Insecticidal activity of essential oils derived from lavander, laurel and peppermint against lesser grain borer, Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae)

In this study, fumigant and repellent effects of the essential oils obtained from Laurus nobilis L. (Lauraceae), Mentha piperita L. and Lavandula x intermedia Emeric ex Loisel (Lamiaceae) plants against the lesser grain borer [Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae)], an important pest species of stored grains, were tested. The experiments were carried out in climate rooms at 27±1°C temperature, 50±10% humidity and completely dark conditions. The fumigant effect of essential oils at 5 different application concentrations (1, 5, 20, 50 and 200 μl/L air) against the larva, pupa and adult stage of R. dominica were tested. The highest fumigant effect against R. dominica larvae by 100% mortality was found to be at 200μl/L concentration of L. nobilis essential oil. For the adults, a concentration of 200μl/L of both L. nobilis and M. piperita essential oil caused 100% mortality. However, the complete mortality of pupal stage was not obtained and the highest mortality was determined as 49% in L. nobilis. Two different methods were used including petri dish bioassay and box bioassay in repellency bioassay. Filter paper was treated with each concentration (0.038, 0.192 and 0.769 μl/cm2) in petri dishes bioassay. Three concentrations of the essential oil were used in the box experiment (8.33, 41.67, and 166.67 μl/L). The repellent effects of both methods were determined in 1, 3, 6 and 24-hour period. In both experimental methods, the highest repellent effect was observed in M. piperita essential oil, while the least repellent effect was detected in L. intermedia essential oil. The effects of essential oils on germination of wheat seeds were also determined in the study. No adverse effects were observed for concentrations of tested essential oil for 48 hours of exposure. As a result of this study, it is thought that L. nobilis and M. piperita essential oil can be used as an effective bio-fumigant and repellent against stored product pests respectively. KEYWORDS: Rhyzopertha dominica, Mentha piperita L., Laurus nobilis L., Lavandula intermedia x Emerica x Loisel, fumigant, essential oil