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October 26, 2018 | Patti Mulligan

When bollworm (Helicoverpa zea) attacks, cotton that is engineered to produce insecticidal toxins commonly called “Bt” (left) fends off the pest, while non-Bt cotton (right) is targeted and damaged. Pests such as H. zea can develop resistance to the toxins in Bt crops, however, and planting non-Bt crops nearby helps to slow evolutionary selection pressure that would lead to the development of resistance in the pest population. Planting such non-Bt “refuges” is an important, but underused, method for insecticide resistance management. (via Entomology Today; Photo credit: Dominic Reisig, Ph.D.)

By: DOMINIC REISIG, October 23, 2018

Bt crops—those genetically engineered to produce an insecticidal toxin from the bacterium Bacillus thuringiensis—are special due to their benefits: reducing foliar insecticide applications, which increase populations of beneficial insects and minimize environmental harm; reducing pest populations throughout the landscape; and preserving yield, to name a few. Therefore, preventing resistance to Bt crops is important and is usually formalized in a set of Insecticide Resistance Management (IRM) practices. Because bollworm (Helicoverpa zea,also commonly known as corn earworm and tomato fruitworm) is now resistant to two Bt toxin families (Cry1A and Cry2A) in cotton, IRM practices may have to change to slow resistance to other Bt toxins.

Although bollworm field resistance to single-toxin Bt has been known for many years, cotton farmers are now experiencing problems in the field due to resistance, spraying more insecticides for bollworm in two-Bt-toxin cotton. However, the implications of this resistance for IRM are bigger than just an increase in foliar insecticide sprays. In a forum article published in Environmental Entomology this month, cotton industry researcher Ryan Kurtz and I sought to detail many of these implications for the U.S. production system from our field-based perspective, listing current challenges and providing suggestions to meet those challenges.

Continue reading at Entomology Today

Related Publication

Dominic D Reisig, Ryan Kurtz; Bt Resistance Implications for Helicoverpa zea (Lepidoptera: Noctuidae) Insecticide Resistance Management in the United StatesEnvironmental Entomology, nvy142, https://doi.org/10.1093/ee/nvy142

Abstract
Both maize and cotton genetically engineered to express Bt toxins are widely planted and important pest management tools in the United States. Recently, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) has developed resistance to two toxin Bt maize and cotton (Cry1A and Cry2A). Hence, growers are transitioning to three toxin Bt cotton and maize that express both Cry toxins and the Vip3Aa toxin. H. zea susceptibility to Vip3Aa is threatened by 1) a lack of availability of non-Bt refuge crop hosts, including a 1–5% annual decline in the number of non-Bt maize hybrids being marketed; 2) the ineffectiveness of three toxin cultivars to function as pyramids in some regions, with resistance to two out of three toxins in the pyramid; and 3) the lack of a high dose Vip3Aa event in cotton and maize. We propose that data should be collected on current Cry-resistant H. zea in the field to inform future Bt resistance models and that the deployment of Bt toxins and non-Bt refuge crops should be adjusted to favor susceptibility of H. zea to Bt toxins such as Vip3Aa. Finally, maize growers should be incentivized to plant non-Bt structured refuge and have access to hybrids with high-yielding genetic potential at a reasonable price.
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