# Unexpected Persistence of the Predatory Mite Amblyseius andersoni Under Insecticide Exposure in Italian Apple Orchards

## TL;DR

The predatory mite Amblyseius andersoni survives pyrethroid insecticides in Italian apple orchards, offering potential for sustainable pest control.

## Contribution

The study reveals intraspecific variation in A. andersoni's resistance to pyrethroids, with implications for IPM strategies.

## Key findings

- A. andersoni populations in apple orchards survived pyrethroid applications without decline.
- Some A. andersoni strains showed high resistance to deltamethrin, while others were susceptible.
- Resistant strains exhibited no sub-lethal effects on reproduction after insecticide exposure.

## Abstract

Predatory mites are minute arthropods that play an important role in agroecosystems by feeding on pest species. Because they provide natural pest regulation and help keep mite pests under economic injury levels, protecting and enhancing these natural enemies is important for sustainable crop production. However, non-selective insecticides used against insect pests may also affect these beneficial predators. In this study, we examined how pyrethroid insecticides affect predatory mite communities dominated by Amblyseius andersoni in apple orchards. We also tested in the laboratory whether various populations of the predatory mite A. andersoni differed in their susceptibility to these chemicals. Field results showed that a number of A. andersoni populations survived insecticide applications, in particular those based on pyrethroids, and maintained stable populations. Laboratory tests showed higher survival of A. andersoni collected in fruit orchards when exposed to deltamethrin than those from other sources. Implications for IPM are discussed.

Predatory mites are key natural enemies in perennial crops, and their conservation is fundamental to ensure biocontrol of several pests. Yet their susceptibility to insecticides may compromise their role in Integrated Pest Management (IPM). In the past, pyrethroids proved to be poorly selective insecticides towards predatory mites, but in various countries their use recently increased in fruit orchards to counteract invasive pests. In this study, we assessed the effects of pyrethroids on the predatory mite Amblyseius andersoni through field experiments in apple orchards and laboratory assays on different strains. Field trials showed that A. andersoni populations remained unaffected by pyrethroid applications. Laboratory assays revealed intraspecific variation in A. andersoni populations: one commercial strain was highly susceptible to deltamethrin, whereas other commercial or field-collected strains were not affected, with no apparent sub-lethal effect on fecundity. These results underscore the contrasting susceptibility among predatory mite strains. From an IPM perspective, the lack of susceptibility to pyrethroids in A. andersoni may sustain biological control where insecticide use is unavoidable. Our findings stress the importance of evaluation procedures in toxicological studies, in particular the need to compare different strains, and of further investigation on predatory mite resistance. The implications for conservation programs in perennial cropping systems are addressed hereafter.