Are the goals of Bt resistance monitoring acceptable? Experiences with Helicoverpa zea in the southern US

Diet incorporated concentration-mortality bioassays have been used for Bt resistance monitoring of all pests since the introduction on Bt cotton in 1996. The goal of this monitoring program has been to detect individuals carrying a single gene that confers high levels of resistance to the target Bt protein. Based on field observations, it appears that subtle changes have occurred in H. zea populations across the southern U.S. that are not easily detected with laboratory bioassays. These changes appear to be transient and fluctuate from year to year and location to location. Experiences with field control of H. zea with Bt crops will be discussed.