Habitat manipulation to enhance the biological control of orchard pests : A dissertation submitted in partial fulfillment of the requirements for the degree of Bachelor of Horticultural Science with Honours at Lincoln University

Abstract

Leafroller caterpillars (Lepidoptera: Tortricidae) are significant pests of New Zealand export fruit crops. A dependence on high agrichemical inputs for leafroller control has led to low diversity within orchard systems and natural enemies of leafrollers have been reduced to a negligible role in biological control. Information is needed to establish the potential of natural enemies of leafrollers in a low pesticide regime, especially if plant diversity in the orchard can be enhanced. One method for doing the latter is to provide floral resources for the parasitic wasps which parasitise leafrollers - the female parasitoids need pollen and nectar for egg maturation. In this work, an orchard of 384 stone-fruit trees was divided into eight blocks, each containing one replicate of eacti treatment. One treatment had buckwheat (Fagopyrum escu/entum Moench.) drilled in the centre of each 24-tree replicate, with control areas kept weed free with herbicides. Four yellow pan traps (with water,detergent and preservative) for catching insects were placed in the centre of each of the 16 plots and were emptied weekly. The catches of parasitoids were compared between the experimental and control treatments for each sampling date. There were on average ten times more parasitoids 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., parasitoids of the brown lacewing (Micromus tasmaniae Walker.), itself a beneficial insect. Leafrollers were very rare in this orchard, which explains the absence of their own parasitoids in the traps. However, the principle that a simply-achieved increase in orchard diversity can enhance populations of parasitoids has been clearly demonstrated in this work. In the future, the trial will be repeated in an unsprayed apple orchard, with a history of leafroller outbreaks. Buckwheat cultivars vary in their suitability for providing floral resources to natural enemies. The phenological attributes of twelve cultivars of buckwheat were compared. The buckwheat cultivars were sown at monthly intervals in two-metre long rows at Lincoln University, starting in August, 1994. Clear differences in the time from sowing to flowering were evident, with a Mongolian variety being very early, and others, such as the Japanese tetraploid, Miyazairai, Nagano, the un-named variety and Miyazaki Ootubu being slow to flower under New Zealand South Island conditions. The possibility of assessing the buckwheat cultivars for beneficial insect preference is discussed.