Diapause, migration and pyrethroid‐resistance dynamics in the cotton bollworm, <i>HeIicoverpa armigera</i> (Lepidoptera: Noctuidae)

Abstract

Abstract. A diapause induction and duration experiment was conducted in the laboratory on Indian Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) where 79% of individuals had extended pupal periods. At 22°C and 26°C respectively, 57% and 100% of the pupae had emerged 145 days after pupation. A mathematical model was developed to investigate the interactions between diapause, migration and pyrethroid resistance frequency development in both eastern Australia and Andhra Pradesh, India. The effect of diapause was different in the Australian and Indian cases, providing a mechanism to conserve resistance and susceptibility respectively. For Australia, the model simulated discriminating dose data reasonably well and showed that resistance frequencies could rise prior to the pyrethroid window without invoking cross‐resistance to non‐pyrethroid insecticides applied to cotton. The saw‐toothed seasonal cycle of resistance development could be simulated in the Indian case without hypothesizing the existence of susceptible migrants. The implications of‘refugia’populations for H.armigera insecticide resistance management programmes are discussed.