species increased downstream. No weight change along the stream was detected in A. fimbriata, T. rostocki, P. conspersa and R. fasciata. At low discharge, specimen numbers of A. fimbriata and C. villosa decreased, but it increased in P. conspersa. No correlation between discharge and any weight measure occurred. Intra- and interspecific competition was detected only between the scrapers A. fuscipes, A. fimbriata and D. annulatus, with negative effects on size and weight of other species and of competitors. Similar findings in the shredder C. villosa were effects of site specific temperature patterns, not of direct competition. It was evident that dependencies or interactions discovered at individual sites generally did not occur at all sites simultaneously. Inter- and intraspecific competition for a limited food source was detected only in scrapers during periods of low flow. No effects of food shortage was discovered in shredders or predators. Thus, based on the individual and population success of caddisflies, it is argued that the stream community in the Breitenbach was mainly driven by physical forces, temperature and discharge. Only under particular spatial and temporal conditions competition effects do become evident.

Eversible pleural sacs were recently discovered in ♀♀ of European species of Rhamphomyia Meigen 1822 (Empididae). In live specimens, they are showily orange. SEM photos show a peculiar surface with numerous setae arranged in whorls. It remains unclear whether they are simply decoration or in combination with pheromones to increase female attractivity. Appendages of male Dolichopodinae are digitate and not covered by hairs or setae. They seem to be restricted to the subfamily Dolichopodinae and probably work together with pheromones.

Adults of Chaetopteryx villosa (FABRICIUS) (Trichoptera, Limnephilidae) show marked differences in size and weight between sexes at individual stream sites. Size and weight of females increase with distance from the source of the Breitenbach. By rearing specimens from individual egg masses, differences between sexes were attributed to distinct life histories. Males remained longer in larval instars I to III; females spent a greater proportion of the life cycle in instars IV and V. As a result, females were almost twice the size of males. An in-stream enclosure experiment demonstrated that sex, food quality (fine or coarse particulate organic material; FPOM, CPOM), water temperature and, to a smaller extent, origin of specimens determined the size and weight of the developing adults. However, the percent fat content of males and females was unaffected by these factors. Because FPOM and CPOM in the stream were not limiting, size of the adults was determined predominantly by water temperature. Results of the in-stream experiment agreed well with the size and weight patterns observed over a ten-year period in the stream under investigation (Breitenbach). The amount of nutrients invested in the growth of two males was almost identical to that invested in the growth of one female. Maximum size and weight of C. villosa females occurred at sites with the lowest population densities. This pattern reflected the accumulation of degree days rather than a limitation by increased competition for food.

Twenty nine species of aquatic dance flies (Empididae: Clinocerinae and Hemerodromiinae) were recorded from the Breitenbach (Hesse, Germany) between 1983 and 1993. Although most species emerged in spring and summer, Clinocera (Hydrodromia) stagnalis and C. (H.) wesmaeli were trapped in almost every month. A few species of the subgenus Kowarzia of Clinocera emerged in autumn and early winter. Chelifera pyrenaica had two generations per year in the lower part of the stream, but in the upper reach there was only a spring generation. The distribution pattern along the stream of most of the abundant species was maintained over the entire study period. As an exception, Wiedemannia bohemani was abundant in the middle reach of the stream between 1983-1988, but in the lower reach in 1989-1993. As the amount of Particulate Organic Matter (POM) probably increased the abundance of prey organisms, highest numbers were found in areas with high amounts of allochthonous input. Larvae avoided sandy substrates. Many were found in partly submerged moss carpets on stones, at or below the water level. Females of Hemerodromiinae had higher body weights than males, and specimens in localities near the spring were heavier than those from lower sections of the stream, probably as a result of the temperature pattern of the stream. In Clinocerinae the differences between the sexes, and at different sites, were negligible. Ordination of abundance data, as well as environmental data, showed the dominating influence of 'time' and discharge pattern on the community of aquatic dance flies, and the subordinate influence of water temperature, in a time series of 11 years.