Effects of exposure to event 176 Bacillus thuringiensis corn pollen on monarch and black swallowtail caterpillars under field conditions

The widespread planting of corn genetically modified to produce Bacillus th uringiensis endotoxin has led to speculation that pollen from these fields might adversely affect nearby nontarget lepidopterans. A previous study of Bt corn engineered with Monsanto event 810 failed to detect an effect of po llen exposure on the black swallowtail, Papilio polyxenes, in either the fi eld or the laboratory. Here, we report results of a field study investigati ng the impact of exposure to pollen from a Bt corn hybrid containing Novart is event 176 on two species of Lepidoptera, black swallowtails and monarch butterflies, Danaus plexippus. Nearly half of the 600 monarch larvae died w ithin the first 24 h; this and subsequent mortality was not associated with proximity to St corn and may have been due in part to predation. Survivors hip of black swallowtails was much higher than that of the monarchs and was also independent of proximity to the transgenic corn. However, despite fiv e rainfall events that removed much of the pollen from the leaves of their host plants during the experiment, we observed a significant reduction in g rowth rates of black swallowtail larvae that was likely caused by pollen ex posure. These results suggest that Bt corn incorporating event 176 can have adverse sublethal effects on black swallowtails in the field and underscor e the importance of event selection in reducing environmental impacts of tr ansgenic plants.