Submitted to: Washington State Horticulture Association Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/25/1999
Publication Date: N/A
Citation: Pfannenstiel, R.S., Unruh, T.R., Brunner, J.F. 1999. Biological control of leafrollers: prospects using habitat manipulation. Washington State Horticulture Association Proceedings. 95:145-149. Interpretive Summary: Control of codling moth with pheromones instead of insecticides has allowed two species of native leafrollers to become important pests of apples in the Pacific Northwest. Research was conducted on the biology of natural enemies of these leafrollers to promote the use of biological control and reduce pesticide use for their control. Observations showed that several parasitic wasps and flies can parasitize leafrollers at high rates, especially during the second generation of these pests. Incidence of parasitism was associated with low pesticide usage and the presence of alternative hosts for the parasitoids. These alternative hosts included exotic leafrollers feeding on native vegetation. Most notable was the strawberry leafroller, which is found attacking wild, multifloral rose in native habitats and also in garden strawberry plantings of Central Washington. Proximity to patches of these alternative hosts for the parasitoids, particularly the exotic parasitoid, Colpoclypeus florus, increased parasitism in nearby orchards. The results suggest that planting of multifloral rose and perhaps strawberries to increase parasitism can enhance leafroller biological control. This hypothesis will be tested in the coming year and may lead to dramatic reductions in pesticide use for leafroller control.
Technical Abstract: The leafrollers Pandemis pyrusana Kearfott and Choristoneura rosaceana (Harris) continue to be primary pests in pome fruits in the Pacific Northwest. Parasitoids can cause significant mortality to leafroller pests in pome fruits, but biological control has not been found reliable. Some important leafroller parasitoids rely on the availability of alternate hosts during periods when suitable hosts are unavailable in orchards. Alternate hosts are not usually available in close proximity to orchards and this may limit some parasitoids. An alternate host for the dominant leafroller parasitoid (C. florus) has been identified as A. comptana. Studies have shown that proximity to populations of A. comptana can increase leafroller parasitism in orchards. We predict that manipulation of orchard or near- orchard habitats to provide alternate hosts will increase parasitism and improve biological control. Specifically, augmenting orchard systems with plantings of wild roses and or strawberries and establishing large populations of A. comptana should increase parasitism of leafrollers in orchards and reduce both the need for pesticide applications the amount of damage caused by these leafrollers. Other studies suggested the proximity of orchards to non-orchard habitats may determine the intensity of leafroller parasitism. We also saw patterns suggesting an inhibition of biological control from regional patterns of pesticide use. Further studies into the importance of habitats containing alternate hosts and areawide patterns of