Mortality of Helicoverpa in Bollgard II® cotton fields and implications for Bt resistance management Final report To prolong the utility of Bollgard II® against H. armigera, growers that use this tool must follow a resistance management plan (RMP). This strategy is largely based on information from studies of the ecology and population genetics of H. armigera, and the outputs of computer simulation models that use biological information to predict the likelihood of resistance under different scenarios. These models assume that any individuals which are resistant to Bollgard II® survive to successfully reproduce in cotton landscapes. In this project we developed novel methods to determine in the field how natural enemies in Bollgard II® versus unsprayed refuge crops affect the probability that Helicoverpa armigera will survive from hatching until adulthood. Part of this objective was testing how the application of pesticide in Bollgard II® fields to control sucking pests affects natural enemy communities and, in turn, survival of H. armigera. A secondary objective was to co-ordinate the collection of surviving Helicoverpa larvae from Bollgard II® crops and rear them for inclusion in the Bt resistance monitoring program. Survival of Helicoverpa larvae differed significantly across the main crops employed in the current Bollgard II® landscape but the particulars of this trend differed among small and medium larvae. Survival of small larvae was greater in pigeon pea and Bollgard II® cotton that was sprayed for sucking pests and mites compared with conventional cotton and unsprayed Bollgard II® cotton. However, this trend held during mid and late season but early in the season there was no difference in survival across the crops. Survival of medium larvae was greater in pigeon pea compared with conventional cotton and unsprayed Bollgard II® cotton and this trend was consistent across the period during which these crops are attractive. The similar survival in unsprayed Bollgard II® and conventional cotton is intuitive based on past work showing similar communities of natural enemies in these crops. The higher survival in pigeon pea (for both size classes) and Bollgard II® cotton that is sprayed (for small larvae) suggests that these crops may have fewer natural enemies compared with unsprayed Bollgard II® and conventional cotton. The survival results also suggest that spraying Bollgard II® fields for mirids and mites may reduce the abundance of natural enemies (relative to unsprayed Bollgard II® fields), and that this process affects mortality of smaller larvae. It is possible, for example, that sprays reduce numbers of predators that specialise on small larvae. These suggestions are supported by data on arthropod communities across replicate fields. In particular, spiders appear to play a significant role in mortality. For small and medium larvae there was a strong negative relationship between survival and abundance of spiders in open tents but not with any other category of predators (arthropods <5mm, arthropods 5mm or >, ants, ladybeetles) or parasitoids. Moreover, across replicate fields the abundance of spiders mirrored the mortality of larvae in open tents in the same crops. For small larvae there was a strong positive relationship between survival and the abundance of small non-predatory arthropods. In addition, across replicate fields the abundance of these arthropods opposed the mortality of larvae in open tents in the same crops. These results suggest that alternative small prey may improve survivorship of small larvae.During the past three seasons, surviving larvae were found in Bollgard II® fields on some properties in all main cotton valleys. We determined (through collaboration with CSE112) that Bt resistance, or the absence of Bt proteins in the host or surrounding plants, is not the mechanism allowing these larvae to survive on Bollgard II®. This information will be utilised in an upcoming forum to assist with reviewing the current Resistance Management Plan for Bt cotton.