But in Maryland, researchers studied sweet corn, which generally is heavily sprayed with synthetic insecticides as an alternative to Bt corn. They found the caterpillars quickly died in sprayed fields. But in non-sprayed fields, there was no difference between Bt corn and the conventional varieties, said Galen Dively of the University of Maryland in College Park. If not, caterpillars are far less likely to eat the pollen. But researchers in Iowa, Maryland and Kansas found little overlap One finding that cut across all of the studies is that these seemingly delicate butterflies have very tough lives.
Insects devour most of the caterpillars.
The milkweed they depend upon is sprayed by farmers, trampled by deer and mowed by road maintenance crews. Then, of course, there are the long migratory journeys each year to and from Mexico, where their habitat is dwindling. Among other uses, the researchers' findings will be considered by the U.S. Environmental Protection Agency next year as it reviews requests to renew approval for companies to sell several varieties of Bt corn, cotton and potatoes.