Submitted to: American Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2008
Publication Date: 3/19/2009
Citation: Horton, D.R., Jones, V.P., Unruh, T.R. 2009. Use of a New Immunomarking Method to Assess Movement by Generalist Predators Between a Cover Crop and Tree Canopy in a Pear Orchard. American Entomologist. Vol 55(1):49-56. Interpretive Summary: Problem Statement: Many insect pests of apple and pear are commonly controlled with pesticide cover sprays. More effective biological control of these pests by predatory insects would reduce pesticide use. Scientists with USDA-ARS, Yakima Agricultural Research Laboratory, Wapato, WA and the Washington Tree Fruit Research and Extension Center, Washington State University, Wenatchee, WA used newly developed technology that allows marking of large segments of vegetation and associated insects, to assess movement by insects from a legume cover crop into pear trees. Data collected over the 3 years of study showed that there was substantial movement by predators from cover crop into trees, even in insects not known to regularly inhabit understory vegetation. These data will allow growers and scientists to make informed decisions about using cover crops in orchards to promote biological control.
Technical Abstract: Poor understanding of natural enemy movement between cover crop and crop habitats has slowed progress in using cover crops to enhance biological control of pest arthropods in agricultural systems. To address this problem we used an egg-albumin immunomarker sprayed on a legume cover crop to monitor movement by generalist predators from the cover crop into the canopy of pear trees in a Central Washington State pear orchard. Generalist predators in four taxa (Heteroptera, Coccinellidae, Chrysopidae, Araneae) were collected from both cover crop and pear tree canopy, and tested using enzyme-linked immunoassay (ELISA) methods to determine if the marker was present. In the three years of study, 90% of arthropods collected from the cover crop carried the marker, indicating that we had excellent coverage with the marker solution. Between 17 and 29% (depending upon the year of study) of the approximately 2000 specimens collected from the tree canopy were also found to be marked, which is evidence that a large percentage of the generalist predator community in the tree canopy had originated from or had visited the legume cover crop. These specimens included even spiders and immature insects, ehich presumably colonized the tree either by walking up the tree trunk or (for spiders) by ballooning into the canopy. The technology used here provides a powerful tool for assessing the effects of habitat management on movement of generalist predators in crop systems.