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.
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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.
Citation
MSc.Publisher
School of Biological Sciences, University of Nairobi
Description
Master of Science Degree in the Department of Zoology