BACKGROUND

The focus of this Figure Set is research done at Cornell University concerning effects of Bt corn on monarch butterfly larvae. Currently, chemical insecticides are used to combat insects that damage or become lethal to crops. However, chemical insecticides often alleviate one problem while creating a new one. Potentially harmful chemicals are being released into the environment that may harm non-target species. This may occur directly through ingestion, inhalation, or absorption; or indirectly through biomagnification and subsequent ingestion or the disruption of an ecosystem which may put strain on various species. Biotechnologists have researched ways to decrease insecticide use. They found that if insecticide resistance were genetically engineered into crops, fewer insecticides would be sprayed onto crop fields. This would lessen the opportunity for some of these chemicals to harm insects, wildlife, humans, and plants.

A strain of the bacterium Bacillus thuringiensis (Bt) is toxic to insects through ingestion (Simmonds & Smartt 1999). This bacterium produces crystal-like proteins (Cry proteins) that selectively kill specific groups of insects. There are several trains of Bt and each have differing Cry proteins. These Cry proteins affect monarch butterfly larvae and some Cry proteins affect the varying species more than others. To create transgenic Bt plants, the specific Bt is isolated and integrated into a crop’s genetic makeup. A plant genetically engineered to express the Bt toxin is resistant to specific insect devastation. For example, the European corn borer (ECB) is very destructive to corn crops. To decrease crop losses, Bt corn was developed through biotechnology and is resistant to ECB devastation. Thus, the level of insecticide treatment can be expected to decrease. Less insecticide use should result in less harm to non-target species. But what if the Bt crop is toxic to non-target species?

Researchers at Cornell University investigated the effect of Bt corn on monarch butterfly larvae. In particular, they looked at the acute toxic effects of Bt corn pollen because this corn pollen may be distributed to nearby plants and ingested by non-target species, such as the monarch butterfly (Losey, Rayor, Carter 1999). This paper was received with substantial criticism and was very controversial. Since the publication of this study, others have sought to verify or refute its implications. Additional figures are from more recent field and laboratory studies by Stanley-Horn et al. (2001) and Hellminch (2001).

Literature Cited:

Hellmich, R. L. 2001. Monarch larvae sensitivity to Bacillus thuringiensis - purified proteins and pollen. Proceedings of the National Academy of Sciences early edition: 1-6.

Losey, H. E., L. S. Rayor, and M. E. Carter. 1999. Transgenic pollen harms monarch larvae. Nature 399: 214.

Simmonds, N. W., and J. Smartt. 1999. Principles of Crop Improvement. Oxford: Blackwell Science.

Stanley-Horn, D. E. et al. 2001. Assessing the impact of Cry1Ab-expressing corn pollen on monarch butterfly larvae in field studies. Proceedings of the National Academy of Sciences 98: 11931-11936.