Trichoptera agrophiles: characterizing the adult caddisfly assemblages of agricultural streams in the northcentral United States

While most caddisfly species are indicative of undisturbed river systems, some species may instead increase in abundance due to agricultural disturbance. The purpose of this study was to characterize agricultural caddisfly assemblages of the northcentral United States relative to less disturbed streams of the region, and to identify variables potentially important for protecting caddisfly species richness within agricultural landscapes. Over 900 stream sites were sampled for adult caddisflies using ultraviolet light traps within a 1.3 million km2 area. Of these, 308 sites were considered agricultural streams—defined as having upstream land use >82% row crops or pasture. Agricultural streams had significantly lower (~1/3 as much) mean species richness compared to streams least disturbed (<11% of upstream land area) by agriculture throughout all comparable Strahler orders. Of the 305 caddisfly species caught throughout the sampling area, 11 (3.6%) were more abundant in agricultural streams than in less disturbed streams, while several others were common at all disturbance levels. Species of Hydropsychidae and Leptoceridae composed 68% of collection records, 77% of specimen abundance, and 93% of organic biomass of agricultural stream assemblages. Changes in caddisfly assemblages within agricultural streams corresponded to changes in base flow and water temperature, and also to changes in intact riparian habitat. Increases in the last variable also corresponded to increases in species richness within agricultural streams throughout the sampling area. This study provides some of the first data on the caddisfly species assemblages characteristic of agricultural landscapes, and further demonstrates the importance of protected riparian corridors within agroecosystems in preserving aquatic biota.