Tuesday, May 27, 2008
275

Limnephilid caddisflies of summer–dry streams in a western Oregon agricultural landscape

William J. Gerth, Judith L. Li, and Richard Van Driesche. Department of Fisheries and Wildlife, Oregon State University, 104 Nash Hall, Corvallis, OR 97331

We sampled macroinvertebrates from 18 summer-dry, agriculturally-influenced streams during winter and spring. All of these streams flowed for 6 months or more per year and their watersheds had 55-98% of land used for agriculture. Surber samples collected in March contained high relative abundances of non-insects and few mayflies, stoneflies and caddisflies. Nonetheless, combining qualitative and quantitative samples, we found limnephilid caddisflies (Heperophylax sp. and several Limnephilus species) at over 90% of sites. Limnephilus larval morphospecies were lab-reared to obtain adults for species identifications. Limnephilus species included L. nogus, L. occidentalis, and L. flavastellus, and a fourth morphospecies that may consist of more than 1 species. Limnephilus nogus was most ubiquitous, occurring at 67% of sites; Hesperophylax sp. was least common, found at only 3 sites. Limnephilus nogus was common in the more agriculturally-influenced sites east of the Willamette River and the undetermined Limnephilus morphopsecies was common in the less agricultural sites west of the Willamette; these types only co-occurred at 3 sites. Limnephilus flavastellus and L. occidentalis were also segregated, co-occurring at only 2 sites. Species identifications allowed us to document the regional limnephilid diversity that persists despite extensive agricultural land use and to better understand within-region caddisfly distributions.


Web Page: Limnephilidae, summer–dry streams, agriculture