Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2013
Publication Date: 10/17/2013
Publication URL: http://handle.nal.usda.gov/10113/58291
Citation: Schmidt, R.A., Beers, E.H., Unruh, T.R., Horton, D.R. 2013. Releases of insectary-reared Galendromus occidentalis (Acari: Phytoseiidae) in commercial apple orchards. Journal of Economic Entomology. 106(5):1996-2005. Interpretive Summary: Spider mites such as the European red mite are sporadic pests of apple trees especially when their major predator, Galendromus occidentalis (Nesbitt) is disrupted by insecticides or is otherwise at too low of levels to control the pest. USDA-ARS scientists from Wapato WA, working with Washington State University scientists at Wenatchee WA, tested the feasibility of mass releases of G. occidentalis predator into apple orchards to suppress such outbreaks. We released commercially produced G. occidentalis into commercial apple orchards in experiments in 2010, 2011 and 2012. Releases of up to 50,000 mites per acre did not lead to increased population densities of predatory mites in the trees nor did we observe decreases in population densities of the pest mites. A mathematical model simulating the reproductive rates of the pest mite and consumption rates of the predator indicated that the numbers of G. occidentalis needed to control spider mites using mass releases was too high to be economically feasible for grower use.
Technical Abstract: 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, 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 which 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.