Enhancement of refuges for Helicoverpa armigera (Lepidoptera: Noctuidae) used in the resistance management plan for cotton (Gossypium hirsutum L.) containing Bollgard II® traits

Helicoverpa armigera (Hübner) egg densities were sampled across interfaces between cotton containing Bollgard II® traits and pigeonpea or unsprayed non-transgenic cotton refuges to determine the effectiveness of the refuge crops for Bollgard II® resistance management plans (RMPs) against H. armigera. Additionally, a commercially available moth-attraction technology (Magnet®) was included at interfaces with both refuge crops to determine whether the use of such an attractant technology enhances the effectiveness of the refuges. Where the refuge crop was unsprayed non-transgenic cotton, there was no consistent change in the egg-density profile across the interface, suggesting that the Helicoverpa moths were not detecting and responding to the transition from Bollgard II® to non-transgenic cotton. However wherever Magnet was applied, there was a consistent increase in egg density on or near the Magnet-treated cotton rows. This suggests that moth-attraction technology has potential to increase the efficiency of non-transgenic cotton refuges by increasing oviposition there so that the refuge produces more individuals unselected for Bt trait resistance. However, it is not yet known how best to deploy insect-attraction technology in non-transgenic cotton refuges. Pigeonpea was a very attractive refuge crop, with Helicoverpa egg densities an order of a magnitude higher than the adjacent Bollgard II® crop and with no spillover of this increased oviposition into cotton. Application of moth attractant to the edge of the pigeonpea refuge did not alter the egg-density profile across the crop interface, suggesting that the combination of moth-attraction technology with pigeonpea refuges would not increase the effectiveness of the refuge. These studies identify avenues for improving the effectiveness of refuge crops for the management of Bt resistance in H. armigera.