Are crops genetically altered to resist insects really better for the
environment?
In 1985 scientists inserted genetic information into tobacco plants that
enabled them to produce a crystal that was toxic to butterflies, moths
and other insect pests. Derived from the bacterium Bacillus
thuringiensis, the Bt toxin has since been engineered into crops from
corn to cotton, because it is lethal to pests yet seemingly harmless to
other insects and animals, including people. Now a new review of 42
field experiments indicates that fields planted with Bt crops have more
insects and other critters than those treated with broad-spectrum
insecticides. But it also exposes holes in the available research, such
as the impact of genetically modified crops on neighboring ecosystems.

Biologist Michelle Marvier of Santa Clara University in California and
her colleagues found that Bt corn and cotton that were not sprayed with
pesticides had more fauna than treated traditional crops. "What the
study really tells us is that conventional insecticides kill nontarget
insects," says entomologist Bruce Tabashnik of the University of Arizona
(U.A.) in Tucson, who was not involved in the study. The question
becomes, he adds: "Do Bt crops reduce insecticide use?"

The study also reveals, however, that Bt crop acreage has less insect
biodiversity than untreated fields. "It is unclear whether the reduced
abundance of these [insect] groups (coleopterans, hemipterans and
hymenopterans) is due to direct toxicity or is a response to reduced
availability of prey in Bt crops," Marvier's team reports today in
Science.

U.A. entomologist Yves Carri?re, who was also not involved in the study,
notes that farm practices will ultimately determine the value and impact
of such genetically modified plants. "If broad-spectrum insecticides are
commonly used and Bt crops reduce such use, then Bt crops could have
positive impacts,'' he says. "If insecticides are rarely used, then Bt
crops do not bring advantages, and it is still unclear whether they may
bring significant disadvantages."

Previous studies have indicated that Bt crops could lead to increased
use of narrowly targeted pesticides. But they also show that they have
reduced use of the most damaging broad-spectrum insecticides, which
could be good news considering that an estimated 71 percent of U.S.
cotton fields are treated with them, according to U.S. Department of
Agriculture data from 2005.

"It's not just [that] the percentage of the acreage treated is higher,
it's that the use per acre is more intense," Tabashnik notes. "If you've
got Bt cotton, you've got a bigger potential to reduce insecticide use."
Tabashnik also says that studies to determine the impact of genetically
modified crops on creatures great and small in surrounding nonfarm
environments are now needed. "How do transgenics affect wildlife in
native habitats in the U.S.?" he asks. "That is the next frontier in
this environmental assessment."

www.checkbiotech.org