Great Basin Naturalist


The ability of Typhlodromus occidentalis to oviposit and numerically increase when consuming various life stage distributions of Tetranychus mcdanieli and Tetranychus pacificus were studied at several interaction levels. On field-collected apple leaves and 6×6 cm artificial substrates, oviposition rates and rates of increase (r) were higher when predators were fed populations of spider mites with high proportions of eggs, and larvae as compared to prey colonies composed mainly of deutonymphs-male adults and female adults. Feeding studies indicated that reproductive differences were mainly due to increased predation and food intake when predators were offered eggs and larvae of Tet. pacificus and a decreased capture and food consumption when only provided with the larger prey stages. Samples taken throughout a growing season in apple trees and an orchard suggested that during early-season, prey stage distributions were most favorable to predator increases and would undoubtedly contribute to a rapid numerical response by predators. The affect of less favorable stage distributions was much less apparent as these stage proportions occurred during short intervals in early season, at intermediate prey levels, and were most unfavorable at high densities or late season after spider mites overexploited their host plant.