Researchers are raising warnings about genetically engineered corn that makes its own pesticide, giving new perspective to concerns about a development meant to reduce the need for chemical pesticides.
The corn's toxin is supposed to kill only the pests it's aimed at. But lab tests have shown that the roots exude the poison into the soil where it can remain indefinitely.
Other recent studies have found that the pollen of such genetically altered corn can kill monarch butterfly larvae, and that lacewings - natural predators of insect pests - die when fed corn borer worms raised on the plants. Critics discounted such findings as unnatural laboratory conditions unlikely to prevail on the farm.
The new warning published today in the journal Nature also springs from the test-tube. But this time, the findings identify a phenomenon that can directly affect farmers' fields. It is "very definitely" a concern, says microbiologist Guenther Stotzky of New York University, who reported the discovery along with his colleague Deepak Saxena and Saul Flores of the Venezuelan Institute of Scientific Investigations.
The corn produces the active part of an insecticide made by the bacterium Bacillus thuringiensis. The toxin appears in the leaves, stock, pollen, and roots. When it's ingested, caterpillars stop eating and die.
Soil bacteria destroy the toxin if they can get at it. Dr. Stotzky and his colleagues found that the poison binds to clay particles and humic acids found naturally in most soils. Instead of disappearing in about 25 days, it is active for at least 234 days.
The scientists note that pollen falling on the ground and corn stocks plowed back into the soil add to the toxin that roots exude. They don't know if build-up would continue or level off.
Bt corn toxin is different from Bt sprays widely used as an alternative to chemical insecticides, Stotzky explains. The latter are crystals that only become active in the target insects' digestive systems. That's why they don't harm other creatures.
The corn carries a gene that produces the active form of the poison, which puts pressure on soil organisms. No one knows the consequences, Stotzky says, but "we should stop at this point and consider these things."
He may get his wish. The US and other countries use Bt corn widely, but it is falling out of favor with growing consumer resistance to foods derived from crops genetically modified to carry alien genes (so-called GM foods). Some major food companies insist that suppliers segregate GM crops. Non-GM corn now fetches premium prices.
(c) Copyright 1999. The Christian Science Publishing Society