Date of this Version
1. NC-205 is a regional research committee supported by Land Grant Universities, USDA-CSREES and ARS. It is comprised of scientists from 20 states, Mexico and Canada who have conducted research on stalk-boring pests since 1954.
2. The Committee re-examined many of the assumptions upon which our previous scientific assessments were based. This update http://ent.agri.umn.edu/ecb/nc205doc.htm summarizes our scientific understanding and recommendations for resistance management of Bt corn. Our initial recommendations were published in North Central Regional Publication 602 during 1997. An electronic version of NCR-602 is located at http://www.extension.umn.edu/Documents/D/C/DC7055.html.
3. The Committee reaffirmed, as a premise, the importance of prolonging the durability of Bt corn technology. Bt corn provides more effective and consistent control of European corn borer than insecticides, with less cost and fewer logistical, health, or environmental concerns. Bt corn has insurance value by reducing risk of yield loss from European corn borer.
4. We believe that resistance management using the high-dose/refuge strategy is possible. Recent data based on samples from three localities support a key assumption that major resistance genes are rare. Survival of resistant heterozygotes is assumed to be low. Additional data are needed to confirm both assumptions.
5. Providing susceptible mates for resistant survivors in the Bt crop is a crucial component of resistance management. A refuge of 20-30% of the larval population of European corn borer should be protected from exposure to Bt toxin on each farm. Recent data on non-random mating and regional genetic structure of European corn borer, coupled with new theoretical models, suggest that a 20% refuge is the minimum needed for resistance management. A 30% refuge provides a hedge for uncertainty in biological and operational assumptions.
6. Economic analyses suggest corn growers can benefit from planting refuges. Under plausible biological, genetic and economic conditions, and a 10-20 year planning horizon, economic models indicate that farmers capture most, if not all, of the benefits of Bt technology by planting 20-30% refuge.
7. A refuge of 20-30% of the larval population of European corn borer can be achieved by planting 20-30% of the corn on a farm to unsprayed non-Bt corn. This area should increase to 40% if the refuge is sprayed with insecticides. The non-Bt corn refuge should be planted within each 320-acre area that has Bt corn, at a similar time and with similar maturity characteristics as the nearby Bt corn.
8. Possible biological threats to successful resistance management are declines in toxin concentration early in the growing season, interactions between minor and major resistance genes, non-random mating or inbreeding of resistant individuals, and the effects of Bt corn on natural enemies of pests and other non-target organisms.
9. Until additional data are obtained, we suggest that these recommendations for European corn borer be applied in areas where other stalk-boring pests of corn occur.
10. Growers are key partners in managing insect resistance to Bt corn. Dissemination of consistent information to growers is essential.