Lethal and sublethal effects of low temperature, alone and in combination with eucalyptus essential oil, against adult Mediterranean flour moth, Ephestia kuehniella

Low temperatures have significant effects on the biological aspects of stored-product pests; thus, those can be used as a control method. Due to the delayed effects of low temperatures, the lethal and sublethal effects of 4˚C temperature were investigated, alone and combined to the eucalyptus essential oil, on mortality and some reproductive aspects of Mediterranean flour moth, Ephestia kuehniella Zeller (Lep.: Pyralidae) for probable elimination of this limitation.

All experiments were carried out at the Entomological Research Lab., Department of Plant Protection, Gorgan University of Agricultural Sciences and Natural Resources. The insect reared on wheat flour under laboratory conditions (25 ± 2 °C, 70 ± 5% R.H., 16:8 L:D). Adult's mortality due to the continuous exposure to low temperature, the effects of adults exposure to low temperature on their longevity, fecundity and percentage egg hatch, and finally, the effects of low temperature combined to different concentrations of eucalyptus essential oil on mortality, daily oviposition and percentage egg hatch of survived adults were recorded, and synergistic or antagonistic effects were determined. The chemical composition of essential oil was analyzed using a Varian CP-3800 gas chromatograph equipped with a Varian Saturn 2200 ion trap mass spectrometer and Helium as the carrier gas.

Continuous exposure to low temperature prolonged the lifespan of adult insects (some of them lived more than 33 days). Estimated LT50 and LT95 values for male adults of the Mediterranean flour moth exposed to 4 °C were 14.87 and 45.17 days, respectively; for female adults were 10.77 and 39.38 days, respectively; and as total were 12.67 and 42.28 days, respectively. Adult exposure to low temperature decreased the longevity, fecundity and percentage of the egg hatch of survived ones. By increasing exposure interval and essential oil concentration, fecundity decreased at a higher rate but percentage egg hatch did not affect. The interactions between low temperature and different plant essential oil concentrations were antagonistic. Among 16 identified constituents in the eucalyptus essential oil, 1,8-cineol (Eucalyptol) was the major oil component (30.48%).

Long-time exposure of stored-products moths to 4˚C temperature reduces the activity and mobility of these pests which has negative effects on their reproductive aspects. Hence, it could be effective as a control method. Antagonistic effect between low temperature and plant essential oil indicates that before selecting two insecticide agents for using in the combination, it is necessary that their synergistic interaction would be confirmed by carrying out the appropriate experiments.