Seed blends of pyramided Cry/Vip maize reduce Helicoverpa zea populations from refuge ears

Abstract

The Vip3A, a vegetative Bacillus thuringiensis (Bt) gene, has been introduced into many Cry maize and cotton varieties that can manage the recently occurred Cry1/Cry2 resistance in Noctuidae pests including Helicoverpa zea (Boddie) in the USA. A seed blend refuge has been used for providing susceptible insect populations for Bt maize resistance management. Four field trials were deployed in this study to investigate the effects of Bt protein contamination due to gene flow in seed blend refuges of Viptera maize containing Cry1Ab and Vip3Aa20 genes with 0–30% refuges on the survival, development, and reproduction of the parental and F1 generations of H. zea. Viptera maize is highly effective against H. zea and likely expresses a ‘high dose’ for the insect. Compared to the survival on the structured refuge, seed blends reduced approximately 70% of the pupal and adult productions from refuge ears, and the reductions were not related to the refuge percentage. Pupae from the seed blend refuge weighed 22.1% less than those from the structured refuge, but the body mass reduction did not significantly affect the reproduction per female. All field populations were highly resistant to Cry1Ab, but susceptible to Vip3Aa20. Fitness of the F1 generations from the structured and seed blend refuges in diet rearing was generally similar. Data generated from the study can be used in simulation modeling to evaluate the feasibility of seed blends for resistance management.