Modified female calling behaviour in Cry1Ac-resistant Helicoverpa armigera (Lepidoptera: Noctuidae)

BACKGROUND: The resistance risk in Helicoverpa armigera (Hubner) to transgenic cotton that expresses Cry1Ac from Bacillus thuringiensis (Bt) has raised concerns about the sustainable deployment of Bt cotton. Mating behaviour between resistant and susceptible individuals is an important factor that affects resistance evolution of the insect. The female calling behaviours of the Cry1Ac-resistant strain and its susceptible control were compared in the laboratory to understand the difference in mating biology. RESULTS: The proportion of females of the resistant strain calling was significantly reduced by 14%, and the age of the calling peak was delayed by 1 night compared with that of the susceptible strain. During the scotophase, females of the resistant strain started calling more than 100 min later on nights 3 to 7, and spent 30–100 min less time on nights 2 to 7 than the susceptible females. The onset time of calling advanced and the time spent calling increased as a function of age in both susceptible and resistant strains. CONCLUSION: These results indicate that there is a fitness cost in terms of the female calling behaviour of the resistant strain. The lower proportion of females of the resistant strain showing calling behaviour could reduce the mating frequency of the resistant strain. The delayed onset time of calling in the resistant strain could reduce its mating time, and a reduction in the time spent calling could reduce the attractiveness of resistant females; this could also reduce the mating frequency of the resistant strain. Copyright © 2009 Society of Chemical Industry