Effectiveness of Bt Cotton Towards Bollworms and Benefit of Supplemental Oversprays

Since the introduction of Bt cotton in the United States in 1996, management of the bollworm  has become much less problematic.  However, there are still incidents where unacceptable fruit injury is experienced and insecticidal oversprays are utilized to prevent yield loss.  There has been much speculation surrounding the reasons for control failures among Bt cotton technologies including Bt resistance or tolerance, inadequate expression of Bt toxins expression due to plant phenology or environmental stressors.  The objective of this project was to evaluate the efficacy of second and third generation Bt cotton at multiple locations within the Mid-South for efficacy towards bollworms and to determine if overspraying Bt cotton results in a reduction in damage and increased yields relative to non-Bt cotton. Additionally, we report diet incorporated and leaf tissue bioassays with Cry1Ac.