α-Spinasterol, temperature and moisture content as determining factors in the infestation of Camellia sinensis by Xyleborus fornicatus

Abstract

Analyses of segments of clones of tea bushes, growing in different climatic conditions, indicated that temperature, moisture content, the amount of available α-spinasterol, and saponin level determined the degree of infestation by the shot-hole borer beetle pest, Xyleborus fornicatus. The principal factors affecting α-spinasterol availability were the concentration of the sterol per se, and the levels of saponins, theanine, arginine, calcium and chebulagic acid. It is proposed that α-spinasterol is converted by X. fornicatus to moulting hormones required for pupation of the beetle larvae, and that this sterol is also necessary for spore formation by the ambrosia fungus, Monacrosporium ambrosium, which is associated with the female adult beetle; tea saponins are inhibitory to the development of both the ambrosia fungus and X. fornicatus. The distribution of amino acids, fiavanols and other polyphenols, saponins, α-spinasterol, α-spinasterol glycoside, β-amyrin epi-friedelinol, friedelin and oleanolic acid throughout the tea bush, at periods of 6–40 months after pruning, is described.