Beech gall midge gall

M. fagi is classified as a major pest, local and occasional, especially on young trees in submountain and mountain zones (Skuhravá and Roques, 2000). According to the four-degree scale for evaluation of harmfulness of forest pests, M. fagi belongs in the second group that includes species which, after attack, significantly reduce the assimilation processes of the tree (Skuhravý and Skuhravá, 1996).