Field‐evolved resistance by western corn rootworm to Cry34/35Ab1 and other Bacillus thuringiensis traits in transgenic maize

Abstract

BACKGROUND Transgenic crops producing insecticidal toxins from the bacterium Bacillus thuringiensis (Bt) are widely planted to manage agricultural insect pests. However, widespread adoption of Bt crops has led to the evolution of Bt resistance. The western corn rootworm, Diabrotica virgifera virgifera, is among the most serious pests of maize in the midwestern United States and is currently managed with Bt maize. To date, there is evidence of field‐evolved resistance to all Bt toxins used to manage this pest. While western corn rootworm resistance to Cry3Bb1, and the closely related mCry3A and eCry3.1Ab traits, is widely distributed within the Midwest, fewer cases of Cry34/35Ab1 resistance have been observed, and planting of Cry34/35Ab1 maize is one of the methods used to manage Cry3‐resistant rootworm. RESULTS We found that fields with high levels of root injury to Cry34/35Ab1 maize by western corn rootworm were associated with Cry34/35Ab1‐resistant western corn rootworm. Additionally, a population not associated with high levels of root injury was found to be resistant to Cry34/35Ab1. In all cases, populations that were resistant to Cry34/35Ab1 also were resistant to Cry3 traits. CONCLUSIONS Western corn rootworm resistance to Cry34/35Ab1 has continued to persist in the agricultural landscape and has likely increased. The presence of rootworm populations with resistance to all available Bt traits threatens the utility of current and future transgenic technologies to manage this pest. Decreased reliance on Cry34/35Ab1 and better use of integrated pest management will be essential to preserve Bt susceptibility in western corn rootworm. © 2019 Society of Chemical Industry

Functional validation of DvABCB1 as a receptor of Cry3 toxins in western corn rootworm, Diabrotica virgifera virgifera

“…Cases of field resistance to Cry3Bb1 and cross-resistance to mCry3A and eCry3.1Ab have been reported in WCR 15,16 . Lab bioassays confirmed cross-resistance among Cry3Bb1, mCry3Aa, and eCry3.1Ab, but not to the binary Bt toxin Cry34/35Ab1 11,17,18 . These cases of field resistance coupled with demonstrated cross-resistance amongst the Cry3-based traits threatens the usefulness of these traits to growers in the US.…”

Comparing Populations of Western Corn Rootworm (Coleoptera: Chrysomelidae) in Regions With and Without a History of Injury to Cry3 Corn

“…Soil insecticide can reduce adult emergence, which can lead to lower population numbers overall ( Shrestha et al 2018a ). While field-evolved resistance to Cry34/35Ab1 does exist, resistant populations were relatively rare in Iowa at the time of this study, so this Bt toxin was likely an effective method of managing rootworm ( Gassmann et al 2016 , 2020 ). Thus, differences in management can explain why rootworm abundance and root injury did not differ between county types, even though a higher rootworm prevalence would be expected in counties where fields had previously experienced injury to corn.…”

“…Across the entire study, 53 and 95% of fields in non-problem and problem counties, respectively, used a corn hybrid expressing Cry34/35Ab1, either singly or as a pyramid with a Cry3 protein ( Table 4 ). While it is evidently providing an economic benefit to farmers, such widespread use of this trait is selecting for resistance to Cry34/35Ab1, cases of which have already been documented ( Gassmann et al 2016 , 2020 ).…”

“…There are currently four traits available for rootworm management either singly or as a pyramid of two toxins (Cry3Bb1, mCry3A, Cry34/35Ab1, and eCry3.1Ab) ( Gassmann 2016 ). However, field-evolved resistance by western corn rootworm has been documented for all four toxins ( Gassmann et al 2011 , 2014 , 2020 ; Jakka et al 2016 ).…”

Making sense of Integrated Pest Management (IPM) in the light of evolution

“…However, resistance may not only evolve in response to synthetic pesticides but to any control measure. For example, pest resistance has developed to insecticides expressed by Bacillus thuringiensis (Bt) genes in transgenic “Bt crops” (Gassmann, Shrestha, Kropf, St Clair, & Brenizer, 2019; Janmaat & Myers, 2003) and to biological control (Tomasetto, Tylianakis, Reale, Wratten, & Goldson, 2017). Similarly, pests would naturally be under selective pressure to adapt to resistance mechanisms bestowed by incorporating genes from CWRs into crop plants.…”