Do Biotech Crops Harm Monarch Butterflies?

Yes, it has been shown that pollen shed from some genetically engineered plants can harm butterflies. However, the risk has been proven to be very low, because the varieties that are most harmful are no longer being sold, and more importantly, the risk of exposure to pollen from Bt corn has been shown to be negligible. Certain varieties of genetically engineered corn plants produce a protein called Bacillus thurengiensis (Bt). Known as Bt corn, these plants produce proteins that are only harmful to a limited number of insect species when ingested. Some Bt proteins are only toxic to beetles, while others such as those found in Bt corn kill caterpillars that develop into butterflies and moths. There are many insect pests that feed on crops, resulting in reduced yield. Genetically engineered Bt crops provide resistance to specific pest species. Farmers usually have to spray their fields with insecticides in order to protect their crops, which is also harmful to beneficial insects, other animals, and can in some cases contaminate the environment. With Bt crops, the need to spray is drastically reduced because the insecticidal protein is already in the plant while the environmental contamination and exposure to other organisms is limited.

Some Bt corn types engineered to control the larvae of a common corn pest the European corn borer, can also harm monarch butterfly larvae. Monarch butterfly caterpillars feed exclusively on milkweed plants which grow in and adjacent to corn fields. Initial research indicated that pollen shed from Bt corn would collect on the leaves of milkweed that monarch caterpillars feed on, and caterpillars that consume the Bt corn pollen while eating the milkweed would be adversely affected. However, it has been proven through an extensive series of studies that the risk to monarch butterflies from exposure to Bt corn pollen is minimal for several reasons. The first reason is that pollen shed in most corn growing regions does not coincide with the larval life stage of most monarch butterflies. The second reason, is that the varieties of Bt corn currently available do not express large amounts of Bt proteins in their pollen and the amount of Bt corn pollen need to kill monarch caterpillars does not readily occur in field situations.

Monarch butterflies are threatened by many factors including, weather, predation, and most importantly habitat loss in overwintering sites and summer breeding grounds. Monarchs developing on milkweed within agricultural fields also may be affected by conventional insecticides applied to control pest insects or herbicides that affect the milkweed host. Based on a comprehensive review of scientific information by the U.S. Environmental Protection Agency, it has been concluded that Bt corn pollen does not pose a risk to monarch populations. In 2001, the EPA extended registration of Bt corn products for an additional seven years.