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Monarch Butterflies and Bacterial Toxins

© Neal Rolfe Chamberlain

Corn is a major food source of cattle. Without corn the beef industry would be in real trouble. Corn is the principle grain used to fatten up cattle just before they are sold. I live just south of Iowa (United States). Iowa is one of the major corn producing states and believe me corn is BIG business. Corn as far as the eye can see. In fact the tallest thing in Iowa during the summer months is the corn plant. Unfortunately, with the corn comes insects that also love to eat corn. The European corn borer and the corn earworm destroy nearly a billion U.S. dollars worth of corn every year. To stop these pests large amounts of pesticides are sprayed on the corn crop. These pesticides kill lots and lots of insect pests and also kill endangered and helpful insects. Pesticides can also be harmful to people. This is a real problem for the environment and for people working in these areas. The spraying of pesticides is also very expensive. A more ecologically sound way of eliminating insect pests would be best for everyone.

One way to avoid spraying pesticides on the corn has been found and is currently being used in 30 percent of the corn crops in the United States this year. It is a genetically altered corn plant that produces an insect toxin called Bt. Bt is a toxin produced by a bacteria called Bacillus thuringiensis. The Bt toxin gene was taken from the bacteria and then placed in the corn plant. The toxin is produced at low levels which is not toxic to vertebrates (animals with a backbone) such as humans, birds, fish, or cattle but will kill the immature forms (larvae) of certain insects. When the European corn borer and the corn earworm larvae eat enough Bt toxin they just stop eating and then die. This is great. No more big losses in productivity due to those nasty pests and the end of spraying pesticides on the corn crop every year.

Unfortunately, other helpful and endangered insects like the Monarch butterfly caterpillar have to eat too. This caterpillar loves to eat milkweed leaves. Milkweed is a common weed in the United States that can be found growing near many corn fields. Corn is a wind pollinator. It requires wind to spread its pollen. The pollen goes everywhere. It lands where ever the winds take it. This pollen also has the Bt toxin in it. If enough pollen lands on milkweed then the Monarch caterpillars could also die.

A paper in a recent issue of Nature by John Losey of Cornell