Abundance and mortality of overwintering pupae of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) on the Darling Downs, Queensland, Australia

Abstract

Surveys were conducted between 1997 and 2001 to investigate the incidence of overwintering Helicoverpa spp. pupae under summer crop residues on the Darling Downs, Queensland. Only Helicoverpa armigera was represented in collections of overwintering pupae. The results indicated that late-season crops of cotton, sorghum, maize, soybean, mungbean and sunflower were equally likely to have overwintering pupae under them. In the absence of tillage practices, these crops had the potential to produce similar numbers of moths/ha in the spring. There were expected differences between years in the densities of overwintering pupae and the number of emerged moths/ha. Irrigated crops produced 2.5 times more moths/ha than dryland crops. Overall survival from autumn-formed pupae to emerged moths averaged 44%, with a higher proportion of pupae under maize surviving to produce moths than each of the other crops. Parasitoids killed 44.1% of pupae, with Heteropelma scaposum representing 83.3% of all parasitoids reared from pupae. Percentage parasitism levels were lower in irrigated crops (27.6%) compared with dryland crops (40.5%). Recent changes to Helicoverpa spp. management in cotton/grain-farming systems in south-eastern Queensland, including widespread adoption of Bt cotton, and use of more effective and more selective insecticides, could lead to lower densities of overwintering pupae under late summer crops.

Consumptive and non‐consumptive effects of wolf spiders on cotton bollworms

“…In temperate regions, H. armigera overwinter as pupae in the soil and then emerge as adults in the spring (Fitt, 1989). As part of the RMP, growers planting Bt cotton are required to undertake intensive post-harvest cultivation, referred to as 'pupae busting', to reduce survival of overwintering H. armigera pupae (Lloyd et al, 2008). Destruction of overwintering Bt-resistant pupae is a key component of the Resistance Management Plan (RMP) deployed by the Australian cotton industry to constrain the proliferation and spread of Bt-resistant H. armigera .…”

“…Minimum tillage involves the maintenance of permanent soil beds, with only occasional furrow delving to build up the ridges (NSW DPI, 1998), so it does not provide sufficient soil disturbance to substantially reduce survival of overwintering pupae (Duffield, 2004;Lloyd et al, 2008). However, the stable soil beds and complex vegetation present in minimum-tilled grounds may provide an in-crop refuge for predators, thereby enhancing the biodiversity and abundance of natural enemies of H. armigera.…”

“…In temperate regions, H. armigera overwinter as pupae in the soil and then emerge as adults in the spring (Fitt, 1989). Survival of overwintering H. armigera pupae in Bt cotton crops is an important issue for the cotton industry; overwintering pupae are the end result of 4-6 generations of selection in Bt cotton crops during the previous cotton season (Baker et al, 2011) and potentially convey genes for Bt resistance from one season to the next (Lloyd et al, 2008). Destruction of overwintering Bt-resistant pupae is a key component of the Resistance Management Plan (RMP) deployed by the Australian cotton industry to constrain the proliferation and spread of Bt-resistant H. armigera .…”

“…Destruction of overwintering Bt-resistant pupae is a key component of the Resistance Management Plan (RMP) deployed by the Australian cotton industry to constrain the proliferation and spread of Bt-resistant H. armigera . As part of the RMP, growers planting Bt cotton are required to undertake intensive post-harvest cultivation, referred to as 'pupae busting', to reduce survival of overwintering H. armigera pupae (Lloyd et al, 2008). To be effective, pupae busting requires full soil surface disturbance to a depth of 10 cm (Rourke, 2002).…”

Evolution, ecology and management of resistance in Helicoverpa spp. to Bt cotton in Australia

“…The components of the RMP include restricting the period within which cotton can be planted, controlling self-sown Bt-plants in non-Bt fields and vice versa, and banning the use of Bt sprays in refuges. Two further key elements of the RMP are the obligatory planting of refuge crops (Cerda and Wright, 2003) and cultivating the soil underneath Bt cotton fields during winter to increase the mortality of any diapausing pupae (Lloyd et al, 2008).…”