Fumigant toxicity of essential oils from three lamiaceous plants and methyl iodide against Phthorimaea operculella (zeller) (Lep.: Gelechiidae)

Abstract

The potato tuberworm, Phthorimaea operculella (Zeller), is a major pest that courses economic losses of potato Solanum tuberosum L. in both the field and the stores. In this research, the fumigant toxicity of essential oils of three Lamiaceous plants including Thymus caucasicus L., Rosmarinus officinalis L. and Satureja hortensis L. and methyl iodide (a chemical fumigant) were evaluated on P. operculella and on its demographic parameters under the laboratory conditions. Essential oils were extracted through hydro-distillation method using a Clevenger-type apparatus. The gas chromatography-mass spectroscopy (GC-MS) analysis indicated that thymol (29.76 %) in T. caucasicus, carvacrol (36.67 %) in S. hortensis and 1, 8-cineole (26.94 %) in R. officinalis essential oils were the major secondary constituents. The 50 % Lethal Concentration (LC50) values for T. caucasicus, R. officinalis, and S. hortensis essential oils as well as methyl iodide towards P. operculella eggs were 5.99, 4.58, 3.55 and 0.29 µL L− 1 air, respectively. On the other hand, methyl iodide showed the highest acute toxicity on the egg stage of P. operculella compared to the essential oils. The 30 % Lethal Concentration (LC30) values of T. caucasicus, R. officinalis, and S. hortensis essential oils and methyl iodide (4.12, 3.53, 1.96, and 0.23 µL L− 1 air, respectively) were affected the life history and demographical parameters of P. operculella. The longest development time was observed on methyl iodide and the shortest was on T. caucasicus and S. hortensis essential oils. The intrinsic rate of natural increase (rm) values obtained in the control group and treated insects were: 0.19, 0.16, 0.14, 0.13, and 0.01 female progenies per female per day for T. caucasicus, S. hortensis, R. officinalis essential oils and methyl iodide, respectively. These results suggested that methyl iodide was significantly more toxic to the P. operculella compared to the essential oils of all the three mentioned plants. Meanwhile, it was concluded that the application of these plant essential oils can be useful as an alternative method for potato tuberworm control in storage facilities.