Fumigant toxicity of essential oils and pure compounds against Sitophilus oryzae L. (Coleoptera: Curculionidae)

In this study, Zingiber officinale (Zingiberaceae) and Piper cubeba (Piperaceae) essential oils and two pure natural terpenes, α-pinene and β-caryophyllene, were evaluated for their repellent, insecticidal and acetylcholinesterase enzyme inhibitory activities against rice weevil, Sitophilus oryzae . In the repellency assay, Zingiber officinale and Piper cubeba essential oils repelled S. oryzae adults significantly at 0.003125% while α-pinene and β-caryophyllene repelled S. oryzae adults significantly at 0.025% concentrations. Fumigation of S. oryzae adults with these essential oils and pure compounds caused lethality alone or in binary combinations. Median lethal concentrations (LC ₅₀) were 1.79, 1.07, 1.19, and 1.98 μl cm ⁻ ³ air for Z. officinale, P. cubeba essential oils, α-pinene and β-caryophyllene, respectively, against S. oryzae adults. In the case of Z. officinale + P. cubeba essential oils and α-pinene+β-caryophyllene combinations, LC ₅₀ values were 1.31, and 1.64 μl cm ⁻ ³, respectively, against S. oryzae adults. P. cubeba essential oil and α-pinene were more toxic than Z. officinale essential oil and β-caryophyllene. In binary combinations, essential oils and pure compounds did not exhibit significant synergism. Inhibition of acetylcholinesterase enzyme (AchE) activity was observed in S. oryzae adults when fumigated with sublethal concentrations of Z. officinale and P. cubeba essential oils, α-pinene and β-caryophyllene, alone or in binary combinations. These essential oils and pure compounds probably induce toxicity by inhibiting acetylcholinesterase enzyme activity.