Submitted to: Western Orchard Pest and Disease Management Conference
Publication Type: Proceedings
Publication Acceptance Date: 12/1/2002
Publication Date: 1/15/2003
Citation: Unruh, T.R. 2003. Rose plantings increase leafroller parasitism in orchards: a story for the Rose City. Western Orchard Pest and Disease Management Conference. p.24-26. 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 enhance 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 leafrollert is not a pest but a beneficial because its presence dramatically increase 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: In 1999-2002 parasitism of leafrollers was measured in multiple orchards embedded in a 1000-hectare landscape mosaic in Wapato Washington. Using field exposure of lab-reared, larval Pandemis pyrusana we found parasitism was very low in spring and modest in summer generations. Roughly half of the parasitism was caused by 2 tachinids and the remaining half by 3 wasp parasitoids. Parasitism by the exotic wasp, Colpoclypeus florus, was found most reliably in sites near riparian habitats and almost exclusively in summer. In late summer of 2000 we planted 4 gardens of wild rose, Rosa woodsii, next to orchards at sites distant from riparian habitats 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 the spring of 2001, sentinel Pandemis in both gardens and nearby apple orchards showed high parasitism by C. florus and much higher parasitism overall than observed in 1999-2000. Gardens acted as foci of C. florus parasitism in orchards through the 3 subsequent leafroller generations in 2001 and 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.