Nature of galleries, durability of boring scars, and density of Xylotrechus villioni (Villard) larvae (Coleoptera: Cerambycidae), on coniferous tree trunks

Spatial distributions and shapes of "whirl-like" scars on the trunks, made by gallery formation of mature larvae of Xylotrechus villioni (Villard) (Coleoptera: Cerambycidae), a primary borer of Abies and Picea coniferous trees in Japan, were investigated at an Abies firma Sieb. et Zucc. plantation in Hachiôji, Tokyo Pref., an A. firma natural stand in Miyama, Kyoto Pref. and an A. sachalinensis (Fr. Schm.) Mast. plantation in Imakane, Hokkaidô. Although all the forests investigated showed cumulative "whirl-like" scars on the tree trunks, a low density of existing larvae was inferred from the analyses of the locations and shapes of these scars. Mortality throughout the larval stages, as well as between the final phase of larva and the adult emergence, was suggested. Trunk analysis of a damaged A. firma tree showed that a "whirl-like" scar can remain on the trunk surface for as long as 27 years after the formation of the larval gallery. The most susceptible class of Abies trees had a diameter at the breast height of 35-45cm. "Whirl-like" scars were distributed more densely in the lower part of the trunks.