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Abstract

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 mates. 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.