Abstract
Many phytoseiid mites are predators of orchard spider mites. Of the species in northern Utah, Typhlodromus occidentalis (Nesbitt) is most abundant in apple orchards. Several other phytoseiid mites are found on apple trees in Utah, the most frequently encountered are Amblyseius fallacis (Garman) and T. mcgregori Chant. T. occidentalis was studied, using Tetranychus urticae Koch as prey. Adult females were found during the winter and early spring under the matted cover crop and tree bark. Laboratory and field observations suggested that there were at least 10 generations a season. The stages of development were egg, larva, protonymph, deutonymph, and adult; with partial quiescence between instars. The male of Typhlodromus occidentalis passed through a distinct deutonymph stage, as did the female. The average developmental time from egg to adult was 6.3 days at 75°F. The females mated once; the males several times. When ample numbers of tetranychid mites were present, they fed only as predators. In the absence of prey, the phytoseiids occasionally fed on pollen and apple foliage. Immature forms could not complete their development without spider mites as food. Adults would not lay eggs without feeding on mites, although they could survive for several weeks. They did not become cannibalistic, even when starved.
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