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Bt and the Monarch Butterfly

The monarch butterfly is one of the most recognized and beautiful butterflies found in North America. It has four distinct life stages: egg, larva, pupa and adult butterfly with the larvae entirely dependent on the common milkweed for food. Initial U.S. laboratory studies conducted in 1999 found that the mortality rate of monarch larvae increased when fed milkweed leaves that were dusted with Bt pollen. A collaborative research effort across the U.S. Corn Belt and Ontario (University of Guelph) was undertaken to address the potential questions this study posed. These studies expanded on the extensive risk assessment already completed for Bt corn on non-target insects, but also specifically addressed the impact of Bt pollen on the monarch butterfly and other caterpillar species. The main conclusions from the subsequent studies were that Bt corn hybrids grown in Ontario and throughout the Corn Belt of North America pose a negligible threat to monarch butterfly larvae.

Final Report on the Ecological Impact of Bt Corn Pollen on the Monarch Butterfly in Ontario can be found at:

Full details on the research conducted can be found at: