Fitness costs associated with Vip3Aa resistance on various hosts in Helicoverpa zea

Transgenic crops containing Bacillus thuringiensis (Bt) proteins are crucial for managing major agricultural pests such as the corn earworm, Helicoverpa zea (Boddie). The fitness of Bt resistant insects on refuge crops plays an important role in determining the rate of resistance development. Previous research has investigated the fitness costs of Cry1 and Cry2 resistance in H. zea, but limited information is available about the fitness costs associated with Vip3Aa resistance in this pest. Here, we evaluated fitness costs of Vip3Aa-resistant H. zea on three non-Bt hosts: meridic diet, corn ears, and cotton leaves.

On meridic diet, we detected recessive fitness costs resulting in lower survival and fecundity, and dominant fitness costs resulting in longer developmental time and reduced egg hatching rates. On corn ears, we observed recessive fitness costs resulting in lower pupal mass, and dominant fitness costs resulting in lower survival and fecundity, longer developmental time, and reduced egg hatching rates. On cotton leaves, we found recessive fitness costs resulting in lower female pupal mass, and dominant fitness costs resulting in lower adult survival and fecundity, and longer developmental time.

Significant differences in survivorship, developmental time, pupal mass, and reproduction among the Vip3A-resistant (RR), -susceptible (SS) and -heterozygous (R_♂S_♀ and R_♀S_♂) H. zea strains on the three hosts, revealed clear evidence of fitness costs associated with Vip3Aa resistance. These findings support the value of abundant non-Bt refuges in limiting the evolution of H. zea resistance to Vip3Aa in the field. © 2026 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.