INSECTICIDAL PROPERTY OF TERPENES AGAINST MAIZE WEEVIL, SITOPHILUS ZEAMAIS (MOTSCHULSKY)

Abstract

Synthetic pesticides are used indiscriminately in insect pest management, which damages the ozone layer and causes resistance in target organisms as well as neurotoxicity, carcinogenicity, teratogenicity and mutagenesis in non-target organisms. Due to these negative consequences, research is now focused on using plant-based techniques to control insect pests. The maize weevil, Sitophilus zeamais (Coleoptera: Curculionidae), was tested in the laboratory to determine the insecticidal effects of two pure essential oil constituents, namely α-pinene and β-caryophyllene. These two terpenes were tested against S. zeamais for their toxic, ovipositional, developmental, and feeding inhibitory effects. When S. zeamais adults were fumigated for 24 and 48hrs, the median lethal concentrations (LC50) of α-pinene and β-caryophyllene were 0.412 and 0.305 μlcm-3 and 0.486 and 0.315 μlcm-3 air respectively. When S. zeamais adults were exposed for 24 and 48hrs in a contact toxicity assay, the LC50 values for α-pinene and β-caryophyllene were 0.388 and 0.256 μlcm-2 and 0.308 and 0.216 μlcm-2 area respectively. Adults exposed to sub-lethal concentrations of both terpenes experienced decreased acetylcholine esterase (AChE) enzyme activity. In S. zeamais, α-pinene and β-caryophyllene decreased oviposition, progeny output and eating. According to this study, α-pinene and β-caryophyllene can be used to make environmentally acceptable formulations and as a substitute for synthetic insecticides.