The influence of floral resource subsidies on parasitism rates of leafrollers (Lepidoptera: Tortricidae) in New Zealand vineyards

Biological control of pests in agroecosystems may be enhanced by the use of habitat manipulation techniques to provide floral and other ‘resource subsidies’ for natural enemies. This was examined in vineyards by adding flowering buckwheat (Fagopyrum esculentum Moench) and assessing the effect of this on the parasitism rate of leafroller (Lepidoptera: Tortricidae) larvae. Leafroller larvae were collected from vines in plots with and without buckwheat flowers at two commercial vineyards in Marlborough, New Zealand. At one vineyard, the parasitism of these pests was increased by more than 50% when buckwheat flowers were present. At the other, buckwheat had no effect, however leafroller populations were lower and insecticides had been used in part of the experiment. The presence of buckwheat did not reduce leafroller abundance during the two months of the study. These results show that habitat manipulation, by providing floral resource subsidies for parasitoids, can enhance parasitism rate. However, the value of this technique for reducing damage done by leafrollers in the vineyard system studied remains to be determined.