Until recently, the system of classification of the Psylloidea was discussed exclusively on the basis of adult morphology. The system proposed by Burckhardt is followed here. With a few exceptions, the illustrations for the present book were prepared by the author. The terminalia of all species (m/f) have been figured. Furthermore, the 5th instar nymphs of nearly all the species have been keyed and figured.
For each species, the distribution in and outside Denmark and Fennoscandia is briefly given. Information concerning the Scandinavian countries was compiled from literature and from the author's records based on identifications for museums and private collectors over the last 53 years. Distribution data for outside Fennoscandia and Denmark were derived mainly from Klimaszewski (1973). Information on the biology of the species has been compiled from the literature and from the author's observations.
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.
Examination of the single male paratype of Psylla myrtilli W. Wagner revealed that it belongs to a different species, Psylla corcontum Šulc. The genitalia of two males from the USSR considered to be the genuine myrtilli, are reproduced. A related new species from the Far East is described under the name Psylla amabilis.
Two new leafhopper species, Cosmotettix evanescens from SW Sweden, and Lebradea icarus from S Finland, are described. Figures of genitalia and certain other features are given together with keys for Fennoscandian and Palaearctic spp., respectively.
In his revision of the Psyllids of Zetterstedt (Ossiannilsson, I942), the author identified Chermes viridulus Zett. with Trioza cirsii Löw. By a study of preimaginal characters this is now found to be wrong and it is stated that Trioza viridula (Zett.) and Trioza cirsii Löw are distinct though closely related species. Details of their male and female genitalia and the microsculpture of the under side of their fore wings are reproduced for comparison. Figures of the larval instars of viridula and cirsii and the related agrophila Löw showing their chaetotaxy are also given. A key for the separation of these larvae and some data on the biology and distribution of these species in Sweden terminate the present paper.
It is stated that two Allygus species have been mixed up under the name of Allygus mixtus (F.), one of them being A. mixtus in the sense of Ribaut (1952). Ferrari (1882) described 4 "varieties" of mixtus. By examination of the syntypes of Ferrari and designation of Iectotypes the I established that the "nameless" species should be known under the name of Allygus communis (Ferrari).