Under natural conditions, monarch larvae feed primarily on milkweed. Most researchers consider it likely that most milkweed does not grow close enough to corn fields to be exposed to significant amounts of corn pollen. Further, the majority of monarch larvae feed on milkweed when corn pollen is not present. Based on known migration behavior, even in those regions in which corn and monarchs co-habitate, only a small portion of the monarch population will be present when corn is shedding pollen. Even if exposed to corn pollen, monarch caterpillars should have no trouble avoiding small amounts of windblown pollen and most likely would do so, as the Nature study suggests.
Milkweed has many large leaves, and it tends to grow in clumps.
If upper leaves were coated with pollen, the caterpillars would most likely move to lower, protected leaves or to another plant, according to Dr. Warren Stevens, senior curator of the Missouri Botanical Garden. For any harm to occur, the monarch larvae have to be emerging and feeding at the same time corn is pollinating, a narrow period of seven to 10 days. Pollen has to be on a particular leaf that the caterpillar is feeding on. And the caterpillar has to consume the pollen before rain or dew washes it away. The caterpillar also has to keep eating, not spit it out and move to another leaf, as the Cornell study suggests will happen in nature.