title: Phytoseiid mites on unsprayed apple trees in Oregon, and other western states (USA): distributions, life-style types and relevance to commercial orchards.
abstract: In unsprayed apple trees in eastern Oregon, Galendromus flumenis (Chant), Galendromus occidentalis (Nesbitt), Typhlodromus caudiglans Schuster and Metaseiulus citri (Garman and McGregor) were common phytoseiid mites; common plant-feeding mites were the eriophyid, Aculus schlechtendali Nalepa, the brown mite, Bryobia rubrioculus (Scheuten) and Eotetranychus spp.; apple rust mites seemed to be the primary prey for phytoseiids; the spider mites, Tetranychus urticae Koch and Panonychus ulmi (Koch) were scarce except for a few local outbreaks; the stigmaeid Zetzellia mali (Ewing) was at 10% of sites and its densities were inversely related to phytoseiid densities; phytoseiids were absent at some sites, particularly at high elevations where winters are severe. In seven Oregon ecoregions, G. flumenis was often at lower elevations in valleys with moderate winters; T. caudiglans was often at higher elevations; G. occidentalis was often at intermediate elevations, in young trees, and near where pesticides were used; it dominated in unsprayed trees only in almost treeless, sage-covered areas; M. citri was usually in older apple trees near agriculture. In mixed phytoseiid populations, M. citri, a generalist, and G. occidentalis, a specialist, occurred more often than expected; G. occidentalis was mostly found with T. caudiglans, a generalist; G. flumenis, a generalist, occurred less with others, possibly because it competes with both specialists and generalists. Analyses of species' distributions with multiple regression and genetic models gave explanatory r2s of 0.019-0.318. Of 29 variables, altitude of site, intensity of agricultural management, tree age, plant types, and Z. mali levels helped explain phytoseiid species presence. In the western USA, G. flumenis dominated in middle-southern latitudes; T. caudiglans dominated in the north near the Canadian border; G. occidentalis dominated in middle latitudes in parts of Washington, Idaho, Montana, and Wyoming; M. citri was at a few sites in these four states. Distributional and independent variable data were used to predict species presence at sites in Oregon with a 70% success rate. We discuss phytoseiid life-style types, community dynamics, presence in organic/conventional orchards, and trends as more selective IPM methods are used in apple orchards.
authors.affiliation: Department of Entomology, Oregon State University, Corvallis, OR 97331-2907, USA. croftb@science.oregonstate.edu
authors.forename: B A
authors.initials: BA
authors.lastname: Croft
authors.forename: H K
authors.initials: HK
authors.lastname: Luh
mesh_terms: D000818:Animals; D002980:Climate; D017753:Ecosystem; D005260:Female; D016014:Linear Models; D027845:Malus / Q000469:parasitology*; D008858:Microscopy, Phase-Contrast; D008924:Mite Infestations / Q000453:epidemiology / Q000469:parasitology*; D008925:Mites / Q000145:classification / Q000254:growth & development*; D015999:Multivariate Analysis; D009922:Oregon / Q000453:epidemiology; D018515:Plant Leaves / Q000469:parasitology; D019366:Western World