Resistance management of western corn rootworm (Coleoptera: Chrysomelidae) in transgenic Bt maize

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2024-05
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McCulloch, John
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Gassmann, Aaron
Hodgson, Erin
Abel, Craig
Bradbury, Steven
Owen, Michael
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Entomology
Abstract
Transgenic maize producing insecticidal toxins from the bacterium Bacillus thuringiensis (Bt) has been used to manage western corn rootworm, a major pest of maize, since 2003. However, this pest rapidly evolved resistance to Bt traits expressed in maize for rootworm management. This research examines several aspects of resistance management. A field study was used to quantify how larval density-dependent mortality of western corn rootworm in Bt and non-Bt maize impacts calculations of mortality imposed by Bt traits. A second field study was used to evaluate the use of a soil-applied insecticide with Bt maize to reduce feeding injury by western corn rootworm and delay resistance to Bt maize. Lastly, a computer model was used to examine the impact on expected time to resistance for maize producing two Bt traits when resistance to one of the traits was already elevated in the pest population, a scenario which reflects the timeline of resistance history of Bt maize for management of western corn rootworm. An unexpected but significant interaction was observed which caused higher proportions of individuals to die in Bt maize compared to non-Bt maize as initial egg density increased, which caused a significant positive correlation between mortality induced by Bt traits and egg density if not considered. The use of a soil-applied insecticide provided a short-term economic benefit when used with Bt maize in the limited case where a western corn rootworm population exhibited incomplete resistance to Bt maize. Computer simulations showed that expected time to resistance decreased for maize producing two Bt toxins as previous resistance to one of the toxins increased. These data increase our knowledge of western corn rootworm and will be useful to improve management for this pest and for other insect pests of current and future transgenic crops.
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