Southern pine wafers and Douglas-fir cubes pressure treated with copper naphthenate in AWPA P9 Type A oil or in toluene were evaluated for resistance to attack by the Formosan subterranean termite, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae). Wood samples were pressure treated to target copper retentions of 0.040, 0.075, 0.095, or 0.150 pcf, conditioned to simulate field exposure, and exposed to termites in 4-week no-choice and two-choice laboratory tests. Copper retentions were assayed by X-ray fluorescence after treatment, after leaching, and again after exposure to the termites. An approximate 20% loss of copper after weathering and termite exposure was noted in samples treated to target retentions of 0.095 and 0.150 pcf Cu. With or without a heavy oil carrier, copper naphthenate showed some toxicity to termites and deterred termites from feeding on the treated wood. At the highest target retentions of 0.095 and 0.150 pcf Cu, wood weight losses from termite feeding did not exceed 4% in no-choice tests or 1% in two-choice tests. Field data are needed, but these results indicate that copper naphthenate pressure treatments are of value in protecting wood from attack by the Formosan subterranean termite.

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