Resistance of timber to termite attack and the efficacy of two botanicals and wood ash in their protection

Abstract

Different tree species have different susceptibility to termite attack. Ten tree species commonly used in Kenya as a source of timber were exposed to termites with a view to investigating their natural resistance to this wood eating pest. Seven indigenous tree species were used namely , Milicia excelsa, Juniperus procera, Afzelia quanzensis, Podocarpus gracilior, Newtonia buchananii, Vitex keniensis and Ocotea usambarensis. The exotic tree species used were Casuarina cunninghamiana, Cupressus lusitanica and Grevillea robusta. In addition Melia volkensii extract, Ocimum sp. powder, wood ash and a mixture of wood ash and Ocimum sp. powder long considered to have insecticidal properties were added to these blocks of wood to test their preservative efficacy. Using 15% alcohol (ethanol), three concentrations were prepared from tlie M. volkensii crude extract. These were 1%, 0.5 % and 0.05%. The wood blocks were treated using these concentrations. In the case of Ocimum sp. powder, wood ash and the mixture of wood ash and Ocim,um sp. powder, 5gms, 3gms and 19m were used to treat the wood blocks. The graveyard technique was used while placing the wood blocks in the various experimental plots. Sampling was carried out after every two weeks. Damage done to the wood blocks by the termites was assessed using the ordinal scale of 0, 1, 2, 3 and 4. The experiments were carried out between January and June 1994. Wood blocks of different texture (rough and smooth) were used in these experiments. They were exposed in the field for periods ranging from two weeks to fourteen weeks. Xll The results indicate that M. excelsa, I. procera and A. quanzensis are more resistant to termite attack compared to the other tree species. These tree species are indigenous in Kenya and are therefore resistant to the local termites. Nevertheless, the two natural products and the wood ash had no significant effect on the feeding behaviour of termites. The rate of attack of the treated wood was the same as that of the untreated. The present studies revealed that there was no correlation between termite attack and duration of exposure. The attack may occur within a very short time or after a long time depending on the environmental conditions. The results also showed that termites preferred feeding on rough surfaces when provided with wood of different texture.