Associations between adult caddisfly species (Insecta: Trichoptera) and stream conditions within the northcentral United States

While use of the emergent adult stage of aquatic insects as stream bioindicators has lagged well behind that of the benthic stage, adult insects of large and diverse taxa such as Trichoptera have great potential for indicating stream conditions. To explore their associations with stream variables, nearly 500,000 adult caddisfly specimens were collected from 798 ultraviolet blacklight samples throughout the northcentral United States. From an original pool of 11 stream characteristic variables, a non-metric multidimensional scaling ordination determined four that were strongly associated with adult caddisfly assemblages: (1) mean summer stream temperature, (2) stream gradient, (3) base flow as a percentage of total flow, and (4) percentage of intact upstream terrestrial habitat. Association values for 209 common species, 60 common genera, and 17 common families from the region are herein presented based on weighted mean specimen abundance and coefficient of variation for each of the four determined variables. While validation of these presented association values using other datasets is necessary to confirm their general utility, this work represents a first step in using adult caddisflies to indicate both natural and anthropogenic stream conditions.