2003 Volume 38 Issue 3 Pages 369-377
The sugi bark borer, Semanotus japonicus, occurs naturally in Honshu, Shikoku, Sado Is., Oki Is., and Yaku Is. in Japan, and its main host tree is the Japanese cedar, Cryptomeria japonica. Because of a correspondence between the present distribution of geographical variation in the borer and the refugia of the Japanese cedar during the last full-glacial period, isolation of the cedar is thought to have caused differentiation in the borer between local populations. In this study, we used morphological information to elucidate the geographical differentiation of S. japonicus populations. Multivariate analyses were performed based on ten morphological characters for ten populations. Populations between the Pacific coast side and the Wakasa Bay area showed remarkable variation in morphological characters. Because the distribution of the refugia of the cedar coincided with the patterns of morphological variations in S. japonicus, it is suggested that the geographical structure of the present S. japonicus population was caused by isolation during the last glacial period. While vicariance is no longer a factor with the expansion of C. japonica's distribution, its past effects may have been important enough to influence the present genetic structure of S. japonicus.
