Resistance of borate-treated Douglas-fir to the Formosan subterranean termite

Toxicity of disodium octaborate tetrahydrate (DOT as TIM-BOR?) to Formosan subterranean termites and termite feeding on treated Douglas-fir heartwood were evaluated in laboratory and field tests. Feeding on filter papers impregnated with borate solutions reduced but did not eliminate termite gut protozoan populations. In a forced-feeding laboratory assay, Douglas-fir heartwood treated to retentions greater than or equal to 0.35 percent boric acid equivalents (BAE) drastically reduced termite feeding and resulted in 100 percent termite mortality within 3 weeks. Gradual and significant mortality (49%) after 4 weeks of feeding at 0.16 percent BAE suggests that this or lesser concentrations may be useful in baits for remedial termite control. After 162 days of field exposure to an active termite colony, moderate feeding was noted at 0.65 percent BAE (13.6% weight loss) and 0.73 percent BAE (16.9% weight loss), and only slight damage (2.5% weight loss) at the highest retention field-tested of 1.02 percent BAE. These results indicate that treatment with DOT provides protection from Formosan subterranean termite attack, but that some cosmetic damage occurs even at high retentions. This cosmetic damage is unlikely to create a structural hazard, but additional field evaluations are needed to determine whether borate treatments will provide protection to visible timbers that will be acceptable to the consumer.

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