Use of a short span field test to evaluate termite resistance of Eucalyptus grandis and Bobgunnia madagascariensis in a tropical environment

Abstract

Despite being treated with preservatives, the service life of transmission poles and fence posts in the Zambian Copperbelt province is close to fifteen years. However, the service life is only two years for untreated timber, mainly due to termite damage. This short service life is exerting more pressure on an already over-burdened timber resource base. This study used an accelerated field test investigation to facilitate initial assessment of several lesser known indigenous timbers for their termite resistance properties. To determine the service life and natural durability of Eucalyptus grandis and Bobgunnia madagascariensis to termite attack, samples of each wood species were field exposed to an aggressive species of subterranean termites for 32 days. Morphological and genetic analyses confirmed that the aggressive species of termites in this study was Coptotermes formosanus, commonly referred to as Formosan subterranean termites. Results indicated that E. grandis can be labeled as susceptible (S) following the standard natural durability rating procedure on the basis of service life projected from short term field exposure weight loss determination. Using short duration exposure weight loss and visual designation, similar to the Gulfport scale, B. madagascariensis was designated as very durable (D). These results showed that natural durability of timber against termites can be estimated after a short duration field exposure to Formosan subterranean termites. This method offers a fast field test for screening of promising lesser known tropical timbers.