Molecular genetic basis of lab- and field-selected Bt resistance in pink bollworm

Authors: Fabrick, Jeffrey; LI, XIANCHUN - University Of Arizona; CARRIERE, YVES - University Of Arizona; TABASHNIK, BRUCE - University Of Arizona

Submitted to: Insects
Publication Type: Review Article
Publication Acceptance Date: 2/3/2023
Publication Date: 2/17/2023
Citation: Fabrick, J.A., Li, X., Carriere, Y., Tabashnik, B. 2023. Molecular genetic basis of lab- and field-selected Bt resistance in pink bollworm. Insects. 14(2). Article 201. https://doi.org/10.3390/insects14020201.
DOI: https://doi.org/10.3390/insects14020201

Interpretive Summary: The pink bollworm, Pectinophora gossypiella, is one of the most damaging pests of cotton world-wide. Cotton has been genetically engineered to produce insect-killing proteins from the bacterium Bacillus thuringiensis (Bt) to control major lepidopteran pests including the pink bollworm. The Bt proteins in genetically engineered crops are not toxic to people, other vertebrates, or most beneficial insects. Advantages of Bt crops can include pest suppression, improved yields, increased farmer profits, and decreased use of conventional insecticides that benefits the environment and human health. However, these benefits are reduced when pests evolve resistance to Bt crops. The pink bollworm rapidly evolved resistance to Bt cotton in India, but not in China or the United States where this invasive pest was eradicated using Bt cotton, sterile moth releases, and other tactics. Here an ARS scientist from Maricopa, AZ and a collaborator compared the molecular genetic basis of pink bollworm resistance between lab-selected strains from the U.S. and China versus field-selected populations from India for two Bt proteins (Cry1Ac and Cry2Ab) produced in widely adopted Bt cotton. For each of two Bt proteins used widely in Bt cotton, the genetic basis of resistance is similar across countries and between resistance selected in the lab versus the field. The results suggest that lab selection can be useful for identifying genes likely to be important in field-evolved resistance to Bt crops and that differences in management practices among countries caused the different outcomes.

Technical Abstract: Transgenic crops producing insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) control some important insect pests. However, evolution of resistance by pests reduces the efficacy of Bt crops. Here we review resistance to Bt cotton in the pink bollworm, Pectinophora gossypiella, one of the world’s most damaging pests of cotton. Field outcomes with Bt cotton and pink bollworm during the past quarter century differ markedly among the world’s top three cotton-producing countries: practical resistance in India, sustained susceptibility in China, and eradication of this invasive lepidopteran pest from the United States achieved with Bt cotton and other tactics. We compared the molecular genetic basis of pink bollworm resistance between lab-selected strains from the U.S. and China versus field-selected populations from India for two Bt proteins (Cry1Ac and Cry2Ab) produced in widely adopted Bt cotton. Both lab- and field-selected resistance are associated with mutations affecting the cadherin protein PgCad1 for Cry1Ac and the ATP-binding cassette transporter protein PgABCA2 for Cry2Ab. The results imply lab selection is useful for identifying genes important in field-evolved resistance to Bt crops, but not necessarily the specific mutations in those genes. The results also suggest that differences in management practices, rather than genetic constraints, caused the strikingly different outcomes among countries.