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Landscape-level variation in Bt crops predict Helicoverpa zea (Lepidoptera: Noctuidae) resistance in cotton agroecosystems.

BACKGROUND
Helicoverpa zea (Boddie) damage to Bt cotton and maize has increased due to widespread Bt resistance across the USA Cotton Belt. Our objective was to link Bt crop production patterns to cotton damage through a series of spatial and temporal surveys of commercial fields to understand how Bt crop production relates to greater than expected H. zea damage to Bt cotton. To do this, we assembled longitudinal cotton damage data that spanned the Bt adoption period, collected cotton damage data since Bt resistance has been detected, and estimated local population susceptibility using replicated on-farm studies that included all Bt pyramids marketed in cotton.


RESULTS
Significant year effects of H. zea damage frequency in commercial cotton were observed throughout the Bt adoption period, with a recent damage increase after the year 2012. Landscape-level Bt crop production intensity over time was positively associated with the risk of H. zea damage in two- and three-toxin pyramided Bt cotton. Helicoverpa zea damage also varied across Bt toxin types in spatially replicated on-farm studies.


CONCLUSIONS
Landscape-level predictors of H. zea damage in Bt cotton can be used to identify heightened Bt resistance risk areas and serves as a model to understand factors that drive pest resistance evolution to Bt toxins in the southeastern United States. These results provide a framework for more effective insect resistance management (IRM) strategies to be used in combination with conventional pest management practices that improve Bt trait durability while minimizing the environmental footprint of row crop agriculture. This article is protected by copyright. All rights reserved.