National Cotton Council

National Cotton Council Reaffirms That Bt Cotton Resistance Management For Pink Bollworm Is Sound

The National Cotton Council (NCC) today said it remains convinced that current resistance management strategies for pink bollworm -- including the use of refugia -- are appropriate and reaffirmed its commitment to preserving the effectiveness of Bt cotton.

Bt cotton contains a gene transferred from the bacterium Bt (Bacillus thuringiensis) that lets plants produce a safe, natural insecticide. When pink bollworm and certain other caterpillar pests of cotton feed on these plants, they die.

Dr. Frank Carter, NCC's manager, pest management, said there has been no demonstrated resistance to Bt in pink bollworm populations in the field. He said cotton growers recognize the threat of resistance and currently set aside a portion of their crop in non-genetically modified varieties (refugia) to ensure that the Bt product maintains its effectiveness. This resistance management strategy is based on a collaboration among scientists from leading universities and the USDA's Agricultural Research Service, and has been approved by the U.S. Environmental Protection Agency.

The NCC's affirmation of Bt and the use of refuges comes after a recent University of Arizona laboratory study, summarized in the journal Nature (Aug. 5, 1999) suggests that resistant pink bollworms develop more slowly on Bt cotton.

"This (Arizona) laboratory study infers that delayed development would somehow interrupt the randomness of mating of resistant moths surviving the Bt cotton with the susceptible ones in the non-Bt cotton refugia," Carter said. "While NCC supports research that contributes to our knowledge base on pink bollworm, these findings must be studied more thoroughly under field conditions. It is premature to conclude that deployment of refuges is not an effective resistance management strategy."

Carter, an entomologist, said, "in a field situation, the cotton plants, along with tens of thousands of insects and plants are on different development schedules. Pink bollworms moths emerge, mate and reproduce every day from early spring to mid-summer, consequently, there will be ready supply of susceptible moths present if any resistant moths emerge. This supports the position that the refuge system is a valid strategy for resistance management in pink bollworm.

"This information (Arizona study) is encouraging in that this is further evidence that Bt resistance is recessively inherited and secondly, that the refuge strategy will work by countering delayed development of resistant moths by providing a continuous daily supply of moths to mate with those surviving the Bt cotton. This is good news."

Chuck Youngker, chairman of the Arizona Cotton Growers Association, said, "Bt cotton is a very important technology for our members. We believe in insect resistance management, and we're committed to doing whatever it takes to continue receiving the benefits it provides."

EDITOR'S ADVISORY: Additional expert comments:

Dr. John Foster is a professor of entomology at the University of Nebraska and a member of a national committee (NC205) working to develop refuge management policy. Media may call Dr. Foster at 402-472-8686.

"There is nothing new here. Entomologists working on insect resistance management issues have long known about developmental asynchrony and have considered it in proposing defenses against resistance. Asynchrony is in every entomology textbook. I have no problem with the research being done, but it's a little surprising it is being released at this time and with the implication that it has uncovered something new and significant in regards to resistance management.

"I also take exception to the statement that these laboratory findings contradict an important assumption of the refuge strategy. Nothing is contradicted until it is proven in the field. A laboratory experiment, where populations are artificially controlled does not replicate a field environment.

"In the field, all insects do not emerge at the same time and they don't all develop at the same rate. There is considerable overlap in generations. Therefore, there will be populations of susceptible insects to mate with any resistant insects. I think this study has very little relevance to current strategies for insect resistance management."

Dr. John Benedict, professor emeritus at Texas A&M University, has more than 24 years of experience as a research entomologist in cotton.

"I believe the laboratory findings are insignificant relative to the strength or value of the refuge strategy. Furthermore, the findings are insignificant relative to the societal value of Bt technology. When you consider the perspective of sustainability, integrated pest management, reduction in insecticide applications and overall societal value, Bt technology gets all A's. That should not be lost in the narrow focus on resistance management."

Dr. Theo Watson studied pink bollworm populations for more than 30 years before retiring in 1995 from the University of Arizona. Media may call Dr. Watson at 520-327-7969.

"The results of a laboratory study are not an indication of what will happen in a natural setting. The pink bollworm is asynchronous to begin with. In other words, from early spring to mid-summer, new moths are appearing on a daily basis and producing offspring. The fact that exposed larvae take 5.7 days longer to mature is meaningless in a natural setting because staggered populations develop under normal circumstances. Therefore, there will be numerous mates in the refuge for any resistant moths that might survive exposure to Bt cotton. And, because the resistance gene is recessive, as the Nature article points out, the offspring of the pairing will be susceptible to Bt. I do not see this laboratory result as anything to be concerned about in a natural setting."

Another contact is:

Dr. Peter Ellsworth
IPM Specialist
University of Arizona
Maricopa, AZ
520-568-2273

CONTACT: T. Cotton Nelson or Frank Carter of National Cotton Council, 901-274-9030