Toxicity of monoterpenoids and other natural products to the formosan subterranean termite (Isoptera: Rhinotermitidae)

Monoterpenoids are potentially useful for the development of new insecticides because of their low mammalian toxicity. Different monoterpenoids differ significantly in their toxicity to particular insects. We evaluated the toxicity of 6 monoterpenoids, 2 alkaloids, and 1 hydrocarbon that are plant or ant semiochemicals to the Formosan subterranean termite, Coptotermes formosanus Shiraki. Bioassays were performed to determine the effects of the semiochemicals on the mortality and tunneling behavior of termites and the fumigant activity of 3 monoterpenoids?, citral, geraniol, and eugenol. We also tested the effect of the monoterpenoid alcohol eugenol, as a feeding deterrent. We found significant differences in the termiticidal activity of the different compounds tested. Monoterpenoid alcohols, particularly eugenol, were the most effective as termiticides against C. formosanus. Eugenol was also more effective as a fumigant than citral and geraniol. In addition, termites did not tunnel through eugenol and geraniol-treated sand barriers for at least 5 d. However, eugenol was not effective as a feeding deterrent when applied directly to blocks of wood, except at the relatively high concentration of 100,000 ppm.