Best management practices to delay the evolution of Bt resistance in lepidopteran pests without high susceptibility to Bt toxins in North America

Authors: REISIG, D. D. - North Carolina State University; DIFONZO, C. - Michigan State University; DIVELY, G. - University Of Maryland; FARHAN, Y. - University Of Guelph; GORE, J. - Mississippi State University; SMITH, J. - University Of Guelph

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/23/2021
Publication Date: 12/18/2021
Citation: Reisig, D., Difonzo, C., Dively, G., Farhan, Y., Gore, J., Smith, J. 2021. Best management practices to delay the evolution of Bt resistance in lepidopteran pests without high susceptibility to Bt toxins in North America. Journal of Economic Entomology. 115:10-25. https://doi.org/10.1093/jee/toab247.
DOI: https://doi.org/10.1093/jee/toab247

Interpretive Summary: Genetically modified crops expressing insecticidal proteins from the soil bacterium, Bacillus thuringiensis Berliner (Bt), are planted on 82% of the corn and 88% of the cotton acres in the United States and 88% of the corn acres in Canada. As part of the registration package for Bt crops in the U.S. and Canada, regulatory agencies require an insect resistance management (IRM) plan for target pest species. Canadian and United States (US) insect resistance management (IRM) programs for lepidopteran pests in Bacillus thuriengiensis (Bt)-expressing crops are optimally designed for European corn borer in corn and tobacco budworm in cotton. Although Bt corn and cotton express a high dose for these pests, Bt corn and Bt cotton do not express high doses for many other target pests. Western bean cutworm and bollworm are two such non-high dose pests which may develop resistance if IRM plans are not followed. IRM practices to delay Bt resistance that are designed for these two ecologically challenging and important pests should apply to species that are more susceptible to Bt toxins. The purpose of this article is to propose five best management practices to delay the evolution of Bt resistance in lepidopteran pests with low susceptibility to Bt toxins in Canada and the US: 1) better understand resistance potential before commercialization, 2) strengthen IRM based on regional pest pressure by restricting Bt usage where it is of little benefit, 3) require and incentivize planting of structured corn refuge everywhere for single toxin cultivars and in the southern US for pyramids, 4) integrate field and laboratory resistance monitoring programs, and 5) effectively use unexpected injury thresholds.

Technical Abstract: Canadian and United States (US) insect resistance management (IRM) programs for lepidopteran pests in Bacillus thuriengiensis (Bt)-expressing crops are optimally designed for Ostrinia nubilalis Hübner in corn (Zea mays L.) and Chloridea virescens Fabricius in cotton (Gossypium hirsutum L.). Both Bt corn and cotton express a high dose for these pests; however, there are many other target pests for which Bt crops do not express high doses (commonly referred to as nonhigh dose pests). Two important lepidopteran nonhigh dose (low susceptibility) pests are Helicoverpa zea Boddie (Lepidoptera: Noctuidae) and Striacosta albicosta Smith (Lepidoptera: Noctuidae). We highlight both pests as cautionary examples of exposure to nonhigh dose levels of Bt toxins when the IRM plan was not followed. Moreover, IRM practices to delay Bt resistance that are designed for these two ecologically challenging and important pests should apply to species that are more susceptible to Bt toxins. The purpose of this article is to propose five best management practices to delay the evolution of Bt resistance in lepidopteran pests with low susceptibility to Bt toxins in Canada and the US: 1) better understand resistance potential before commercialization, 2) strengthen IRM based on regional pest pressure by restricting Bt usage where it is of little benefit, 3) require and incentivize planting of structured corn refuge everywhere for single toxin cultivars and in the southern US for pyramids, 4) integrate field and laboratory resistance monitoring programs, and 5) effectively use unexpected injury thresholds.