Low Risk of Bt Corn Pollen Killing a Non-target Butterfly

Bill Hutchison, Extension Entomologist, University of Minnesota

Unlike the laboratory study with the Monarch butterfly, published in May 1999, a recent field study (June 6, Proc. Nat. Acad. Sci.) with another common butterfly, showed very low risk of mortality due to Bt corn pollen. C. L. Wraight and colleagues at the University of Illinois, found that the Black Swallowtail butterfly, Papilio polyxenes, which can be common near Midwestern corn fields, showed little sensitivity to Bt corn pollen, when feeding on leaves exposed to pollen concentrations typically found in the field. The eastern black swallowtail occurs throughout North America, where larvae feed on a variety of hosts in the carrot family (Apiaceae), including Queen Anne's lace and parsley. This species is commonly observed in pastures, and along roadsides or edges of cultivated fields in the Midwestern USA

With the onset of pollen shed, potted host plants were infested with first-instar swallowtail larvae and placed at various intervals from the edge of a field of Bt corn (Pioneer 34R07, with the MON810, Monsanto event; Cry1Ab Bt toxin). Corn pollen collected on the host plants was confirmed to contain Cry1Ab toxin, (approx. 2 ng/g). Although many larvae died during the experiment, there was no relationship between mortality and proximity to the field, or to pollen deposition on the host plants. In addition, pollen from these same plants failed to cause mortality in the laboratory at the highest pollen dose tested (10,000 grains/cm²). The researchers conclude that the Bt pollen of this hybrid (Bt event) is therefore unlikely to affect wild populations of black swallowtail, one of the key "non-target" lepidopteran species in the Midwestern USA. For more detail regarding this study, check the following article: http://www.pnas.org/cgi/content/abstract/130202097v1

Co-Editors: Bill Hutchison, Department of Entomology, University of Minnesota, hutch002@tc.umn.edu
Jeanne Ciborowski, IPM Program, Minnesota Department of Agriculture, jeanne.ciborowski@state.mn.us
Cindy Tong, Department of Horticulture, University of Minnesota, ctong@extension.umn.edu
Production Editor: Suzanne Wold, Research Specialist, University of Minnesota, woldx018@tc.umn.edu

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Last Revised June 29, 2000.
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