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ARS Home » Southeast Area » Stoneville, Mississippi » Southern Insect Management Research » Research » Publications at this Location » Publication #204587
Title: Genetic Variation for Resistance to Bacillus thuringiensis Toxins in Helicoverpa zea (Lepidoptera: Noctuidae) in Eastern North Carolina

Author
item Jackson, Ryan
item GOULD, F - NC STATE UNIVERSITY
item BRADLEY JR., J - NC STATE UNIVERSITY
item VAN DUYN, J - NC STATE UNIVERSITY

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2006
Publication Date: 10/1/2006
Citation: Jackson, R.E., Gould, F., Bradley Jr., J.R., Van Duyn, J.W. 2006. Genetic Variation for Resistance to Bacillus thuringiensis Toxins in Helicoverpa zea (Lepidoptera: Noctuidae) in Eastern North Carolina. Journal of Economic Entomology. 99:1790-1797

Interpretive Summary: Bollworm populations in North Carolina were evaluated to determine whether resistance to two proteins, Cry1Ac and Cry2Ab, that are produced in commercially available Bt cotton varieties had increased over a three-year period. Results from this study indicated that major genes conferring resistance to these proteins had not measurably increased during this period. However, there appeared to be minor genes that afforded an increased tolerance to these proteins. Information generated from this experiment is important in two aspects: 1) it let us know that either current Bt resistance management strategies were effective in delaying resistance development or that there was some fitness cost associated with major resistance genes, and 2) it suggested that future Bt resistance monitoring programs should not only focus on major resistance genes, but minor genes as well.

Technical Abstract: In order to evaluate resistance to Bacillus thuringiensis Berliner toxins, female bollworm moths, Helicoverpa zea (Boddie), were collected from four light trap locations in two eastern North Carolina counties from August-October during 2001 and 2002. Moths were allowed to oviposit, and upon hatch, 24 neonates from each female (F1 lines) were screened for survival and growth rate on each of three diets: non-Bt diet, diet containing 5.0 'g/ml Cry1Ac toxin, or diet containing 5.0 'g/ml Cry2Ab toxin. These screens were designed to identify non-recessive Bt resistance alleles present in field populations of bollworm. Out of 561 and 691 families screened with both Cry1Ac- and Cry2Ab-containing diets in 2001 and 2002, respectively, no F1 lines were identified that appeared to carry a gene conferring substantial resistance to either Cry1Ac or Cry2Ab. Adults from F1 lines with growth scores in the highest (R) and lowest (S) quartiles were mated in 4 combinations, RxR, SxR, RxS and SxS. Differences in growth rates of larvae from these crosses demonstrated that there is substantial quantitative genetic variation in eastern NC populations for resistance to both Cry1Ac and Cry2Ab toxins. These findings, in addition to results suggesting partially dominant inheritance of resistance to Cry1Ac and Cry2Ab, are critically important for determining appropriate resistance management strategies that impact the sustainability of transgenic cottons.