Abstract• Tree age is one of the most important factors to affect the natural durability of wood.• The purpose of this study was to determine the natural termite resistance of heartwood and sapwood of teak (Tectona grandis Linn. fil.) for trees aged 8, 30 and 51 years. Reticulitermes speratus Kolbe was employed as a test termite using a no-choice feeding method.• The heartwood and sapwood of all of the trees tested exhibited antitermitic activity. Based on the mean mass loss due to termite activity, the sapwood and heartwood regions of 8-year-old trees are the most susceptible to termites while the heartwood regions of the 30-year-old trees showed termite resistance similar to the termite resistance of 51-year-old trees.• The mass loss is moderately correlated with n-hexane extractive content, total extractive content, brightness and redness of the wood.

Abstract• Quinones are primarily responsible for the natural durability of teak.• The previous paper in this series reported on the natural termite resistance of teak trees of different ages (8-, 30-and 51-year-old trees). In this study, the radial distribution of quinones (tectoquinone, lapachol, desoxylapachol and its isomer) and other components in the ethanol-benzene (1:2) extract were measured by means of gas chromatography.• Significant differences in desoxylapachol or its isomer content were found among the outer heartwood of 8-, 30-and 51-year old trees, as well as between the inner and outer parts of the heartwood.• All toxic quinone contents were positively correlated with the total extractive content. The highest correlation degree was measured in the isodesoxylapachol content.• Although linearly related, only modest correlations were observed between the natural termite resistance parameters and the content of tectoquinone and isodesoxylapachol. Mots-clés :Tectona grandis / extractibles / tectoquinone / desoxylapachol / âge des arbres Résumé -Distribution radiale des quinones dans du teak de plantation (Tectona grandis L.f.).• Les quinones sont à l'origine de la durabilité naturelle du teak.• Le précédant papier de la série traitait de la résistance naturelle contre les termites pour des arbres de 8,30 et 51 ans. Dans cette étude, la distribution radiale des quinones (tectoquinone, lapachol, deoxylapachol et son isomère) et des autres composés présents dans les extraits éthanol-benzène (1:2) est déterminée par chromatographie en phase gazeuse.• Le contenu en desoxylapachol ou ses isomères présente des différences significatives en périphérie du bois de coeur des arbres de 8, 30 et 51 ans de même qu'entre la partie interne et externe du bois de coeur.• Toutes les teneurs en quinones toxiques sont corrélées positivement avec le contenu total d'extractibles. Le degré de corrélation le plus élevé est mesuré pour la teneur en isodesoxylapachol.• Bien qu'il existe une relation linéaire entre les paramètres de résistance naturelle aux termites et la teneur en tectoquinone et isodesoxylapachol, les corrélations observées sont modestes.

Mechanical properties of sawn timber are the most important characteristics in many applications, particularly for structural timber. The previous paper in this series reported on the physical properties of teak trees at different sites (Panggang, Playen, Nglipar)