Chemical composition, toxicity and physiological effects of thyme oil and its two components on mulberry pyralid moth

Abstract Thymus vulgaris is a plant with known insecticidal properties. In order to explore its use in the control of the mulberry snout moth, the essential oil this plant and two of its major components, thymol and carvacrol, were evaluated in laboratory bioassays. GC-MS analysis of the oil depicted thymol (26.9%) and carvacrol (5.7%) as the major constituents. The estimated LD50 values for thyme essential oil, thymol and carvacrol were 2.82, 32.18 and 56.54 µg/larva, respectively. However, the thyme essential oil was more toxic than its two main compounds.The activity of certain detoxifying enzymes such as α- and β-esterase, glutathione S-transferase and cytochrome P450 were significantly inhibited in thymol-treated larvae compared to the control group. Similarly, the activity of alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase and alkaline phosphatases enzymes in thymol-treated larvae decreased while the activity of acid phosphatases increased. Our results suggest that thyme essential oil and its components have potential for the control of G. pyloalis larvae in mulberry orchards, where no synthetic chemicals are allowed.