Comparative Study of Insecticides Formulated from Essential Oils with Two Commercial Insecticides

Abstract

The insecticidal activities of four formulated insecticides of plant essential oils (EOs) origin were compared with two synthetic insecticides against cowpea seed bruchid, Callosobruchus maculatus. The pesticide residues from the application of the synthetic pesticides were also investigated. The essential oils were extracted by steam distillation. The essential oil-based insecticides were formulated by mixing 0.25 g of the oil in 5 g of either calcium carbonate or clay (carrier). The various insecticides were extracted from treated cowpea seeds with dichloromethane and then clean in a column with n-hexane and analysed on auto system Gas Chromatograph (GC) with electron capture detector (ECD). The chemical composition of the oil was analysed by Gas Chromatograph-Mass Spectrometer (GC-MS). The result of the contact activities of the various insecticides against cowpea bruchid (Callosobruchus maculatus) showed that all insecticides produced 100% knockdown of Callosobruchus maculatus twelve hours after its formulation. The least effective EO-formulated insecticides was those of African nutmeg (Monodora myristica) having 90% activity after 24 hours. Aluminium phosphide and permethrin recorded twenty-one and twenty pesticides residues, respectively, while the essential oil formulated insecticides did not record any pesticide residue. Aluminium phosphide had fifteen of the residues detected above the Maximum Residual limits set by FAO/WHO, while permethrin had 13 of the pesticide’s residue above the MRL. The result obtained showed that the insecticides formulated from the four essential oils have high insecticidal activity, with no record of any pesticides residues. Hence, they demonstrated potential suitability as eco-friendly biopesticides.