Characterizing potential risk of Cry1B.34 and Cry1Da2 proteins expressed in insect-protected maize to monarch...

Declines in monarch butterfly (Danaus plexipplus (Linnaeus)) populations stemming from a variety of causes resulted in the US Fish and Wildlife Service to propose listing monarchs as a "threatened species" under the Endangered Species Act of 1973. The migratory eastern monarch population spends much of the summer months across the Midwest, where a significant portion of the landscape is devoted to agricultural production. Insect-control proteins expressed in genetically modified (GM) maize intended to control lepidopteran pests may exhibit activity against monarch larvae. While monarch larvae do not feed directly on vegetative maize tissue, exposure to insecticidal proteins expressed in GM maize may be possible via inadvertent consumption of GM maize pollen deposited on the surface of milkweed leaves. Previous population-level assessments on insect-protected maize were based on the scenario that monarch larvae were exposed to pollen on milkweed present within maize fields. With modern agronomic practices, milkweed abundance within maize fields has decreased significantly, and the potential exposure of monarch larvae to maize pollen is now limited to milkweed in field margins. Herein, we report the development of a screening-level approach as well as a probabilistic exposure model coupled with explicit landscape information to characterize potential risk of the Cry1B.34 and Cry1Da2 proteins expressed in DP910521 and DAS1131 maize, respectively, to monarch larvae. The results of these analyses indicate cultivation of DP910521 and DAS1131 maize would be unlikely to jeopardize the continued existence of the eastern monarch population were these events to be commercialized in North America.