Two sibling species of the spruce web-spinning sawfly Cephalcia fallenii (Hymenoptera : Pamphiliidae) in Europe

The spruce web-spinning sawfly Cephalacia fallenii is considered to be a minor pest defoliating spruces (Picea spp.) in Europe and northern Asia, and is characterized by a high degree of morphological polymorphism throughout its wide range. A sudden increase in population density observed in Central and southern Europe since 1976, strictly related to the dieback of large areas of spruce forests, made it possible to compare a large number of insects from different sites. The study was performed by combining field observations on epidemics and biological traits with analyses of allozymic, karyological and morphological characters. Two sibling species occurring together in all the study sites were identified by a diagnostic allozyme at the glucose phosphate isomerase (GPI) locus, karyotype differences, emergence times and the colour pattern of adults (light and dark). As the light form matches well with the lectotype of Lyda annulicornis, here designated, this species is redescribed on the basis of a large number of specimens. A new synonymy for the remaining taxa is proposed. Karyotype differences between the two siblings are substantial (C. fallenii, n = 18, 17M + 1A; C. annulicornis, n = 26, 13M + 13A), suggesting that chromosome rearrangements played a role in the speciation process.