Description of Bursaphelenchus piceae sp. n. (Nematoda: Parasitaphelenchinae) from larval galleries of the six-toothed spruce bark beetle, Pityogenes chalcographus (L.) (Coleoptera: Curculionidae: Scolytinae), in Norway spruce, Picea abies (L.) Karsten

Abstract

Bursaphelenchus piceae sp. n. is described from the bark of Norway spruce, Picea abies. Adults and propagative juveniles of the nematode are found in larval galleries of the six-toothed spruce bark beetle, Pityogenes chalcographus, while its dauer juveniles aggregate in Malpighian tubules of older larvae, pupae and adult beetles. The new species is characterised by the body length of 719 (530-945) μm in female and 632 (474-808) μm in male, its moderately slender body (a = 41.4 (35.4-50.2) and 42.6 (35.1-47.2) in female and male, respectively), and small spicules (16.0 (14.0-18.3) μm along arc and 13.7 (12.2-15.5) μm along chord). The extended anterior vulval lip in female, lateral fields with four incisures, long post-uterine sac extending for 67-91% of vulva-anus distance, and number (7) and arrangement of male caudal papillae suggest that B. piceae sp. n. is closely related to the xylophilus-group yet it differs by the relatively small, claw-like spicules with no cucullus at the tip. The close relation of B. piceae sp. n. to the xylophilus-group has been confirmed by DNA sequencing and phylogenetic analysis. Morphologically B. piceae sp. n. most closely resembles B. tokyoensis and B. fagi but can be separated from both by the unique shape of the spicules. The taxonomic separation of the new species is also confirmed by the unique molecular profile of the ITS region (ITS-RFLP). The presence of dauer juveniles of B. piceae sp. n. in Malpighian tubules of adult P. chalcographus may lead to extensive damage to this organ as shown by local expansion of the tubule basement membrane and degradation of its cellular epithelium. Detailed phylogenetic analysis revealed that B. piceae sp. n. together with five other bark beetle-associated Bursaphelenchus species, namely B. trypophloei, B. masseyi, B. tiliae, B. tokyoensis and B. fagi, constitutes a small phylogenetic clade that is most closely located to, but separate from, the xylophilus-group.