Effect of Thymus and Rosemary essential oil on toxicity and physiological parameters of diamondback moth Plutella xylustella L.

The effects of two medicinal plants from Lamiaceae including: Thymus vulgaris L. and Rosmarinus officinalis L. on toxicity and physiological characteristics of diamond back moth Plutella xylustella L. were studied. Acute contact and oral toxicity on third instar larvae were estimated. The LC10، LC30 and LC50 for essential oil of Rosemary and Thymus were 0. 051، 0. 372، 1. 198 percent and 0. 0129، 0. 0638 and 0. 325 percent respectively. According to the results، the highest toxicity belonged to Thymus essential oil and the lowest to Rosemary. The repellency effect under sub lethal concentrations of LC10 and LC30 of essential oils on 3rd instar larvae of diamondback moth were investigated and they were 27. 2±4. 42، 40. 6±0. 31and 43. 72±3. 85، 56. 05±4. 51 percent for Rosemary and Thymus respectively. Relative consumption rate، efficiency of conversion of ingested food، efficiency of conversion of digested food، relative digestibility and relative growth rate of the treated larvae showed significant differences compared with the control. The effectiveness of plant essential oils on digestive enzymes، total protein، triglycerides، alkaline phosphatase، protease and alpha-amylase were reduced in treated larvae compared to control. However the activity of Glutathion-s-transferase was reduced under the effect of essential oils. Hence it is concluded that the essential oils used in the present experiment not only show larvicidal effect but could show considerable changes in repellency and feeding efficiency under the effect of sublethal concentrations.