Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2012
Publication Date: 5/26/2012
Citation: Pfannenstiel, R.S., Mackey, B.E., Unruh, T.R. 2012. Leafroller parasitism across an orchard landscape in central Washington and effect of neighboring rose habitats on parasitism. Biological Control. 62:152-161. dx.doi.org/10.1016/j.biocontrol.2012.04.006. Interpretive Summary: Leafrollers are significant insect pests of apple, pear, and cherry orchards, but can be managed by natural enemies such as parasitoids. Researchers at the USDA-ARS Yakima Agricultural Research Laboratory in Wapato, Washington measured parasitism of pest leafrollers in 1000 hectares of orchard and other crops for two years. They demonstrated that beneficial insect activity was greater near riparian habitats along the Yakima River. One key plant-insect community, wild roses with a non-pest leafroller, supported an important natural enemy of pest leafrollers in the orchards. This research set the ground work for modifying near orchard habitats to enhance biological control within orchards.
Technical Abstract: Parasitiam of sentinel Pandemis pyrusana (Tortricidae) leafroller larvae on potted apple trees placed in apple, pear and cherry orchards within a 2000 hectare landscape mosaic in south-central Washington were measured in 1999-2000. Parasitism rates of sentinels averaged 15% in spring and 31% in summer during the first and second leafroller larval generations, respectively. Roughly two thirds of spring and summer parasitism was caused by Nilea erecta (Tachinidae) and the remaining third was by three wasp parasitoids; the exotic Colpoclypeus florus (Eulophidae), Apanteles polychrosidis and Oncophanes americanus (Braconidae). Spring and summer parasitism by O. americanus and C. florus declined with increasing distance from riparian habitats along the Yakima River. No statistical associatioin was evident for parasitism by any species with pesticide use in orchard blocks. Parasitism rates of sentinels placed in orchards in fall, when leafrollers in the field are small larvae seeking overwintering sites, exceeded 95% and was dominated by C. florus. Sentineals placed in two orchards adjacent to patches of the Wood's rose (Rosaceae; Rosa woodsii), naturally infested with the strawberry leafroller, Ancylis comptana (Tortrididae) showed parasitism rates of sentinal leafrollers approaching 100% in spring at one site and in summer at a second site and was dominated by C. florus. These observations suggest that the non-pest leafroller, A. comptana, on multifloral rose is a valuable overwintering host for C. florus and manipulation of habitats adjacent to orchard to support this simple insect community may help enhance parasitism and biological control of pest leafrollers in orchards.