Amblydromella caudiglans: A newcomer to the integrated pest management of spider mites?

Management of pest species, including spider mites (Acari: Tetranychidae), in Washington apple orchards has changed significantly in the past several decades. Organophosphates are being phased out and exchanged for “softer” pesticides. Evaluations of pesticides for effects on natural enemies are becoming increasingly common. Additionally, Panonychus ulmi has replaced Tetranychus mcdanieli as the common pest species in Washington orchards. One critical aspect of spider mite biological control is Galendromus occidentalis (Acari: Phytoseiidae). Despite the historical recognition of this predatory mite’s role in biological control, it has only been assumed that it is the only species that can survive “hard” pesticide applications. Therefore, a survey was conducted to evaluate this claim. Leaf samples were collected from sites throughout eastern Washington. All phytoseiids were removed from the leaves, slide mounted, and identified to species. Galendromus occidentalis was the most common species, but several other species were present in lower abundances. Most noteworthy is the presence of Amblydromella caudiglans as the dominant species in several conventional orchards. It is possible that its high populations are due to the movement away from organophosphate use. The prevalence of A. caudiglans could also be attributed to the transition from a preferred prey of G. occidentalis to that of A. caudiglans as the most common pest. Further research should determine the role of A. caudiglans as a biological control agent. As a more generalized predator, A. caudiglans may be more efficient than G. occidentalis at maintaining pest mite populations, especially P. ulmi, below outbreak levels.