Laboratory evaluation of essential oil constituents against the termites, Acistrotermes latinotus

Abstract

In continuous search for alternative insecticides to combat potential problem of termite infestation in household and tree plantations; the bioactivity of the essential oils extracted by hydro distillation of leaves of Ocimum gratissimum, Gongronema latifolium and Piper guineensis was assessed under laboratory conditions at 20+30C, 70-75% R.H. and 12: 12h light: dark regimes for its biological activity against workers of the termites with Chlorpyrifos insecticide as a standard check. The botanicals were extracted using a Soxhlet extractor and serially diluted at different concentrations of 0.125%, 0.25% and 0.50% including 0% as the control. The essential oils at 0.25ml of the different concentrations of the botanicals and insecticide were applied using a syringe on twelve adult workers of termites in each Petri dishes. Mortality count or number of the termites knocked down after thirty, sixty, ninety and one hundred and twenty minutes respectively during the trial was recorded and expressed in percentages. The individual components of the essential oil were identified through GC, GC-MS and GC-Co injection with authentic standards. The identity of a total of 17 constituent compounds of the essential oil of each plant was confirmed and their relative proportion determined. The major compounds identified among the botanicals and the insecticide in their relative proportion included Alpha Pinene, Quinoline, 3-methyl and Benzylisoquinoline. Only Alpha Pinene was found in O. gratissimum and Chlorpyrifos insecticide, while Quinoline, 3 methyl and Benzylisoquinoline were recorded in the botanicals including the insecticide. The major components were found to be largely responsible for the toxic action of its essential oil against the termites. The highest dosage of the essential oils of the plant materials tested induced the highest mortality in the termites after 120 minutes. Within `120 minutes, O. gratissimum (55%) P. guineensis oil (52%) was significantly more effective than G. latifolium (47%) at the bioactive concentration of 0.25mg/L while Chlorpyrifos insecticide recorded the highest termite mortality. The termite mortality increased gradually with the increase in essential oil concentrations and with the time of exposure. There is need to diversify the use of botanicals especially in the agricultural pest management sector.