In the current study, the larvicidal activity of leaf essential oils from three eucalyptus species (Eucalyptus largiflorens Meull, Eucalyptus oleosa Meull, and Eucalyptus spathulata Hook) against American white moth, Hyphantria cunea Drury 1773 (Lepidoptera: Arctiidae), was investigated. Mortality was recorded daily for three days after treatment. Leaf disc bioassays revealed that all three oils had strong insecticidal activity on the experimental insects insofar as 50% lethal concentrations (LC 50 ) for E. oleosa, E. spathulata, and E. largiflorens at 24 h exposure time were 0.36, 0.61, and 1.24%, respectively. The time needed to kill 50% (LT 50 ) values were calculated as 9.09 h with E. largiflorens, 11.03 h with E. oleosa, and 13.03 h with E. spathulata at the highest concentrations (2.5% for E. largiflorens, 2% for E. oleosa, and 2.5% for E. spathulata). Based on probit analysis, an increase in the susceptibility of the insect was associated with an increase in the different concentrations of all oils and the increase in the time of exposure. The results of this study show that leaf essential oils of E. largiflorens, E. oleosa, and E. spathulata might be considered as a potent source for the production of fine natural larvicides.

− Colorado potato beetle is a most destructive insect pest of potato throughout the world. Although utilization of chemical insecticides is a main method for management of this pest, their negative side-effects such as threat to humans and the environmental pollution prompted researchers to search for natural alternatives. Recently plant essential oils with low or without side-effects against noun-targeted organisms and with high availability were considered as safe bio-pesticides. In the present study, toxicity of essential oil of Iranian lemongrass, Cymbopogon citratus Stapf, was evaluated against 3th instar larvae and adults of Colorado potato beetle by a leaf dipping method. Results displayed essential oil had notable toxicity against both larvae and adults after 24 and 48 h exposure times. Probit analysis revealed LC 50 values (lethal concentration to kill 50% of population) with 95% confidence limits were 10.32 (9.17 -11.72) and 7.76 (6.80 -8.74) µl/ml for larvae and 6.27 (4.82 -8.15) and 4.35 (3.24 -5.62) µl/ml for adults after 24 and 48 h, respectively. Based on regression analysis, a positive correlation between log concentration of essential oil and insect mortality was achieved. Results indicated C. citratus essential oil can be candidate as a natural alternative to the harmful chemical insecticides in the management of Colorado potato beetle.