| Summary: | The corn earworm, <i>Helicoverpa zea</i> (Boddie), is a major pest of <i>Bacillus thuringiensis</i> (Bt) maize and cotton in the U.S. Reduced efficacy of Bt plants expressing Cry1 and Cry2 against <i>H. zea</i> has been reported in some areas of the U.S. In this study, we evaluated the occurrence and ear damage of <i>H. zea</i> on transgenic Bt maize expressing Cry proteins or a combination of Vip3A and Cry proteins in the field in Texas in 2018. We found that the occurrence of <i>H. zea</i> larvae and the viable kernel damage area on the ear were not different between non-Bt maize and Bt maize expressing Cry1A.105+Cry2Ab2 and Cry1Ab+Cry1F proteins. A total of 67.5% of the pyramided Bt maize expressing Cry1Ab+Cry1F+Vip3A was damaged by 2nd⁻4th instar larvae of <i>H. zea</i>. Diet bioassays showed that the resistance ratio against Vip3Aa51 for <i>H. zea</i> obtained from Cry1Ab+Cry1F+Vip3A maize was 20.4 compared to a field population collected from Cry1F+Cry1A.105+Cry2Ab2 maize. Leaf tissue bioassays showed that 7-day survivorship on WideStrike3 (Cry1F+Cry1Ac+Vip3A) cotton leaves was significantly higher for the <i>H. zea</i> population collected from Cry1Ab+Cry1F+Vip3A maize than for a Bt-susceptible laboratory population. The results generated from this study suggest that <i>H. zea</i> has evolved practical resistance to Cry1 and Cry2 proteins. Therefore, it is crucial to ensure the sustainable use of the Vip3A technology in Bt maize and cotton.
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