Ocimum tenuiflorum oil, a potential insecticide against rice weevil with anti-acetylcholinesterase activity

Abstract

Essential oils are complex secondary metabolites, rich in volatiles, possessing a wide range of biological activities. In recent years, its application as bio-pesticide is receiving renewed attention due to its effective and safe application. In the present study, holy basil (Ocimum tenuiflorum) essential oil was tested for its insecticidal activity against Sitophilus orzyae (L.), using direct contact application and fumigation procedures. The GC–MS analysis of the O. tenuiflorum essential oil was also performed to characterize the essential oil. The GC–MS results showed that the major components present in O. tenuiflorum oil were eugenol and caryophyllene constituting about 70.5% of the total essential oil composition. Fumigant toxicity of essential oil and eugenol standard was assessed at different rates (100-1000 μL/L air) in space fumigation study. Toxicity results revealed that fumigant and contact toxicity of the oils was significantly (p < 0.05) influenced by concentration and exposure time. In contact toxicity assay, O. tenuiflorum essential oil showed the LC50 value of 0.376 μL/cm2 and maximum mortality at 0.786 μL/cm2 concentration after 24 h exposure. In fumigant toxicity assay, O. tenuiflorum essential oil and eugenol showed the LC50 value of 963.3 and 1070.6 μL/L, respectively at 6 h exposure. The O. tenuiflorum essential oil and eugenol was also evaluated for acetylcholinesterase activity in-vivo and was found to affect the acetylcholinesterase activity. The O. tenuiflorum essential oil exhibited insecticidal activity via inhibiting acetylcholinesterase activity and thus can be explored for its application as a possible botanical insecticide.