Effects of caffeine and a tea flavanoid on Monacrosporium ambrosium, ectosymbiote of shot-hole borer beetle of tea

Abstract

Shot-hole borer (SHB) beetle Euwallacea fornicatus (Xyleborus fornicatus) Eichh. (Coleoptera: Scolytidae) is the most serious insect pest of tea (Camellia sinensis L.) plantations in Sri Lanka. Caffeine, the major alkaloid found in tea, inhibits the growth of both Monacrosporium ambrosium, ectosymbiote of SHB and the SHB beetle, in laboratory culture media 1,2 . Caffeine contents of two tea cultivars that are resistant (TRI 2023) and susceptible (TRI 2025) to SHB infestation 3 , indicated that there was an increase in caffeine content after SHB infestation of both tea cultivars, the increase being higher in the more susceptible tea cultivar 4 . However, the two organisms are able to develop within tea stems that have a caffeine concentration which is higher than the concentration that inhibited the development of M. ambrosium and SHB beetles in laboratory culture media. Flavan-3-ols and their gallate esters (catechins) may constitute up to 30% of young tea shoots. Epigallocatechin gallate (EGCG), the major phenolic compound found in tea, constitutes 9-13 % of the dry weight of young tea shoots 5 . The present study was carried out to determine whether EGCG modulates the effect of caffeine on M. ambrosium in laboratory culture media. The effect of caffeine and EGCG on M. ambrosium was studied by determining the fungal colony diameter, sporulation and spore germination on solid agar media and mycelial mass in liquid culture media respectively, into which varying amounts of these two phytochemicals were incorporated. The ambrosia fungus was isolated 1 from a surface sterilized adult female SHB removed from a gallery in a tea stem. The eight types of media (1-8), were prepared 2 in Cook’s 2 quarter strength agar