Genetic Engineering Kills Monarch Butterflies

May 19, 1999

A study to be published in the May 20, 1999, Nature magazine finds that pollen from genetically engineered corn plants is toxic to monarch butterflies. The corn was genetically engineered to contain a toxin from the bacterium Bacillus thuringiensis (Bt). In 1998, almost 20% of US corn acreage was planted with Bt corn as a means to control insects, and acreage is expected to increase in 1999.

“Bt corn is engineered to contain a pesticide throughout the plant,” said Dr. Rebecca Goldburg, an Environmental Defense Fund senior scientist. “Today’s Nature study clearly demonstrates that the pesticide in Bt corn is dispersed with pollen, killing monarch butterflies.”

Corn plants produce huge quantities of pollen, which dusts the leaves of plants growing near corn fields. The Nature study found that close to half the monarch caterpillars that fed on milkweed leaves dusted with Bt corn pollen died. Surviving caterpillars were about half the size of caterpillars that fed on leaves dusted with pollen from non-engineered corn.

“For too long genetic engineering has been presented to the public as a ‘safe’ alternative to traditional pesticide spraying, but genetically engineered crops are really just being used as a new means to disseminate chemical pesticides. Monarchs that feed on pollen covered milkweed near Bt corn fields might as well be eating pesticide sprayed milkweeds,” said Goldburg. “Either way the result is dead butterflies.”

Monarch butterflies are noted for their remarkable annual migration, which takes them from central Mexico in the winter to as far north as Minnesota in the summer. In the summer months, the Midwestern corn belt is home to about half the US population of monarch butterflies.

“It would be tragic if genetically engineered crops decimated populations of monarch butterflies similar to the way that DDT decimated populations of bald eagles and other birds,” said Goldburg. “The Environmental Protection Agency (EPA), which regulates pesticides, must take action to protect monarchs from poisoning by Bt corn. We urge that the EPA severely restrict farm acreage planted in Bt corn unless and until a plan can be developed to protect butterflies.”