A comparative evaluation of Origanum onites essential oil and its four major components as larvicides against the pine processionary moth, Thaumetopoea wilkinsoni Tams.

The pine processionary moth (PPM), Thaumetopoea wilkinsoni Tams. (Lepidoptera: Thaumatopoeidae), is an important forest pest in the Mediterranean area, and urticating hairs of the caterpillars of this species cause allergic reactions on skin of humans and animals. In the present study, the larvicidal activities of Turkish oregano (Origanum onites L.) essential oil and its four major components, carvacrol, gamma-terpinene, terpinen-4-ol and thymol, were evaluated against fourth/fifth-instar larvae of PPM under laboratory conditions. The essential oil was larvicidal to PPM with an LD50 value of 3800 mu L L-1 when 0.1 mL was applied per larva. Carvacrol was the most toxic component found in the essential oil (LD50 = 3100 mu L L-1), followed by thymol (LD50 = 5500 mu L L-1). The other two components, gamma-terpinene and terpinen-4-ol, were less effective. The results showed that Turkish oregano essential oil and its two components, carvacrol and thymol, could be potential alternatives to synthetic insecticides for the control of PPM. (c) 2007 Society of Chemical Industry.