Comparative biology and pesticide susceptibility of Amblydromella caudiglans and Galendromus occidentalis as spider mite predators in apple orchards.

The successful integrated mite management program for Washington apples was based on conservation of the mite predator Galendromus occidentalis (Nesbitt). In the 1960s, this mite was assumed to be the only phytoseiid in Washington commercial apple orchards, due to its preference for the most common mite pest of that period, Tetranychus mcdanieli McGregor, as well as its resistance to organophosphate pesticides. A recent survey of phytoseiids in Washington apple found that another phytoseiid, Amblydromella caudiglans (Schuster) has become common. It is a more generalized predator than G. occidentalis (it is not a Tetranychus spp. specialist) and is not known to be organophosphate-resistant. A series of experiments was conducted to compare the life history, prey consumption, and pesticide tolerance of these two species. Galendromus occidentalis developed more quickly than A. caudiglans, but had slightly lower egg survival. Although A. caudiglans attacked more Tetranychus urticae Koch eggs than G. occidentalis, it could not reproduce on this diet. Both predators performed equally well on a diet of T. urticae protonymphs. Unlike G. occidentalis, A. caudiglans experienced significant mortality when exposed to carbaryl, azinphosmethyl, and bifenazate. Both predators experienced significant mortality due to imidacloprid and spinetoram. These results highlight the key differences between these two predators; the shift away from organophosphate use as well as the change in dominant mite pest to Panonychus ulmi (Koch) may be driving factors for the observed increased abundance of A. caudiglans in Washington apple.