Characterization and biocidal activity of some yellow-cedar heartwood compounds

The essential oil from yellow-cedar heartwood and its constituent compounds were investigated for their ability to control arthropods of public health concern and forest microbial pathogens. Comparisons were made for the activities of the essential oil, isolated compounds, and derivatives against mosquitoes (Aedes aegypti), ticks (Ixodes scapularis), fleas (Xenopsylla cheopis), and the microbe responsible for Sudden Oak Death (Phytophthora ramorum). Laboratory bioassays showed that nootkatin and carvacrol are strong inhibitors of P. ramorum zoospore and sporangia germination and hyphal growth. Zoospore germination was reduced to 0% with 10 ppm of nootkatin, or 100 ppm carvacrol. Nootkatin instantaneously destroys the membrane surrounding zoospores and sporangia, but not the hyphae. Biocidal assays against arthropods showed that nootkatone, valencene-13-ol, and carvacrol were the most effective, while nootkatin was not effective. Nootkatone was the most effective against ticks (LC₅₀ = 0.0029%) and valencene-13-ol the most effective against mosquitoes (LC₅₀ = 0.0024%). Carvacrol showed activity against ticks, fleas, and mosquitoes with LC₅₀ values after 24 hours at concentrations of 0.0068, 0.0059, and 0.0051% (wt:vol), respectively. Residual activities were good for nootkatone and valencene-13-ol for up to four weeks. Repellency of yellow-cedar compounds against ticks compared to DEET showed that nootkatone and valencene-13-ol had repellent concentration (RC₅₀) values of 0.0458 and 0.0712% (wt:vol), respectively, compared to DEET (RC₅₀ = 0.0728%).