Opponents of genetically engineered foods have often cited a laboratory study suggesting that the population of Monarch butterflies would be seriously damaged if they consumed pollen from corn plants that produced the insecticidal Bt protein. Anti-biotechnology activists suggest that other species of beneficial or harmless insects would suffer as well. However, a new study published in the June 6 issue of the Proceedings of the National Academy of Science makes this gloomy forecast seem unlikely.
Researchers from the University of Illinois in Urbana performed a field experiment to test whether, under natural conditions, pollen from corn producing the Bt protein would harm larvae of the black swallowtail butterfly. When the gene for Bt, originally produced by the bacterium Bacillus thuringiensis, is transferred into corn plants by genetic engineering techniques, the corn begins produces this protein and it can be found in the corn pollen.
The black swallowtail butterfly is found widely throughout the eastern United States. Its larvae feed on only a few weed species, which typically grow in pastures, along roadsides and along the edges of cultivated fields. Thus, wind-blown pollen from genetically engineered corn could well be found on these weeds and eaten by black swallowtail butterfly larvae.
To investigate the effects of Bt pollen in the wild, the researchers placed potted host weed plants at different distances from fields of Bt corn. Ten black swallowtail larvae were placed on each plant, and their survival and condition were monitored for seven days. In addition, the researchers measured the amount of windblown pollen that was dispersed around the target plants.
The researchers found that neither the survival of the larvae nor their weight (an index of their condition) was affected by either the distance from the cornfield or by the amount of pollen that fell on their plants. Thus, the investigators concluded that although many of the larvae did die, there was “no evidence that pollen from corn contributed to that mortality.” In fact, the study authors indicated that other predatory insects were eating the larvae.
In addition to testing the Bt corn pollen under natural field conditions, the study authors also exposed black swallowtail larvae to varying amounts of Bt pollen in the laboratory. Again, they found that the pollen did not increase the mortality of the larvae compared to larvae exposed to pollen from non-engineered corn. Indeed, even when the larvae were exposed to a pollen concentration 40 times greater than they had encountered in the field, they were not affected.
The authors concluded that the use of genetically engineered crops, such as Bt corn, could be useful in reducing both the amount and environmental effects of chemical pesticides. They noted that such pesticides are more likely to affect non-targeted species of insects than would be true of genetically engineered crops.
Dr. Alan McHughen, professor at the University of Saskatchewan, and a molecular biologist, commented, “The data and evidence presented in this paper should effectively silence those critics who chose to negatively interpret the lab-based Monarch butterfly study from last year.
“This paper,” he continued, “shows that swallowtail butterflies, relatives of the Monarchs, suffered no undue harm in field situations when exposed to genetically modified corn pollen containing the Bt gene and protein.”