Title: Eco-friendly alternative malaria control strategies: Insecticidal activity of Aeollanthus pubescens leaf essential oil against Anopheles gambiae

Abstract

Background: The excessive use of synthetic insecticides is responsible for many cases of resistance in insects. Therefore, the use of natural molecules of ecological interest with insecticidal properties turns out to be an alternative approach to the use of synthetic insecticides. This study aims at investigating the larvicidal, adulticidal activity and the chemical composition of the essential oil of Aeollanthus pubescens on the major malaria vector, Anopheles gambiae. Methods: Three reference strains of Anopheles gambiae sensu stricto (Kisumu, Kiskdr and Acerkis) were used in this study. The leaves of A. pubescens were collected in southern Benin. The standard WHO guidelines for larvicide evaluation were used and the chemical composition of the essential oil was analysed by gas chromatography coupled to mass spectrometry. Adult mosquitoes were exposed to the net pieces coated with the essential oil for 3 min using the WHO cone bioassay method. Probit regression analysis was used to determine lethal concentrations (LC50) and time to knockdown (KDT50). The Log-rank test was performed to evaluate the difference in survival between the strains. Results: 14 components were identified representing 98.3% of the total of oil content. The major components were carvacrol (51.1%), thymyle acetate (14.0%) and ɣ-terpinene (10.6%). The essential oil has shown larvicidal properties with LC50 of 29.6, 22.9, and 28.4 ppm respectively on Kisumu, Acerkis and Kiskdr strains. With the net pieces treated at 165 µg/cm2, the KDT50 of both Acerkis (1.71 s, Z =3.34, p < 0.001) and Kiskdr (2.67 s, Z =3.49, p < 0.001) individuals were significantly lower than that of Kisumu (3.8 s). The lifespan of the three mosquito strains decreased respectively to 1 day for Kisumu (χ2 = 99, df = 1, p < 0.001), 2 days for Acerkis (χ2 = 117, df = 1, p < 0.001) and 3 days for Kiskdr (χ2 = 96.9, df = 1, p < 0.001). Conclusion: Our findings show that the A. pubescens essential oil has a larvicide and adulticide properties against the malaria vector An. gambiae s.s. This bio-insecticidal activity may be a promising discovery for the control of the resistant malaria-transmitting vectors.