Phytoseiid (Acari: Mesostigmata) mite abundance and diversity in Belgian apple orchards

Abstract: Due to Typhlodromus pyri (Acari: Phytoseiidae) being resistant against the formerly used organophosphates and carbamates, it was for several decades the only phytoseiid in Belgian commercial apple orchards. The hypothesis that shifting from organophosphates to more selective pesticides changed phytoseiid mite diversity, is investigated. This study examines the mite species complexes in Integrated Pest Management (IPM) orchards, organic and unsprayed abandoned orchards in 2016 and 2017. A total of four phytoseiid species was observed: T. pyri, Amblyseius andersoni, Euseius finlandicus and Phytoseius horridus. T. pyri was the most dominant species: it was recorded in 23 IPM and organic orchards, and was dominant in 20. The total abundance of Tetranychidae and Phytoseiidae did not differ between different pest management systems. However, species composition did differ: significantly less T. pyri and more A. andersoni, E. finlandicus and P. horridus were found to unsprayed orchards compared to IPM and organic orchards, respectively. Apart from pest management, no other effect of the orchard factors on mite populations was found.