BRIEFING PAPER No.8
Insect-resistant Plants: New Risks Emerging to Non-target Species
Tappeser, Dr. Hartmut Meyer
Several plants are being genetically engineered to make them toxic to insect pests. Two recent pieces of research have shown negative effects of insect resistant plants on beneficial, non-target insects.
One strategy is to genetically engineer Bacillus thuringiensis endotoxin genes (Bt) into crops, for example to be toxic to larvae of lepidopterian pests. Larvae of the cornborer intoxicated by feeding on maize containing Bt were found to be poisonous to lacewing flies. Lacewing flies are beneficial insects as they are predators of lepidoptera larvae and are important for reducing these parasites in crops.
In experiments done at the Swiss Research Station Zurich-Reckenholz, two out of three lacewing flies died when they were fed on the cornborer larvae which had eaten Bt maize. Even some larvae of another species (African cottonworm) which are not normally poisoned by Bt toxin but which had taken up the endotoxin were fatal to lacewing flies.
Another strategy to create insect resistance is to integrate genes of protease inhibitors (PIs), which are small proteins that interfere with enzymes in the intestinal tracts of insects. These PIs have the potential to induce development disruption and increased larval mortality in a large range of insects, not differentiating between pests and beneficial insects. As a result, bees and other pollinators can be exposed to PIs through pollen and nectar. Researchers at the National Institute for Agricultural Research in France (INRA) investigated the effects on honey bees. They fed elevated levels of PIs together with a sugar solution to bees for three months and found that such bees died 15 days earlier than bees fed normal sugar. Another effect was that after only 15 days of ingesting PIs, bees had problems to distinguish between the smells of different flowers. The research concluded that negative effects of long-term exposure to PIs on the survival and behavior of honey bees cannot be excluded.
So it seems that genetically engineering PI plants as a pest control strategy can well destabilise important plant-insect interactions which are vital for the maintenance of plant productivity and reproduction.
F. & M. Keller. [Risk assessment with genetically engineered Bt-maizel],
in German, press release No. 11 of FAL, Zurich-Reckenholz, 9-11-1997
Montreal, 15 October, 1997