Meeting Abstract
Neonicotinoids are commonly used pesticides in U.S. agriculture. For many beneficial insect species, lethal effects of neonicotinoids are well-documented; however, much less is known about sublethal exposure. The alfalfa leaf cutter bee Megachile rotundata is a managed pollinator that constructs complex nests for its young. Nest construction requires a sequence of behaviors that could be affected by neonicotinoid exposure even when dosages are sufficiently low to avoid mortality. Our goal was to determine whether sub-lethal neonicitinoid exposure alters nest construction in adult female M. rotundata. We first determined the LD50 of imidacloprid—a common neonicotinoid used in alfalfa and other M. rotundata-pollinated crops. We observed lethal effects at doses of ~50ppm, which was lower than previously determined through topical application. Nesting success was measured by releasing adult females into field cages after exposure to 1ppm imidicloprid in sucrose solution (treatment) or sucrose solution (control) for 24 hours. Treated females did not complete any nests while control females built significantly more fully completed nests. We then performed an acetylcholinesterase assay to measure the duration of imidacloprid intoxication. However, we observed no upregulation of acetylcholinesterase activity following imidacloprid exposure. Thus, sub-lethal doses caused behavioral effects without enzymatic upregulation of acetylcholinesterase. In conclusion, these results suggest a higher sensitivity to neonicotinoids than previously suspected for M. rotundata, including substantial consequences on nest-building behavior.
