Fumigant toxicities of essential oils and two monoterpenes against potato tuber moth (Phthorimaea operculella Zeller)
Introduction: The potato tuber moth (PTM) is the major economic pest of potato. Different approaches were tried to prevent and control this pest including natural pesticides and synthetic fumigants. Objectives: This study was conducted to evaluate the insecticidal activity of the essential oils of thyme and myrtle. In addition to evaluating the insecticidal activity of carvacrol and eucalyptol against the different life stages of potato tuber moth using a fumigation bioassays. Methods: Thyme and myrtle oils were extracted from wild Thymus syriacus Boiss. and wild Myrtus communis L. by hydrodistillation. Fumigation experiments were conducted on potato tuber moth of different stages of development (eggs, larvae, pupae, and adults), using standard methods. The potato tuber moth was treated for different periods using different concentrations of the essential oils. One-way analysis of variance (ANOVA) was applied on the mortality percentages data to estimate the significance of differences between treatments at p<0.05. Probit analysis was used to estimate the LC50, LC90 and LT50. Results: Adult stage was the most sensitive to essential oils vapours with LC50 value of 0.5 μl/l air. Whereas, pupal stages were the most tolerant. The essential oil of thyme possessed the strongest fumigant toxicity against eggs with a LC50 value of 6.1 μl/l air. The two monoterpens showed varied fumigant toxicity against adult stage. Carvacrol achieved 100% mortality at 0.125 μl/l air after 6 h, and 0.025 μl/l air after 48h exposure with LT50 period of 0.5 h. Conclusion: The present work demonstrated that T. syriacus essential oil is a promising natural fumigant against the different developmental stages of PTM.