Components of Steamed and Non-Steamed Japanese Larch (Larix leptolepis (Sieb. et Zucc.) Gord.) Heartwood Affecting the Feeding Behavior of the Subterranean Termite, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae)

Abstract

Summary The attraction of steamed Japanese larch (Larix leptolepis (Sieb. et Zucc.) Gord.) heartwood to the subterranean termite, Coptotermes formosanus Shiraki was investigated. Hot-water extracts of the steamed and the non-steamed larch woods were sequentially extracted with n-hexane, diethyl ether, and ethyl acetate. Furthermore, the residual water-soluble fraction of the steamed wood was fractionated by column chromatography using an Amberlite XAD-2 resin. Feeding-preference and feeding-deterrence of the termite were assessed in the two-choice feeding tests using paper discs permeated with each fraction. The diethyl ether extracts of the non-steamed larch wood showed the feeding-deterrence activity. Taxifolin, the main component of these extracts, was found to be the major feeding-deterrence constituent. In the case of the steamed larch wood, taxifolin was not detected in any fractions, and the residual water-soluble fraction showed the feeding-preference activity. Furthermore, it was found that the feeding-preference constituents were contained in the coloring substances adsorbed by the Amberlite XAD-2 resin. From these results, the degradation of taxifolin and the formation of coloring substances during the steam treatment were to be considered as important factors of the attraction of steamed larch wood to the termite.