Natural resistance of Alaska-cedar, redwood, and teak to Formosan subterranean termites
1994
Grace, J.K. | Yamamoto, R.T.
The relative susceptibility of Alaska-cedar (Chamaecyparis nootkatensis), redwood (Sequoia sempervirens), southern pine (Pinus spp.). and Douglas-fir (Pseudotsuga menziesii) heartwood to feeding by the Formosan subterranean termite (Coptotermes formosanus) was evaluated in 4-week no-choice and two-choice laboratory tests. Termites fed equally on pine and Douglas-fir, and significantly less (at least 50% less) on Alaska-cedar and redwood. Within-species variability in susceptibility, suggesting variability in heartwood extractive content, was apparent with both Alaska-cedar and redwood. Reduced feeding was accompanied by high termite mortality, indicating that the heartwood extractives of both species are toxic to termites. In choice tests, termites avoided feeding on either Alaska-cedar or redwood if Douglas-fir was also present. When presented with a choice of either Alaska-cedar or redwood, termites fed significantly less on Alaska-cedar. The susceptibility of teak (Tectona grandis) to termite attack, in comparison to treated (ammoniacal copper zinc arsenate, chromated copper arsenate, or disodium octaborate tetrahydrate) and untreated Douglas-fir, was also evaluated in a 6-week field exposure. In this test, there was no visible evidence of feeding on any of the teak samples. Our results indicate that these naturally durable woods compare favorably in termite resistance to preservative-treated wood.
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