Enhanced conservation biological control of light brown apple moth in vineyards

Abstract

The light brown apple moth (LBAM), Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae), is the most damaging insect pest of wine grapes in Australia. Biological control contributes to the management of LBAM. This project aims to enhance the conservation biological control of LBAM by examining how the provision of alternative hosts and native flowering plants can sustain parasitoids like Dolichogenidea tasmanica (Cameron) (Hymenoptera: Braconidae). Native plants and alternative host insects that could support conservation biological control of LBAM in South Australian vineyards are evaluated. The contribution that D. tasmanica makes to biological control of LBAM would be more reliable if this wasp parasitises common alternative hosts, maintains populations on them when the grapevines are dormant, and then moves to attack LBAM when it reinvades vineyards. This study examined the foraging behaviour of D. tasmanica on LBAM and two tortricid species that are associated with vineyards, Acropolitis rudisana (Walker) and Merophyas divulsana (Walker). The reciprocal responses of these insect hosts were also studied to determine their susceptibility to wasp attack. During behavioural assays, all hosts were accepted by D. tasmanica with high parasitism rates. The parasitoid responded differently to different host species. These experiments indicate that populations of D. tasmanica should be conserved, and LBAM more reliably suppressed, if the alternative hosts, M. divulsana and A. rudisana, are present. Host choice between E. postvittana and M. dilvusana by D. tasmanica was also studied in a wind tunnel, where the wasp could express its natural searching behaviour. Choices tests were conducted to examine how natal hosts, host stages and the wasp’s experiences could affect the landing selections of D. tasmanica. Developmental outcomes of parasitoids on different host species were also examined. D. tasmanica exhibited no clear preference for either host. Host species did not affect the body size of the wasp, but did influence its developmental time, probably as a result of differences in the host’s body sizes. The sex ratio of the wasp did not vary between these host species. These results suggest that M. divulsana is a promising alternative host species to support parasitoid populations in vineyards. A field study was conducted to evaluate the potential impacts of candidate plants on biological control of leafrollers, especially LBAM. Five species were planted beside vineyards to provide shelter, nectar and alternative hosts for beneficial insects. The plants were Bursaria spinosa, Leptospermum lanigerum, Hakea mitchellii, Melaleuca lanceolata and Myoporum petiolatum. Similar leafroller abundances and parasitism rates were found between vineyard rows adjacent to the native plants compared to rows furthest from them. The absence of a difference was possibly due to the proximity of the experimental treatment areas and the movement of parasitoids. The results, including increasing parasitoid diversity over time, imply potential benefits of the plants for better leafroller management. The results from my studies suggest that selected supplementary resources can benefit parasitoids and thereby stabilise or enhance biological control of LBAM in vineyards. This research provides a foundation to develop strategies to better suppress LBAM by facilitating more stable biological control.