Effects of Bt corn pollen on caddisfly growth rates in Midwestern agricultural streams

Jillian D. Pokelsek¹, Emma J. Rosi-Marshall, PhD², Catherine P. Chambers³, Natalie A. Griffiths⁴, Michelle A. Evans-White, PhD⁵, Jennifer L. Tank, PhD⁴, Matt R. Whiles, PhD⁶ and Todd V. Royer, PhD⁷, (1)Biology, Loyola University Chicago, Chicago, IL 60626, (2)Biology, Loyola University Chicago, 6525 N. Sheridan Rd., Chicago, IL 60626, (3)Department of Zoology and Center for Ecology, Southern Illinois University, Life Science II, Carbondale, IL 62901, (4)Biological Sciences, University of Notre Dame, Department of Biological Sciences, Galvin Life Science Center, Notre Dame, IN 46556, (5)Biology, Kansas State University, Division of Biology, Manhattan, KS 66506, (6)Zoology, Southern Illinois University, Southern Illinois University, 326 Life Science II, Carbondale, IL 62901, (7)Environmental Science, Indiana University, 1315 East Tenth Street, SPEA 310, Bloomington, IN 47405

Midwestern agricultural fields are often planted with transgenic Bt corn, which contains toxins that target lepidopteran pests. Filter-feeding caddisflies are closely related to lepidopterans and can be abundant in these agricultural streams, representing an important component of stream food webs. Our previous research demonstrated that filtering caddisflies consume corn pollen and we hypothesized that they may be adversely affected by endotoxins in Bt corn pollen. To address this hypothesis, we developed flow-through chambers to measure individual growth rates in situ. In July 2006, we measured growth rates of Hydropsyche and Cheumatopsyche caddisflies in three streams draining fields planted with Bt corn and three with non-Bt corn in Benton County, Indiana. We deployed hydropsychids in growth chambers (40-60 individuals per site) for 7-9 days and calculated individual growth rates. Instantaneous growth rates ranged from 0.024-0.059 d^-1 and mortality averaged 33%. The presence of Bt corn pollen did not influence growth or mortality. Results of this particular study do not indicate that Bt corn pollen poses a threat to filtering caddisflies. However, caddisflies in our study were exposed to relatively low concentrations of pollen and further research is needed to assess potential adverse effects of Bt corn pollen on other stream-dwelling invertebrates.