A new study into the effects that genetically modified Bt corn, engineered to produce a natural insecticide, may have on insects it was not intended to affect has contradicted controversial research on monarch caterpillars last year.
A team from the University of Illinois at Urbana-Champaign, has found the crop has no impact on black swallowtail caterpillars living on weeds alongside cornfields.
The research, published in the latest issue of the Proceedings of the National Academy of Science, comes just over a year after a group of Cornell University scientists reported in Nature that Bt corn caused premature death of monarch caterpillars. This prompted environmentalists to call for the banning of the GM crop.
Bt corn has been modified to carry genetic material that makes the Bacillus thuringiesis toxin, a substance that is fatal to European corn borers, a major pest for farmers.
The latest study involved both laboratory and field tests in which pollen from a crop of Monsanto Bt corn was monitored and measured at a variety of distances from the crop.
May Berenbaum, head of the University of Illinois's entomology department, said: "We found that many caterpillars died but not, as far as we could tell, due to anything connected to the corn or the corn pollen."
However, a Bt corn made by Novartis that contained 40 times the amount of toxin in the Monsanto crop, was found to cause caterpillar mortality in the laboratory.
Dr Berenbaum said: "This is not the green light for all forms of genetically modified organisms but it does suggest there are ways to reduce the risk to non-target organisms at the very least by selecting particular GM varieties."