Harmfulness of eriophyid mites (Eriophyoidea, Acari) causing galls on trees and shrubs in the Czech Republic

Fifteen eriophyid mite species are the most abundant species in the Czech Republic from which four, viz. Eriophyes fraxinivorus on Fraxinus excelsior, E. platanoideus on Acer platanoides, Phytoptus pyri on Pyrus communis and Stenacis triradiatus on various species of Salix injure their host plants and are evaluated as pests. The weight of the leaves attacked by eriophyid mites increase with increasing number of galls pro leaf but the surface of attacked leaves decrease with increasing attack. Harmfulness of eriophyid mites manifests by reducing of assimilation processes, retardation of growth, precocious drying and fall-off of attacked leaves. Heavily attacked young shrubs and trees may dry and decease.