When it comes to combating the European corn borer, farmers in Northeastern and Mid-Atlantic states should not count on any "help" from plants outside the corn field. To slow the development of resistance, farmers should carefully follow the EPA guidelines for planting refuges-the areas surrounding their biotech-corn fields-a study from the latest issue of Environmental Entomology confirms. The journal is published by the Entomological Society of America (ESA).

The genetically engineered corn, known as Bt corn, was developed to combat the European corn borer, a major crop pest that causes $1 billion in annual damage and control costs in the United States. Bt-corn hybrids contain a gene from the bacterium Bacillus thuringiensis, or Bt, that produces a toxin to kill European corn borers, but widespread use of this corn can lead to these insect pests developing resistance to the toxin.

To manage the resistance problem, EPA mandates that a minimum of 20 percent of each Bt-corn field be planted with genetically unaltered corn to serve as a "refuge" where European corn borers can grow without being exposed to the Bt toxin. These unexposed pests can then mate with any Bt-resistant survivors emerging from the corn, thus prolonging the pest population's susceptibility to the toxin.

It has been speculated that any type of genetically unaltered plants could serve as refuge plantings so long as they are the European corn borers' natural hosts, which happens to be over 200 plants including crops and weeds. However, ESA member John Losey, an entomologist from Cornell University and lead author of the study, found the pests favored corn over other plants, including weeds and other crops. During the 1998 and 1999 growing seasons, Losey-along with ESA members and entomologists Dennis Calvin of Pennsylvania State University, Maureen Carter of Cornell, and Charles Mason of the University of Delaware-examined the number of European corn borer eggs and larvae in two cornfield refuges in New York and Pennsylvania.

To reflect cornfields specific to the geographical area, the refuges consisted of two plots of corn, one planted early and the other planted late in the growing season, as well as soybeans, potato, oats, and weeds. The latter were known host plants for the corn borers that are widely distributed throughout the geographical area and included barnyardgrass, common ragweed, giant foxtail, lambsquarter, Pennsylvania smartweed, and redroot pigweed. As part of resistance management, no pesticides against European corn borer were used in the refuges.

In New York, Losey and colleagues found corn borer eggs only on corn, and in Pennsylvania only on corn, lambsquarter, and pigweed. The researchers also found in both sites more larvae on corn than any other plant. In comparing early- and late-planted corn, they found more larvae on the early corn. "We found very little evidence to suggest that a substantial proportion of European corn borer larvae develop to adults on plants other than corn," Losey said. "The pests' preference to corn may be at least partly due to the failure of non-corn host plants to provide all the requirements for European corn borer survival and development," he added.

Losey and colleagues also conducted a laboratory study to compare corn and common weeds as host plants of the insect pests. "We found that corn and ragweed were the two favorite hosts of corn borer larvae in the lab, at least two times more favored than the other plants," Losey said. The findings confirmed those of the field study.

Results from the study suggest that the size of refuges should not be decreased. "Our evidence does not support a recommendation of reduced refuge planting in the Northeast and Mid-Atlantic," Losey said.

Beginning August 16, the complete study can be accessed on the Web for free via http://www.entsoc.org/pubs/.

** NOTICE: In accordance with Title 17 U.S.C. Section 107, this material is distributed for research and educational purposes only. **