By Laura McGinnis

Non-target insects are probably affected more by conventional insecticides
than by crops that contain genes from the soil bacterium Bacillus
thuringiensis (Bt), according to the findings of a study by Agricultural
Research Service (ARS) scientists and cooperators. The findings were
published recently in Public Library of Science ONE.

Bt crops such as maize and cotton are genetically engineered to produce
insect-specific toxins. They target specific insect pests, but the
researchers wanted to determine how these crops influence non-target insects
in the environment.

To find out, scientists from ARS collaborated with researchers at the
University of Nebraska at Omaha, Iowa State University and the U.S.
Environmental Protection Agency. Steven Naranjo, a research leader at the
ARS Arid Land Agricultural Research Center in Maricopa, Ariz., and Jonathan
Lundgren, an entomologist at the ARS North Central Agricultural Research
Laboratory in Brookings, S.D., contributed to the work.

The scientists compared the abundance of groups of non-target insects. They
first compared the abundance of these insects in Bt crops and non-Bt crops
without any insecticides. They also compared the insect populations in both
types of crops treated with insecticides. And they compared the non-target
insect populations in Bt crops without insecticides versus the populations
in non-Bt crops treated with insecticides.

They formed these groups of non-target insects with data drawn from a
modified version of a public database created by Santa Clara University
biologist Michelle Marvier and colleagues. The toxins examined included
Cry1Ab and Cry3Bb in maize, Cry3A in potato and Cry1Ac and Cry1Ab in cotton.

The researchers observed considerable variability in the effects of Bt
cotton and maize crops on non-target insects. However, the data within the
groups were fairly consistent. The most influential factor was the
insecticide applied. Collectively, insecticides such as pyrethroids,
organophosphates, carbamates and neonicotinoids had larger negative impacts
on non-target insects than did the Bt crops.

The researchers concluded that when it comes to killing non-target insects,
no treatment at all has the least impact. Bt crops have considerably less
impact on non-target insects than do conventional insecticides. Also,
insecticides affect insect populations uniformly, regardless of whether
they're in Bt or non-Bt crop fields.

ARS is a scientific research agency of the U.S. Department of Agriculture.
www.checkbiotech.org