Releases of insectary-reared Galendromus occidentalis (Acari: Phytoseiidae) in commercial apple orchards.

Galendromus occidentalis (Nesbitt) is one of several phytoseiid species that are available for purchase to supplement endemic predator populations that are not providing sufficient control of spider mites. We performed a series of releases of commercially reared G. occidentalis in commercial apple (Malus domestica Borkhausen) orchards in Washington from 2010 to 2012. Releases of up to 50,000 mites per acre did not lead to an increase in populations of predatory mites or to a decrease in populations of pest mites. Assessments of mite numbers in shipments and quality (survival and fecundity) of those mites indicated that the commercial insectary was correctly estimating the number of predatory mites in their shipments, and that predator quality was not different than a laboratory colony. Finally, a predator-prey model that used the intrinsic rates of increase of tetranychid prey and the prey consumption rate of the predator indicated that the density of G. occidentalis required to control the prey at the action threshold was not economically feasible. We conclude that G. occidentalis cannot be used to bring about short-term control via inundative releases in crops such as apple with large canopy volumes.