Abstract
The density, prevalence, intensity of spider mites populations on 16 species and cultivars of willow grown in ornamental plant nurseries in Poland were determined. The investigations showed that the willow taxa most threatened by the development of large Tetranychidae populations were Salix helvetica and Salix caprea Kilmarnock. Phytoseiidae species co-occurring with the spider mites on the investigated plants and willows grown in forests were identified. The association of particular phytoseiid species with the habitat and prey species was evaluated. Predatory mites, such as Typhlodromus (Typhlodromus) pyri Scheuten, Phytoseius echinus Wainstein & Arutunjan, Phytoseius macropilis (Banks) and Phytoseius juvenis Wainstein & Arutunjan were observed in nurseries, while in the forests Euseius finlandicus (Oudemans) or Phytoseius severus (Wainstein & Vartapetov) occurred, along with P. echinus and P. macropilis.