umigant Acute Toxicity of Rosemary and Lavender Essential Oils and a Synergism between them Against Adults of Callosobruchus maculatus (Col.: Chrysomelidaed) under Laboratory Conditions

 Cowpea weevil (Callosobruchus maculatus) is one of the key pests in the grain storage warehouses, which feeds on a variety of crops, including cowpea, pea, lentil, mung bean, and bean and causes damage on them. Sometimes this pest could destroy 100% of the stored bean seeds within 5-6 months. Currently, fumigants pesticide are used to control of cowpea weevil. This kind of control method has different adverse effects for consumers and does not provide effective control on the target pest. In order to control this pest in recent years, environmentally friendly pesticides, especially of plant origin are considered by researchers. In this regard, the pesticide effects of the rosemary essential oils (Rosmarinus officinalis L.) and lavender (Lavandula angustifolia Mill.) and their synergistic effects on the adults of Callosobruchus maculatus were studied.

 Bean beetles of this study were provided from Plant, Pest and Disease Research Institute in Karaj and then were transferred to laboratory of entomology of plant protection department of Jahad Keshavazi, Gom, Iran. The provided bean beetles were reared in laboratory condition to get mass production. Bioassay experiments of essential oils were performed with concentrations of 12, 25, 45, 86, 166, and 320 microliters per liter of air on adults of Callosobruchus maculatus (1-3 days) in 27±1°C temperature, 65±5% relative humidity and a photoperiod of 16 hours of darkness and 8 hours of light. The experiments were done on a mixture of mung bean and cowpea seeds into 60 ml glass containers in incubators. LC50 and LC90 index of each of the essential oils were calculated by POLO-PC software and analysis of variance was performed using SAS 9.1 software.

 The results indicated rosemary and lavender essential oils had insecticidal effect on the bean beetle and the insect mortality rate increased with increasing concentration. Rosemary essential oil was more toxic than lavender essential oil. The LC50 values of rosemary and lavender were 17.39 and 40.39 microliters per liter of air, respectively. To investigate the interaction effect of these two essential oils, another experiment was performed at previous concentrations in equal proportions (1: 1) of each essential oil and the LC50 value of the mixture was obtained 15.84 microliters per liter of air.

 The synergistic ratio (SR) of lavender and rosemary essential oils was the equal to 1.82, which indicates that these essential oils intensify the effect of each other. The mean mortality due to respiratory toxicity of lavender and rosemary and their mixtures were 61.29, 77.38 and 81.58%, respectively.