Concerns Raised Over Toxin-Producing Crops

For several years now, seed producers have been using genetic engineering to produce corn and cotton varieties that are toxic to pests.

Companies like Monsanto and Novartis have developed so-called transgenic cotton and corn that contain the genes for natural insecticides produced by a bacterium called Bacillus thuringiensis--”Bt” for short. Organic farmers have been using these bacteria for more than 30 years as an alternative to chemical pesticides.

The new Bt corn and cotton, however, are able to manufacture bacterial toxins by themselves--in theory eliminating or greatly reducing the need for pesticides.

But there are potential problems in this genetic Garden of Eden, says UC Riverside professor Brian A. Federici in the latest edition of California Agriculture.

The mature plants don’t always produce enough of the insecticides to ward off pests. This year, for example, Bt cotton growers in Australia had problems controlling caterpillars late in the season and had to apply other pesticides.

And Federici worries about the first generation of these genetically engineered plants, which typically contain only one of several toxic Bt proteins. Although there is no firm evidence that it has happened yet, he is concerned that insects may develop resistance to the toxins, just the way germs become resistant to antibiotics.

He describes several strategies for avoiding such resistance. One approach, now required by the U.S. Environmental Protection Agency, is to plant a mix of Bt and non-Bt plants to provide a refuge for insects that have not developed resistance to the pesticide. That is intended to keep the ratio of pesticide-resistant insects in the population low. Another approach is to implant the genes for several Bt toxins in the plants--increasing their ability to kill the insects that feed on them.