Adult versus larval assemblage of Trichoptera at an urban headwater stream

The shift from aquatic to terrestrial habitats is a key feature of aquatic insect life cycles.  While watershed urbanization may impact an insect’s entire life cycle, most conservation and restoration efforts focus on in-stream habitat quality and its effect on larval stages.  The terrestrial, adult stage is responsible for reproduction and colonization, and impacts to this stage may contribute to taxa loss from urban streams.  We collected adult and larval Trichoptera with Malaise traps at one urban and one rural headwater to assess the composition of the adult assemblage.  The abundance of adults was similar between streams, but the number of species caught was lower at the urban headwater.  Several species of adult caddisflies at the urban headwater were not found as larvae, indicating that although these species were potential colonizers, poor in-stream quality prevented colonization.  The urban trichopteran assemblage’s low diversity also suggested that watershed urbanization may have limited migration for many taxa typically found in headwater streams.  Impacts to adults and larvae that lead to the loss of populations from urban headwaters differ among species.   Further study is underway to relate these patterns to life history traits of caddisfly species.