Enhancing Biological Control of Leafrollers (Lepidoptera: Tortricidae) by Sowing Buckwheat (Fagopyrum esculentum) in an Orchard

Abstract

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 into eight blocks, each containing one replicate of a control and a treatment. The treatment had buckwheat (Fagopyrum esculentum Moench) drilled (as 3 m 2 m plots) in the centre of each replicate, while the control areas were kept weed free with herbicides. Catches of parasitoids in yellow pan traps 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 insect. Leafrollers were very rare in this orchard, which explains the absence of their parasitoids in the traps. In the second season, with the experiment conducted in an orchard with a history of leafroller populations, higher numbers of Anacharis sp. were again caught in buckwheat than in control plots. However, significantly higher (34% compared with 20%) levels (P< 0.05) of parasitism (by Dolichogenidea tasmanica (Cameron)) of released leafroller larvae were observed in buckwheat plots than in controls, despite the small plot size. Also, higher numbers of D. tasmanica were captured in yellow sticky traps 2 m above the buckwheat than in the equivalent position in the control plots.