|May Iii, Oscar|
Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/31/1996
Publication Date: N/A
Interpretive Summary: Reduction of pesticide use in cotton production is important to safeguard the environment and reduce production costs to growers. In southeastern USA cotton production where the boll weevil has been eradicated, the most damaging economic pest of cotton is the bollworm/budworm complex. These insects yearly cause yield-loss and reduce grower profits. An alternative to chemical control is the development of cultivars with genetic resistance to bollworm/budworm. Monsanto Company has genetically engineered cotton germplasm with a gene known as Bt that generally confers good resistance to the bollworm/budworm. This research documents additional efficacy trials and Bt resistance management efforts. This study found that larvae moved from non-Bt plants to Bt plants when grown in a 90:10 seed mix of genetically engineered to non-engineered plots. Therefore, bollworm/budworm resistance to the Bt gene management by the use of seed mixes in commercial production deserves additional study prior to releasing this technology to growers.
Technical Abstract: A field study was conducted to compare the relative densities, distribution patterns, and economic impact of bollworms (Helicoverpa zea Boddie) and budworms (Heliothis virescens F.) in Monsanto's transgenic cotton BT01DP' expressing the delta-endotoxin from the bacterium Bacillus thuringiensis subsp. kurstaki (Berliner)(Bt), a 90:10 Bt:non-Bt seed mix, and nontransgenic Coker 312' cotton. These treatments received no applications of insecticides for control of lepidopteran insects. The bollworm was the predominant species, comprising approximately 95% of the bollworm/budworm complex. Examination of ten consecutive plants in each of the two center rows of each plot revealed that 16.7% of plants in the 90:10 Bt:non-Bt plots infested with third-instar and larger larvae was significantly greater than the expected 9.5%. Similarly, the 9.2% of plants in the 90:10 plots infested with fourth-instar and larger larvae was significantly greater than the expected 4.9%. These higher than expected percentages of plants infested with large larvae in the 90:10 Bt:non-Bt plots indicated that movement of larvae from non-Bt to Bt plants occurred. Results indicated that movement of bollworm larvae to Bt plants may result in a significant increase in damage and reduced yield in mixed stands of Bt and non-Bt plants. Additional studies are needed to determine the relationships that exist among seed mix ratios, population densities of bollworms/ budworms, injury, and yield reductions.