Comparative emigration, immigration, and colonization of apple by Metaseiulus occidentalis Nesbitt and Typhlodromus pyri Scheuten (Acarina: Phytoseiidae)

Dispersal and colonization of young potted apple trees by the spider-mite predators Metaseiulus occidentalis Nesbitt and Typhlodromus pyri Scheuten were studied in the Hood River Valley of Oregon. Experimental mini-orchards of 10 four-year old potted apple trees were established at distances of 0, 10, and 100 m downwind from commercial apple orchards. Mini-orchards were inoculated with Panonychus ulmi and Tetranychus urticae to provide a prey resource for predatory mites. The commercial orchards harbored either M. occidentalis or T. pyri, or both. Emigration from the source orchards was estimated by the number of adult females found in mini-orchards located 0 m downwind. Immigration was measured by the initial presence of adult females in mini-orchards at 10 and 100 m. Colonization was interpreted as the presence of predatory mite eggs or nymphal stages in samples from the 10 and 100 m mini-orchards. Leaf samples were taken either biweekly (1987) or weekly (1988). Metaseiulus occidentalis and T. pyri both emigrated from the source orchard trees to the experimental mini-orchards 0 m downwind. Typhlodromus pyri rarely immigrated to the mini-orchards 10 m downwind, while M. occidentalis reached the potted trees at 10 m soon after the mini-orchards were established. Metaseiulus occidentalis also immigrated to the experimental mini-orchards 100 m downwind, whereas T. pyri did not. In all cases, immigration of M. occidentalis to the experimental mini-orchards was more frequent than for T. pyri. Also at all sites, M. occidentalis colonized the young apple trees at a faster rate than did T. pyri

Effect of pesticides on integrated mite management in Washington State

The effect of pesticides used against codling moth, Cydia pomonella L., on integrated mite management was studied for three years in five or six commercial apple orchards in central Washington. Phytophagous and predatory mites were counted throughout the season in blocks ranging from 0.4-1.6 ha in size treated with four codling moth insecticides. In one year of the study (2006), five out of six orchards experienced elevated mite densities relative to the standard. In four orchards, novaluron caused a 3.0-16.9× increase in mite populations; acetamiprid caused a 2.6-3.4× increase, and thiacloprid caused a 1.7-13.8× increase. In the fifth orchard, the organophosphate standard had an extremely high mite population, in addition to all three experimental treatments. In 2005 and 2007, only one or two orchards had elevated mite levels in the novaluron, acetamiprid, and thiacloprid treatments. Additive effects of codling moth and thinning programs were evaluated in small plot research trials. Treatments with all three elements [1) codling moth insecticide; 2) calcium polysulfide; 3) carbaryl] produced the highest levels ofspider mites. Three sulfur-containing products (calcium polysulfide, ammonium thiosulfate, and dry flowable sulfur) were evaluated for their effect onGalandromus occidentalis (Nesbitt) and apple rust mite, Aculus schlechtendali (Nalepa). All three materials caused suppressed G. occidentalis numbers. Calcium polysulfide caused the greatest reduction in apple rust mite numbers, ammonium thiosulfate the least reduction, with dry flowable sulfur intermediate between the two. Additive effects of codling moth materials, carbaryl, and sulfur-containing products may be causing increased mite levels in Washington orchards