Materials to the knowledge of Polish sawflies. The genus Dolerus Panzer, 1801 (Hymenoptera, Symphyta, Tenthredinidae, Selandriinae). Part XVIII Dolerus (Achaetoprion) pachycerus Hartig, 1837 with observations on its biology and a key for identification of larvae of subgenus Achaetoprion Goulet, 1986

Information is presented on the occurrence in Poland of Dolerus (Achaetoprion) pachycerus Hartig, a sawfly species new to the fauna of the country. The breeded larvae fed on Juncus compressus Jacq., which is a new host plant record. Additionally, the flight periods of particular species of the subgenus Achaetoprion Goulet are discussed and graphically presented. Finally, an identification key is provided for the last feeding stages of larvae of Polands species of the genus Dolerus Panz. found on rushes.