Submitted to: Crop Protection Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2007
Publication Date: 3/20/2008
Citation: Huang, F., Leonard, W.R., Reagan, T., Stout, M., Akbar, W., Moore, S., Cook, D., Lee, D., White, W.H., Yue, B., Parker, R., Chilcutt, C., Biles, S. 2008. Geographical susceptibility of Louisiana and Texas populations of sugarcane borer, Diatraea saccharalis (F.) (Lepidopetera: Crambidae) to Bacillus thuringiensis Cry1Ab protein. Crop Protection. 27:799-806. Interpretive Summary: Preventing damage by larvae of the sugarcane borer moth with insecticides represents a major cost input by Louisiana and Texas corn, rice, sorghum, and sugarcane farmers. The use of these insecticides also represents an important environmental concern as well. Growing crop varieties with resistance to this pest is an important alternative to the use of insecticides. This resistance can be either natural to the crop or come from genes introduced from another organism that produce a toxin lethal to this larvae. Genes isolated from a bacterium that produce such a toxin has been introduced into several important crops; however, only in corn and cotton has this technology been used on a commercial basis. Even though the plant is producing the toxin, it is still considered an insecticide and therefore is subject to being rendered non-toxic by strains of insects that have become resistant to the toxin. In this study, researchers from Louisiana and Texas studied populations of sugarcane borer that have been exposed to transformed corn for eight years. If evidence were found that suggested that resistance to the toxin was developing then concerns would arise that this form of resistance was breaking down. This finding would obviously have a profound impact on the future of this technology. Results from laboratory evaluations, however, indicate that resistance is not developing to the toxin and for the immediate future the deployment of these genes in corn is safe. These findings are of great importance to commercial seed producers as they can continue to release corn varieties with the toxin and they can also continue the research and deployment of these genes into other agricultural crops. Farmers will continue to enjoy the costs savings by not having to make repeated applications of expensive insecticides while the non-farming community will continue to benefit from not having these chemicals enter the environment.
Technical Abstract: The susceptibility of 18 field populations of the sugarcane borer, Diatraea saccharalis (F.) to two sources of Bacillus thuringiensis Cry1Ab protein was determined by laboratory bioassays. Fifteen of the 18 field populations were collected from seven locations across Louisiana and the other 3 populations were sampled from the Gulf Coast of Texas during 2004-2006. Neonates of D. saccharalis were exposed to a meridic diet treated with selected concentrations of Cry1Ab protein. Larval mortality was measured at 7 days after inoculation. Statistically significant differences in median lethal concentrations (LC50s) were detected among insect populations from different geographical locations, but the field populations remained as susceptible as a laboratory strain of D. saccharalis that had been maintained in the laboratory for >20 years without exposure to any chemical insecticides or Bt toxins. The LC50s of Cry1Ab protein, which was extracted from DKC69-70 Bt corn hybrid, ranged from 0.03 to 0.32 ug/g for the seven field populations collected during 2004. The LC50s values based on bioassays with purified, trypsin-activated Cry1Ab protein from a recombinant Escherichia coli culture were 0.03 to 0.17 ug/g for the 11 field populations collected during 2005-2006. Small changes in Cry1Ab susceptibility were detected among crop years, years of sampling, or locations. All field-collected insect populations, except one, exhibited lower LC50s values than the laboratory strain. The results of this study suggest that field D. saccharalis remain generally susceptible to the Cry1Ab protein after eight years use of transgenic Bt corn in Louisiana and the Gulf Coast area of Texas.