Monarch butterflies, corn pollen coexist in ...( MINNEAPOLIS / ST. PAUL--Milkweeds growi...)

MINNEAPOLIS / ST. PAUL--Milkweeds growing in cornfields sometimes support monarch butterfly larvae at the same time the corn is shedding its pollen, according to a survey of cornfields in the Midwest, Maryland and Ontario. The overlap implies that monarchs feeding next to corn genetically engineered to contain the insecticide known as Bacillus thuringiensis (Bt) toxin could be exposed to the toxin. The study, led by University of Minnesota ecologist Karen Oberhauser, is published on the Proceedings of the National Academy of Sciences Web site, www.pnas.org/papbyrecent.shtml, along with other papers dealing with monarchs and Bt toxin. The series of papers address the issue of whether "Bt corn" is harmful to monarchs in the field as well as in the laboratory.

"We still don't have the data to come to the conclusion that the risks are negligible," said Oberhauser, a research associate in the department of ecology, evolution and behavior.

The researchers examined milkweed and monarch densities in various habitats--cornfields, cornfield edges, other agricultural fields and nonagricultural fields--in the butterfly's breeding range during summer 2000. The study area comprised 20 plots in four regions: Minnesota and Wisconsin, Iowa, Maryland, and Ontario. Plots were in cornfields, land adjacent to cornfields or nonagricultural land, all containing milkweeds. Except for one plot each in Maryland and Iowa, cornfields contained nonBt corn. Every week, researchers examined several hundred milkweed plants and noted the number of monarch larvae and, in cornfields, whether pollen was being shed.

In Minnesota and Wisconsin, corn pollen was shed during a time--mid-July through the first week in August--when the highest numbers of monarch larvae were in cornfields. In Iowa, pollen was shed during the first half of July, before the peak in monarch larvae.

"The situation in Iowa is less risky for mona
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Contact: Deane Morrison
morri029@umn.edu
612-624-2346
University of Minnesota
21-Sep-2001

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