TRANSGENIC PLANTS AND INSECTS Effects of Cry1Ab-Expressing Corn Anthers on the Movement of Monarch Butterfly Larvae

Decreased larval feeding and weight of the monarch butterßy, Danaus plexippus L., have been detected after 4 d of exposure in the laboratory to a high density of Bacillus thuringiensis (Bt)-expressing anthers. One hypothesis is that larvae exposed to Bt anthers exhibit increased wandering, resulting in less feeding and lower weight gain. To test this hypothesis, 2-d-old monarch butterßy larvaeexposed tomilkweed leaf diskswithnoanthers, anthers that expressBt (Cry1Ab, event MON810), or other non-Bt anthers were observed using a video-tracking system. As had been shown in previous studies, larvae exposed to Bt anthers fed less and gained less weight than larvae exposed to non-Bt or no anthers, yet there was no evidence of feeding on anthers. Total distance moved, maximumdisplacement from release point, percentage of time spentmoving or near anthers, or mean turn angle did not differ across treatments. However, larvae exposed to Bt anthers spent more time off milkweed leaf disks than those exposed to no anthers and were more likely to move off the leaf than larvae exposed to non-Bt anthers. Results suggest that larvae exposed to Bt anthers behave differently and that ingestionmaynot be the onlywayBt can affect nontarget insects like themonarch butterßy.