Aprionus Kieffer, 1894 is one of the most species-rich genera of the fungivorous subfamily Micromyinae (family Cecidomyiidae, gall midges). Eighteen new species of this genus are described here from different parts of the Palearctic region based on morphological characters of male adults: Aprionus balduri sp. nov. (Norway, Sweden), A. bestlae sp. nov. (Sweden, Czech Republic), A. borri sp. nov. (Sweden), A. fontanus sp. nov. (Germany), A. friggae sp. nov. (Sweden), A. fujisanensis sp. nov. (Japan), A. hugini sp. nov. (Sweden, Germany), A. magnii sp. nov. (Sweden), A. montivagus sp. nov. (Germany, Russia), A. munini sp. nov. (Sweden, Germany, Hungary), A. odini sp. nov. (Sweden), A. ogawaensis sp. nov. (Japan), A. sifae sp. nov. (Sweden), A. sleipniri sp. nov. (Sweden), A. surtri sp. nov. (Sweden), A. thori sp. nov. (Sweden), A. tyri sp. nov. (Sweden), and A. ymiri sp. nov. (Sweden, Finland). These species are classified with the angulatus, halteratus and smirnovi groups, or remain unclassified within the genus Aprionus. The styloideus subgroup of the halteratus group is established for seven species (four described here as new) with generally similar male genitalic morphology. Aprionus paludosus Jaschhof & Mamaev, 1997 is revived from synonymy with A. styloideus Mamaev & Berest, 1990, and both species are redescribed.
Gall midges, fungivores, morphology, male genitalia.