Efficacy of Essential Oils of Ocimum gratissimum and Mesosphaerum suaveolens Against Culex Quinquefasciatus

Abstract

Background Insecticide resistance is a prevailing global concern mandating the search for alternative control intervention and adopting innovative approaches such as insecticide coated curtains, insecticide-incorporated paints and the possibility of adulticidal trials using the ready-to-use humidifier. Objectives This study critically tested the larvicidal, pupicidal and adulticidal validity of the two plant essential oils, African basil ( Ocimum gratissimum) and pignut leave ( Mesosphaerum suaveolens) on Cx. quinquefasciatus Methodology Twenty, third instar larvae and pupae of Cx. quinquefasciatus were introduced into vials containing 1 ml and 0.5 ml of the essential oil in100 ml, 250 ml and 500 ml of water to form 0.01%, 0.001%, 0.002% 0.004% and 0.005% concentrations respectively. The exposure was done in triplicates. Mortality readings were taken at intervals of 10, 15, 20, 30, 40, 50, and 60 min adhering strictly to the WHO standard protocols. The highest concentrations, 0.01% (1 ml:100 ml) and 0.005% (0.5 ml:100 ml), were tried on adult mosquitoes in a 200 cm squared cage using ready-to-use humidifier. Results Mean mortality was highest in larvae exposed to O. gratissimum. Pupicidal activities of O. gratissimum oil was higher than M. suaveolens. Adult mosquitoes exposed to 0.005% of both plant oils caused highest mortality. The differences between the mean mortalities were significant (p < .05). Lethal Concentration (LC50 and LC95) of O. gratissimum and M. suaveolens exposed to larvae were 0.011 and 0.021%, and 0.024 and 0.042% respectively. Similarly, for pupicidal exposure, LC50 and LC95 were 0.019 and 0.041%, and 0.041 and 0.072% respectively. O. gratissimum oil was more efficacious especially for larval control. Conclusion Adulticidal efficacy of the essential oils can be enhanced through anticipated efforts towards emulsifying and synergizing them with other plant oils.