Abundance of overwintering pupae and the spring generation of Helicoverpa spp. (Lepidoptera: Noctuidae) in northern New South Wales, Australia: implications for pest management

Helicoverpa armigera (Hubner) and H. punctigera (Wallengren) are major pests of cotton and other field crops in Australia. We measured the abundance, species composition, and survival of overwintering pupal populations under residues of autumn crops over two seasons (1987 and 1988) in the Namoi-Gwydir region, Australia. In 1987, cotton supported the highest densities of pupae with an estimated population of 556 million individuals, while 5 million in total were found under residues of sunflower, sorghum, and grain legumes. In 1988, the population of pupae under cotton (24 million) was only 5% of that in 1987, and more were found under sunflower residues (11 million). Levels of parasitism and other mortality were lower in pupae from under cotton than other crops, and a high proportion of pupae (40-50%) survived to emergence. Virtually all overwintering pupae located in the study area have been H. armigera. The regular spring reappearance of H. punctigera in the Namoi-Gwydir area, and possibly other eastern Australian cropping areas, must therefore derive largely from immigrants produced elsewhere. For H. armigera, the phenology of adult appearance in traps and emergence from diapause of local overwintering pupae suggests that spring populations consist of moths from local overwintering populations and from immigrant origin. This hypothesis is consistent with patterns of pyrethroid resistance measured in overwintering populations and during the spring of both seasons