Bursaphelenchus species in conifers in Europe: distribution and morphological relationships.
The morphological relationship between European Bursaphelenchus species living in conifers was studied in order to provide key characters for their taxonomic identification. Several species have been newly described or recorded in Europe during the past few years and were morphologically investigated. Among the 28 conifer-inhabiting European species, four groups can be distinguished from each other by the number of lateral incisures, number and position of anal papillae of males and presence and size of a vulval flap of females. Two groups, each containing just one species show two and six lateral lines, respectively, whereas most Bursaphelenchus species belong to two groups, possessing either three or four incisures. Each of the last two groups can be divided into three subgroups, which can be differentiated by spicule shape, number and position of caudal papillae, presence and size of a vulval flap and some other features. A fifth group includes species with unclear group affiliation due to insufficient knowledge of their morphology. The B. xylophilus group (B. xylophilus, B. mucronatus and B. fraudulentus) with four lateral lines, unique spicule shape and characteristic position of the caudal papillae can clearly be differentiated from all other groups by morphology, also using only light microscopy. Within this group, B. xylophilus can clearly be differentiated morphologically from the other species, provided that adult specimens of both sexes are found and also provided that the round-tailed form of the species remains the only form present, as in Europe. Figures showing the important identification features of spicule shape and female tail shape are given for 28 species. A table shows the complete range of the most important morphometric measurements of these species. Data on the occurrence, host range and, as far as known, the vectors of these species were collected throughout Europe and references are given for each record.