Enhancing biological control of leafrollers (Lepidoptera : Tortricidae) bysowing buckwheat (Fagopyrum esculentum) in an orchard

Two successive trials were carried out in stone-fruit and apple orchards in the summers of 1994-95 and 1995-96 respectively to determine the effect of floral resources on leafroller parasitoid numbers. Orchards were divided i nto eight blocks, each containing one replicate of a control and a treatmen t. The treatment had buckwheat (Fagopyrum esculentum Moench) drilled (as 3 m x 2 m plots) in the centre of each replicate, while the control areas wer e kept weed free with herbicides. Catches of parasitoids in yellow pan trap s were compared between the control and treatment areas. In the first trial , on average 10 times more parasitoids were captured in the buckwheat plots than in the controls. However; few of the parasitoids were natural enemies of leafrollers; the catches were dominated by Anacharis sp., a parasitoid of the brown lacewing (Micromus tasmaniae Walker), itself a beneficial inse ct. Leafrollers were very rare in this orchard, which explains the absence of their parasitoids in the traps. In the second season, with the experimen t conducted in an orchard with a history of leafroller populations, higher numbers of Anacharis sp. were again caught in buckwheat than in control plo ts. However, significantly higher (34% compared with 20%) levels (P < 0.05) of parasitism (by Dolichogenidea tasmanica (Cameron)) of released leafroll er larvae were observed in buckwheat plots than in controls, despite fire s mall plot size. Also, higher numbers of D. tasmanica were captured in yello w sticky traps 2 m above the buckwheat than in the equivalent position in t he control plots.