Phenology and structure of a phytoseiid community in an insecticide-free apple orchard.

Commercial orchards have acarine communities that are reduced in biological diversity compared to their undisturbed counterparts. Examining the phenology of an unsprayed orchard allows for the examination of non-pesticide factors that drive changes in populations. This study examined the mite community in a largely unsprayed research orchard in 2013–2014. The phytoseiids Galendromus flumenis (Chant), Amblydromella caudiglans (Schuster), Kampimodromus corylosus Kolodochka, and Galendromus occidentalis (Nesbitt) were found, in addition to Zetzellia mali (Ewing) and Aculus schlechtendali (Nalepa). Although G. occidentalis is typically the dominant phytoseiid in commercial orchards, G. flumenis was much more abundant in this unsprayed block. Aculus schlechtendali appeared to be the main source of prey for all predator species. The availability of this prey item and the lack of pesticides are likely the factors that allowed for G. flumenis to reach high abundances. Tetranychids were scarce, emphasizing the role of these mites as induced pests; without the application of disruptive sprays, the predatory mite community was able to maintain biological control. This study demonstrates that the species complex of generalist phytoseiids that is present in orchard systems undisturbed by pesticides is sufficient to maintain spider mite populations below damaging levels throughout the season.