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

Abstract

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.

Not all predators are equal: miticide non‐target effects and differential selectivity

“…Previous work on G. occidentalis and bifenazate treatment did not show a reduction in longevity or increased mortality, but a significant reduction in number of eggs, egg hatch, and larval survival has been reported . Additionally, bifenazate application was correlated with reduced orchard populations of the predatory mite Amblydromella caudiglans Schuster and caused moderate mortality in this species, emphasizing that the non‐target effects seen in laboratory studies have field‐level implications.…”

“…acequinocyl, cyflumetofen, bifenazate) tend to be labeled as selective for spider mite control, with some labels specifically indicating lack of harm to listed predatory mite (and other natural enemy) species. However, selective products can have non‐target effects on some phytoseiid species, but not others . Additionally, there is a lack of miticide selectivity information for some phytoseiids (e.g.…”

Meta‐analysis and review of pesticide non‐target effects on phytoseiids, key biological control agents

“…Like the meta‐analysis (Fig. 6), prior work has regularly found G. occidentalis to be less pesticide sensitive than other phytoseiids, particularly in regards to MOA 1 insecticides 10,71,80 …”

“…There is also evidence that bifenazate can significantly decrease N. fallacis populations in watermelon 70 and T. caudiglans populations in apple 10 . Therefore, even selective acaricides may be harmful, especially to more sensitive phytoseiid species 44,71 …”

“…6), prior work has regularly found G. occidentalis to be less pesticide sensitive than other phytoseiids, particularly in regards to MOA 1 insecticides. 10,71,80 Lack of pesticide sensitivity in G. occidentalis is likely due to resistance development; field-selected resistance to azinphosmethyl, carbaryl, and a variety of pyrethroids has been well-documented in this species. 81,82 Phytoseiids appeared to be more similar in their response to newer MOAs compared to older MOAs (Fig.…”