Although toxicity and exposure studies have shown that Bt-corn pollen poses little to no risk to the monarch butterfly, questions remain about the effects of Bt-corn anthers. In 2002, laboratory bioassays were conducted with three treatments: milkweed leaves with Bt anthers, non-Bt anthers, and no anthers. Larvae exposed to Bt anthers in the lab fed less, weighed less, had longer developmental times, shorter life spans, and higher mortality than larvae that were not exposed to anthers. In 2002, studies were conducted to test for adverse effects under field exposure conditions. There were ten replications of three treatments: individually-potted common milkweed with Bt anthers, non-Bt anthers, and no anthers. Milkweeds were placed in a section of detasseled corn. Five larvae were placed on each plant and, for treatments with anthers, five anthers were placed on each leaf. Milkweed plants then were caged with no-see-um netting to exclude predators. For 2002, there were no significant differences in larval, pupal, or adult weights, days to pupation, or life span. The field exposure tests were repeated in 2003 to test for year-to-year consistency. Laboratory data showed that monarch larvae were adversely affected when forced to encounter a high density of anthers. The field data from 2002 showed no adverse effects, suggesting low exposure to anthers in the field. Results from 2003 field studies will be presented.
Species 1: Lepidoptera Danaidae Danaus plexippus (monarch butterfly)
Keywords: risk assessment, non-target species
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