Biological activity of essential oils of Calocedrus decurrens and Cupressus arizonica on Lymantria dispar larvae and Phytophthora root pathogens

Composition of Calocedrus decurrens and Cupressus arizonica essential oils (CDEO and CAEO, respectively), their antifeedant activity on spongy moth (Lymantria dispar) larvae, as well as their antimicrobial activity on three Phytophthora species were investigated. In leaves of these two conifers from the Cupressaceae family, monoterpenes strongly dominated (90.5 and 85.0%, respectively), but their terpene profiles were different. The dominant compound of CDEO was δ-3-carene (49.5%), followed by myrcene (9.4%), terpinolene (8.6%) and α-pinene (7.0%). In CAEO, the most dominant compounds were limonene (23.3%) and α-pinene (20.5%), followed by umbellulone (12.0%) and terpinen-4-ol (9.5%). CDEO showed a strong antifeedant activity, while leaf discs treated with CAEO had phagostimulatory effect on spongy moth larvae. CAEO had no significant effect on relative consumption and larval growth rate, while CDEO reduced consumption and stimulated growth at the lowest EO concentration (0.05%). Both EOs significantly affected the growth of colonies of the Phytophthora species tested. At concentrations of 0.5% and 1%, a 100% inhibition was observed in almost all experimental groups, with the exception of P. plurivora on 0.5% CDEO. At a concentration of 0.1% inhibition rate varied from 15% in P. ×cambivora treated with CDEO to 90% in P. quercina treated with CAEO. These findings indicate that these two EOs could be used to control tree pests.