Submitted to: Washington State Horticulture Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: November 10, 2002
Publication Date: February 1, 2003
Citation: Unruh, T.R. 2003. Habitat manipulation to increase parasitism of leafrollers and codling moth. Washington State Horticulture Association Proceedings. p.125-127. Interpretive Summary: Leafrollers are the second most damaging group of insects in Washington apple orchards. Biological control of leafrollers has proven unreliable, and the activity of beneficial insects that attack the leafrollers is often very low, especially in the first or spring generation of these pests. We found that parasitism of our pest leafrollers can be enhanced by making non-pest caterpillars on which these parasites can overwinter more available on the boundary of orchards. This is done by planting wild multifloral rose and strawberry gardens which act as a host for the strawberry leafroller. In Central Washington this leafroller is not a pest but a beneficial because its presence dramatically increases the abundance of parasites in nearby orchards that can control pest leafrollers. Enhancing biological control of pest leafrollers leads to a reduction of pesticide use in apple orchards.
Technical Abstract: Parasitism of leafrollers was measured in multiple orchards in Wapato, Washington. Tachinid flies caused half or more of the parasitism of leafrollers parasitized by the exotic wasp, Colpoclypeus florus, and were found most reliably in sites near riparian habitats especially in summer. In 2000 we planted gardens of wild rose, Rosa woodsii, next to orchards with no previous history of parasitism by C. florus. Gardens were infested with the Strawberry leafroller, Ancylis comptana, which is an important over- wintering host of C. florus in some riparian settings. Ancylis larvae subsequently became parasitized by C. florus in the fall of 2000. In 2001, leafrollers in nearby apple orchards showed high parasitism by C. florus and much higher parasitism overall than observed in 1999-2000. Gardens of rose stimulated C. florus parasitism in orchards for the rest of 2001 and throughout 2002. These manipulations demonstrate that the rose/Strawberry leafroller community produces significant orchard leafroller parasitism in the spring when it is usually very low, and that spring parasitism grows into even higher parasitism in the summer generation.