In the first contribution a new Psylla species is described, viz. P. betulaenanae, n.sp. On the basis of larval characters this species is stated to be closely related to Psylla betulae (L.), P. alni (L.), P. fusca (Zett.) and the American P. carpinicola (Crawford), these species together constituting Psylla s.str. (type Psylla alni). In the second contribution the larval instars of Psylla foersteri Flor are described and this species is made the type of subgenus Labyrinthopsylla, n.subg. The third contribution deals with our remaining Psylla species which are arranged into three new subgenera, viz. Cacopsylla (type mali (Schmiedb.)), Chamaepsylla (type hartigi Flor), and Hepatopsylla (type nigrita (Zett.)). Also this subdivision is based on larval characters. The fourth contribution is a tentative key to the Swedish Psylla species in the 5th larval instar. No tenable characters for the separation of nigrita (Zett.), elegantula (Zett.), and klapaleki Sulc were discovered, however.