It is not known whether monarch larvae can avoid eating pollen on a milkweed in a natural environment or whether corn pollen is evenly distributed on all leaves on a milkweed. No studies have been conducted to assess the actual mortality of monarchs on milkweed near cornfields. The answer to this question is not known. Bt 11 and event 176, respectively. Therefore, it is not known how pollen from other Bt events might affect monarchs.
Monarchs prefer to fly in open areas.
In the book, The Monarch Butterfly, F. A. Urquhart states that monarchs locate milkweed by sight and prefer to lay their eggs on small milkweed plants 3 to 18 inches in height. The female butterfly will most easily find these small plants in fencerows, ditches, pastures, and on rough ground. It is unlikely that very many eggs will be laid on milkweed in tall corn. The potential problem with Bt pollen is that it can drift and land on milkweed outside a cornfield. Monarchs that are feeding on milkweed closest to a Bt cornfield would likely suffer the greatest mortality because of a higher concentration of Bt pollen.