Enhancing the biological control of leafrollers (Lepidoptera: Tortricidae) using floral resource subsidies in an organic vineyard in Marlborough, New Zealand

Abstract

In this thesis, experiments were conducted in both the laboratory and the field to determine whether the provision of floral resources to Dolichogenidea tasmanica Cameron (Hymenoptera: Braconidae) could enhance the biological control of leafrollers (Lepidoptera: Tortricidae) in an organic vineyard in Marlborough, New Zealand. Laboratory experiments were conducted to find a selective floral resource that could enhance the 'fitness' of the parasitoid, D. tasmanica without enhancing that of its host, the lightbrown apple moth, Epiphyas postvittana Walker (Lepidoptera: Tortricidae). From these experiments it was found that the longevity of adult female and male D. tasmanica could be enhanced significantly from 2.8 and 3.8 days, respectively, with water to 18.4 and 12.4 days, respectively, with buckwheat, Fagopyrum esculentum Moench, cv. Katowase. Also, adult E. postvittana 'fitness' was not enhanced when exposed to buckwheat and first-instar E. postvittana larvae 'preferred' grapevine to buckwheat leaves. Therefore, buckwheat was tested for its ability to enhance the biological control of E. postvittana in the vineyard. In field experiments in 2003, leafroller parasitoids were more abundant in areas of the vineyard planted with buckwheat and greater parasitism rates of naturally-occurring leafroller larvae were recorded in vineyard plots with buckwheat compared with control areas. In 2004, field experiments showed that rubidium chloride could be used to mark parasitoids feeding on buckwheat nectar and that D. tasmanica dispersed at least 30 m from buckwheat plants within a seven-day sampling period following feeding. Also, parasitism rates of leafroller larvae were greater adjacent to the buckwheat (41 %) than at 10 m from it (19 %). In a large-scale field experiment conducted in 2005, parasitism rates of naturally-occurring leafroller larvae were again found to be greater in areas of the vineyard planted with buckwheat and there were fewer larvae in grape bunches at harvest time in buckwheat compared with control areas. Therefore, the results of this work indicate that buckwheat may be used as a "selective food plant" to enhance the biological control of leafrollers in New Zealand vineyards. Future work could further explore whether buckwheat can reduce leafroller larvae in grape bunches to below economic thresholds, as this result is more likely to encourage grapegrower uptake of this technology.