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 Knowledge for the CommonWealth

Concerns Over Impact of Bt on Beneficial Insects

Crop and Soil Environmental News, September 1998

Charles Hagedorn
Extension Biotechnology Specialist

Two recent European studies report troubling and unexpected findings regarding the effects of genetically engineered insect-resistant (Bt) crops on two beneficial insects, green lacewings and ladybird beetles. Scientists from the Swiss Federal Research Station for Agroecology and Agriculture looked at the indirect effects of Bt corn on green lacewing insects that feed on the European corn borer (ECB), the pest targeted by Bt corn. They compared the mortality and developmental rate of two groups of lacewings, one that had been fed ECB reared on engineered Bt corn and another fed ECB reared on nonBt corn.

The experiments revealed that green lacewings fed ECB that had eaten Bt corn had a higher death rate and delayed development compared with lacewings fed ECB that had eaten nonBt corn. More than 60 percent of the lacewings fed Bt corn-reared ECB died compared with fewer than 40 percent of those fed nonBt corn-reared ECB. The researchers suggest that the higher mortality is directly associated with Bt related factors. Among surviving lacewings, those feeding on Bt corn-reared ECB required an average of three more days to reach adulthood than lacewings fed on nonBt corn-reared ECB. The scientists attributed the delayed development to the poor nutritional quality of ECB larvae made sick by the Bt toxin.

In another study, Scottish Crop Research Institute scientists found that ladybird beetles (called ladybugs in the United States) fed aphids reared on transgenic potatoes experienced reproductive problems and failed to live as long as ladybugs fed aphids from ordinary potatoes (the control group). The potatoes were engineered to produce insecticidal lectins, which are proteins from the snowdrop plant that bind to the surface of insect cells causing them to clump and stop functioning. In greenhouse tests, the engineered plants significantly reduced potato aphids, a serious pest of the crop, compared against aphids on non-transgenic potatoes.

The Scottish researchers found that the egg production of female ladybugs fed transgenic potato-reared aphids was reduced by more than one-third compared with the control group. Matings between male ladybugs fed on aphids from transgenic potatoes with females from the control group produced four times as many unfertilized eggs as matings with males from the control group. Nearly three times as many fertilized eggs from females fed engineered potato-reared aphids died before hatching compared with fertilized eggs from the control group. Finally, female ladybirds fed aphids from transgenic plants lived only half as long as females from the control group.

Neither of the studies has been extended to field situations so it is far from clear whether these laboratory results reflect what might happen outdoors. However, if field results show similar deleterious effects on survival, reproduction, and development, of beneficial insects, then long-term impact of large-scale use of transgenic insect-resistant crops on such insect populations will need to be addressed by the scientific and regulatory community.

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