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ARS Home » Pacific West Area » Maricopa, Arizona » U.S. Arid Land Agricultural Research Center » Pest Management and Biocontrol Research » Research » Publications at this Location » Publication #198037
Title: High-level resistance to Bt toxin cryiac and cadherin genotype in pink bollworm

Author
item TABASHNIK, BRUCE - U OF A, TUCSON, AZ
item BIGGS, R - U OF A, TUCSON, AZ
item Fabrick, Jeffrey
item GASSMANN, A - U OF A, TUCSON, AZ
item DENNEHY, TIM - U OF A, TUCSON, AZ
item CARRIERE, Y - U OF A, TUCSON, AZ
item MORIN, S - UNIV OF JERUSALEM, ISRAEL

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2006
Publication Date: 12/1/2006
Citation: Tabashnik, B.E., Biggs, R.W., Fabrick, J.A., Gassmann, A.J., Dennehy, T.J., Carriere, Y., Morin, S. (2006). High-level resistance to Bt toxin cryiac and cadherin genotype in pink bollworm. Journal of Economic Entomology, 99(6):2125-2131

Interpretive Summary: Transgenic corn and cotton producing Bacillus thuringiensis (Bt) toxins that kill larvae of some key insect pests are grown on millions of hectares annually. Evolution of resistance to Bt toxins by insect pests could compromise the benefits of this technology. Resistance to the Bt toxin Cry1Ac is linked with three recessive cadherin alleles in laboratory-selected strains of pink bollworm, Pectinophora gossypiella, a major cotton pest. Here we show that a strain (MOV97-R) from the Mohave Valley of Arizona with a high frequency of cadherin resistance alleles could be further selected for survival at a high dose of Cry1Ac, indicating genetic variation in survival and yielding >4300-fold resistance relative to a susceptible strain. Interestingly, variation in cadherin genotype did not explain variation in survival at the high dose of Cry1Ac, implying that one or more additional loci affect survival at the high concentration. Although previous results show that survival in the presence of high Cry1Ac concentrations is not required for resistance to Bt cotton producing Cry1Ac, the gene or genes other than cadherin conferring increased survival at this high concentration may be important in the mode of action of Bt toxins.

Technical Abstract: Resistance to Bacillus thuringiensis (Bt) toxin Cry1Ac is linked with three recessive alleles of a cadherin gene in laboratory-selected strains of pink bollworm, Pectinophora gossypiella (Saunders), a major cotton pest. Here we analyzed a strain (MOV97-R) from the Mohave Valley of Arizona that had a high frequency of cadherin resistance alleles, a high frequency of resistance to 10 'g Cry1Ac per ml of diet, and an intermediate frequency of resistance to 1000 'g Cry1Ac per ml of diet. We selected two strains for increased resistance by exposing larvae from MOV97-R to wheat germ diet with 1000 'g Cry1Ac per ml of diet. In both selected strains, two to three rounds of selection increased survival at 1000 'g Cry1Ac per ml of diet to at least 76%, indicating genetic variation in survival at this high concentration and yielding >4300-fold resistance relative to a susceptible strain. Variation in cadherin genotype did not explain variation in survival at 1000 'g Cry1Ac per ml of diet, implying that one or more additional loci affect survival at this concentration. This conclusion was confirmed with results showing that when exposure to Cry1Ac stopped, survival at 1000 'g Cry1Ac per ml of diet dropped substantially, but survival at 10 'g Cry1Ac per ml of diet remained close to 100%. Although previous results show that survival at 1000 'g Cry1Ac per ml of diet is not required for resistance to Bt cotton producing Cry1Ac, the gene or genes other than cadherin conferring increased survival at this high concentration may be important in the mode of action of Bt toxins.