Phytoseiids in Washington commercial apple orchards: biodiversity and factors affecting abundance

Abstract

Galendromus occidentalis (Nesbitt) is an important biological control agent of spider mites (Acari: Tetranychidae) in Washington apple orchards. It was thought to be essentially the sole phytoseiid existing in this system, due in part to its resistance to commonly used orchard pesticides, and organophosphates in particular. To test this assumption, we conducted a survey of 102 commercial apple blocks in Washington to characterize the community of phytoseiid species. Seven phytoseiid species were found in our samples; G. occidentalis and Amblydromella caudiglans (Schuster) were found in the greatest abundance. We hypothesized that the gradual shift away from the use of organophosphates in recent decades may have caused the change in phytoseiid community structure. The survey data and information regarding the management, location, and surrounding habitat of each block were used to determine what factors affect phytoseiid abundances. Galendromus occidentalis abundance was positively affected by the use of conventional (vs. organic) spray programs, and the use of the acaricide bifenazate. Amblydromella caudiglans abundance was negatively affected by bifenazate use and positively affected by herbicide strip weediness; it was also less prevalent in 'Golden Delicious' blocks compared to other cultivars. These results indicate that A. caudiglans reaches higher abundances in orchards that lack certain agricultural disturbances, whereas G. occidentalis can survive in more disturbed environments. Surveys of this nature can provide valuable insight to potential drivers of community structure, allowing for the improvement of integrated pest management programs that incorporate conservation of newly recognized biological control agents such as A. caudiglans.

Effects of foliar apple trichomes on Galendromus occidentalis (Nesbitt) (Acari: Phytoseiidae): preferences, fecundity and prey consumption

“…The newer classification system for phytoseiid life styles even divides Type III generalists into subgroups based on host plant preferences (McMurtry et al ., ). Additionally, in a survey of Washington apple, populations of a generalist phytoseiid Amblydromella caudiglans (Schuster) were lower in ‘Golden Delicious’ compared with other cultivars, although cultivar had no effect on G. occidentalis abundance (Schmidt‐Jeffris et al ., ). Therefore, it is not entirely unexpected that G. occidentalis , a specialist, did not exhibit strong preferences for a cultivar in our assays.…”

“…In Washington apple orchards, Galendromus occidentalis (Nesbitt) is the most common phytoseiid species (Schmidt‐Jeffris et al ., ). It is an important biological control agent of the spider mite pests, Panonychus ulmi (Koch), Tetranychus urticae Koch and Tetranychus mcdanieli McGregor (Hoyt, ; Hoy, ).…”

“…Although small predatory hemipterans will consume phytoseiids (Cloutier & Johnson, ), these organisms are often scarce in Washington apple orchards. Another predatory mite Zetzellia mali (Ewing) is also known as an intraguild predator of phytoseiid eggs (Clements & Harmsen, ), although it is not found in significant abundance in the majority of commercial apple orchards (Thistlewood, ; Schmidt‐Jeffris et al ., ). Additionally, the apple growing regions of eastern Washington are arid (Kottek et al ., ) and so it is possible that trichomes may benefit G. occidentalis by providing a more humid microclimate.…”

Non‐target effects of herbicides on Tetranychus urticae and its predator, Phytoseiulus persimilis: implications for biological control

“…Weeds serve as green bridges between unmanaged areas and crop systems. For instance, weedy ground cover has been shown to increase phytoseiid abundance in orchard systems . Retention of weedy areas through reduced herbicide use or mowing can promote phytoseiid populations and enhance biological control .…”

“…For instance, weedy ground cover has been shown to increase phytoseiid abundance in orchard systems. 11,13,49 Retention of weedy areas through reduced herbicide use or mowing can promote phytoseiid populations and enhance biological control. 13,15,50 This has been attributed to the availability of weed pollen as a food resource 51 and to the shelter from ultraviolet radiation and desiccation provided by weedy ground cover.…”