Abstract. Psocids are small insects that feed primarily on fungi, algae, lichens and organic detritus. Although they are relatively common in forest ecosystems, the general patterns in their abundance and diversity in boreal forests are still poorly known. We report records of 20 species of psocids quantitatively collected from four species of woody plants (Pinus sylvestris, Picea abies, Betula pubescens and B. pendula) at 50 sites in northern Europe, located between 59° and 70°N and between 10° and 60°E. Seven species were found only on conifers, seven other species only on birches and six species inhabited both birches and conifers. The overall density of psocids was 18.9 ± 2.9 exx/kg (d.w. of plant material). Densities varied among the studied species of trees, being highest on P. abies and lowest on B. pendula. The species diversity was highest on B. pendula and lowest on B. pubescens. Both diversity and abundance of arboreal psocids in northern Europe decreased with latitude. However, due to the relatively low number of specimens collected, the conclusions about the diversity of psocids should be seen as tentative.

We aim to assess habitat and host-tree preferences of psocids (Insecta: Psocoptera) sampled in old-growth-forest biodiversity studies conducted during 1997–2003 in central and southern Finland. Thirty-one out of the recognized sixty-nine Finnish species were found in the samples, four of which (Elipsocus abdominalis, Reuterella helvimacula, Stenopsocus lachlani and Trichadenotecnum majus) might be associated with old-growth forests or with old trees. Psocidus flavonimbatus, a rare taiga species only previously known from the 19th century holotype from Estonia, was repeatedly collected in Kuhmo region, eastern Central Finland. This species is possibly associated with boreal spruce-dominated old-growth forests and likely to prefer Norway spruce as a host tree. We also provide new distribution data for several species and discuss their host-tree preferences.

About 120 years since its original description from Estonia (region of lake Peipus) the enigmatic species Psocus flavonimbatus Rostock, 1879 has been rediscovered in semi-natural spruce-dominated forests in Kuhmo, Central Finland. The species, which had tentatively been synonymized with Loensia variegata (Latreille, 1799), is here reinstated. Coloration and general morphology of both sexes and terminalia of females are described and illustrated. Unfortunately the few males available are all damaged, lacking abdomen. Without information on male terminalia it is impossible to assign the species to one of the modern genera of Psocidae. Therefore, it is here retained in the genus Psocus, pending further studies.