There is some positive news for the Monarch butterfly from the Obrycki study. Those larvae that survive even high doses of Bt-containing pollen go on to develop to maturity and reproduce normally. Additionally, current field studies are looking to see if butterflies are laying their eggs at the same time that corn plants are naturally pollinating. Even in areas where there is an overlap in time when migrating butterflies lay their eggs and the normal two-week pollination period in corn fields, field studies show that the level of pollen outside the corn fields drops off rapidly from the edge of the fields. Given a choice, butterfly larvae will not eat pollen with or without Bt.
Bt corn is designed to fend off the European corn borer.
The European corn borer is far more sensitive to Bt from transgenic corn than the monarch or swallowtail butterflies. Bt naturally occurs in soil and is sprayed frequently by organic and conventional farmers to control pests such as the European corn borer. EPA completed this evaluation prior to allowing the Bt-containing plants to be grown on a large scale and before the Bt corn could be marketed. In a July 2000 ruling by the Washington D.C. Court of Appeals, the EPA was found to be prudent in its evaluation of Bt-containing crops. As predicted, laboratory studies such as those conducted by Losey and Obrycki, demonstrate that the monarch butterfly larvae prefer leaves with no pollen, but when given no other food the larvae will eat the pollen.