WOOD DESTROYING INSECTS AND THEIR ATTACK ON EIGHT COMMERCIAL TIMBER SPECIES IN SRI LANKA

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Wood destroying insects and their attack on eight commercial timber species were studied through a survey in different climatic zones in sri Lanka, field experiments and laboratory experiments. Eight commercial timber species used for this study are Jak (Artocarpus heterophyllus), Eucalypts (Eucalyptus grandis) , Rubber (Hevea brasiliensis), Tualang (Koompassia excelsa), Lunumidilla (Melia dubia), Pine (Pinus caribaea), Mahogany (Swietenia macrophylla) and Teak (Tectona grandis). Common wood destroying insects were collected and identified as Longhorn beetle (Batocera rubus), Powder - post beetle (Heterostrychus brunneus), Subterranean termite (Odontotermes redemanni), Carpenter ant (Camponotus abdominalis), carpenter bee (Xylocopa latipes), Pinhole borer and weevil. Subterranean termite, Powder - post beetle and Longhorn beetle were found as the most important insects according to their damage. Subterranean termite attack was studied in the field under natural condition using grave yard trials. Attacks of termite, powder post beetle and longhorn beetle were studied in laboratory experiments. These laboratory experiments were carried out according to the techniques developed by earlier authors, and using new techniques developed by the author. Ants and Cunningimella fungus were observed as a biological control for termites in the field as well as in the laboratory experiment. Results show that loss of weight due to insect attack was significant different between different timber species. Mortality of insects also significantly differ in different timber species. Based on these findings timber species were categorised into three groups: insect resistant species, moderately resistant species and susceptible species. Eucalyptus, teak and tualang were the most resistant species while freshly felled jak was highly susceptible to larvae of Batacera (Longhorn beetle). Mahogany was susceptible to powder - post beetle. Rubber was the most susceptible species, and it is recommended to use preservative treatment for the effective utilization af these species. Wood parameters, density and moisture content of wood were determined under air dried condition. Moisture content of wood was positively correlated to the termite attack and the density was negatively corre·lated to the termite attack.