The larvicidal potential of the essential oils from Origanum onites L. and O. minutiflorum (O. Schwarz & P. H. Davis) (Labiatae) and their commercially available components (carvacrol, thymol, γ-terpinene, and terpinen-4-ol) was investigated against the brown-tail moth, Euproctis chrysorrhoea (L.) (Lepidoptera: Lymantriidae), an important pest of agricultural and forest crops in southwestern Turkey. This pest is also a public health concern due to the urticating hairs of its larvae. The chemical composition of these essential oils was also determined by gas chromatography-mass spectrometry (GC-MS). Carvacrol was the major component of both O. onites and O. minutifulorum essential oil, at 29.6% and 56.1%, respectively. The oils and components were bioassayed against 4th instars of E. chrysorrhoea at concentrations ranging from 0.0625% to 0.50%. All materials tested showed larvicidal activities in a concentration-dependent manner. Topical applications of the essential oils from O. onites and O. minutiflorum applied at 80 µl of solution per larva were highly toxic, with LC50 values of 522 and 1076 ppm, respectively. Of the four commercial components tested, thymol and carvacrol were the most active (LC50 = 367 and 424 ppm, respectively). The other two components, γ-terpinene and terpinen-4-ol, were also toxic with LC50 values of 1172 and 2126 ppm, respectively. Our overall results suggest that the essential oils from O. onites and O. minutiflorum and their components may be potential alternatives to synthetic insecticides for the control of brown-tail moth larvae.
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