The study was triggered by laboratory work published in May 1999 showing that larvae fed milkweed leaves dusted with Bt corn pollen died. This generated concern that widespread use of Bt corn would harm monarch populations. The EPA ordered further studies on the biology of monarch, the milkweeds it feeds on, and the movement of corn pollen.

The new EPA report found that in most areas monarch larvae are not feeding at the time of year when corn pollen is shed, and that most milkweed grows too far from corn fields to be dusted with significant levels of corn pollen. Also, the report stated that "these products show relatively low toxicity to monarch larvae." 

Bt protein makes corn resistant to moth pests, especially the European corn borer, by poisoning the caterpillars that eat the leaves or stalks of corn. Pollen can also contain the Bt protein, and pollen that falls on leaves of weeds such as milkweeds can poison monarch caterpillars. The type of Bt protein in question works only against moths & butterflies but not against other types of insects or against other animals.

The EPA also cited the projected benefits to monarchs from using Bt crops that reduce pesticide use: "Considering the gains obviously achieved in the level of survival of populations of Monarch butterflies and other insects by eliminating a large proportion of the pesticides applied to corn, cotton and potatoes, some authors are predicting that the widespread cultivation of Bt Crops may have huge benefits for Monarch butterfly survival." 

The EPA will continue to monitor monarch populations as part of its regulation of Bt crops, the report said. The report will reviewed by the EPAâs Scientific Advisory Panel on October 18-20.

For more information: 
Bt Plant-Pesticides Biopesticides Registration Action Document 
www.epa.gov/scipoly/sap/ and then go to: October 18-20, 2000: Issues pertaining to the Bt plant pesticides Risk and Benefit Assessments