BIOLOGY, ECOLOGY AND CONTROL OF WHITEFLIES
Location: Pest Management and Biocontrol Research
Title: Novel Pink Bollworm Resistance to the Bt Toxin:Cryl Ac: Effects on Mating, Oviposition, Larval Development, and Survival.
Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 28, 2008
Publication Date: May 22, 2009
Citation: Fabrick, J.A., Jech, L.J., Henneberry, T.J. 2009. Novel Pink Bollworm Resistance to the Bt Toxin:Cryl Ac: Effects on Mating, Oviposition, Larval Development, and Survival. 8pp. Journal of Insect Science. 9:24
Interpretive Summary: Protein toxins from the bacterium Bacillus thuringiensis (Bt) kill key agricultural insect pests and have been genetically engineered into crops. Cry1Ac is a toxin produced in Bt cotton and is effective for controlling pink bollworm, a major insect pest of cotton. Here we show that a pink bollworm strain (Bt4R) selected for 42 generations on Bt cotton can survive in artificial diet bioassays at discriminating concentrations of Cry1Ac, but remain susceptible to Bt cotton plants. We compared susceptibility to Cry1Ac, fecundity, egg viability, and mating of the Bt4R strain with an unselected Cry1Ac-susceptible pink bollworm strain. In contrast to resistant pink bollworm strains previously selected on Cry1Ac diet, inheritance of resistance in the Bt4R strain is not completely recessive and resistant individuals do not carry known mutations in cadherin genes found in all previous resistant strains selected on Cry1Ac-treated artificial diet. The combined results suggest a mechanism of resistance to Cry1Ac that is different from previously described cadherin mutations.
Bt cotton plants are genetically engineered to produce insecticidal toxins from the Bacillus thuringiensis (Bt) bacterium and target key lepidopteran pests. At least four strains of pink bollworm, Pectinophora gossypiella (Saunders), have been selected in the laboratory for resistance to insecticidal Cry1Ac toxin incorporated into artificial diet. In these strains, resistance to Cry1Ac and Bt cotton is linked to three cadherin alleles (r1, r2, and r3). We selected a pink bollworm strain for resistance to Bt cotton by feeding larvae for four days in each of 42 generations on bolls of ‘NuCOTN33B' expressing Cry1Ac toxin. Susceptibility to Cry1Ac, fecundity, egg viability, and mating of the Bt4R strain selected for Cry1Ac tolerance on cotton bolls compared with an unselected Cry1Ac-susceptible pink bollworm strain. Some larvae of the Bt4R strain survived on diet containing discriminating concentrations of Cry1Ac, but none survived on transgenic cotton bolls. In contrast to strains selected on Cry1Ac diet, some survival of progeny of reciprocal moth crosses of Bt4R resistant and Bt-susceptible strains occurred on Cry1Ac-treated diet. The Bt4R resistant strain does not have the r1, r2, or r3 mutant cadherin genes as do all previous strains of pink bollworm selected on Cry1Ac-treated artificial diet. The combined results suggest a mechanism of resistance to Cry1Ac that is different from previously described cadherin mutations.