Alternatives to chemical resistance: Combinations of Cymbopogon nardus and Ocimum americanum essential oils improve the bioefficiency control against the adults populations of Aedes aegypti L. (Diptera: Culicidae).

Abstract

Dengue vector control strategies are mostly based on chemicals use against Aedes aegypti populations. The current study aimed at investigating the insecticidal effects of essential oils obtained from five plant species, Cymbopogon citratus, Cymbopogon nardus, Eucalyptus camaldulensis, Lippia multiflora and Ocimum americanum, and combinations of Cymbopogon nardus and Ocimum americanum on Aedes aegypti populations from Bobo-Dioulasso. For this purpose, adults of the susceptible and field strains of Aedes aegypti were tested in WHO tubes with EO alone and binary combinations of O. americanum (OA) and C. nardus (CN) (scored from C1 to C9). The extraction of the essential oils was done by hydrodistillation and their components were determined by GC/MS. Among the 5 EOs tested, L. multiflora essential oil was the most efficient, with KDT50 values below 60 minutes on all Aedes aegypti strains tested, and also with a rate of mortality up to 100 and 85% for Bora Bora and Bobo-Dioulasso strains, respectively. This efficacy may be due to its major compounds which are with major compounds as ß-caryophyllene, p-cymene, thymol acetate and 1.8 cineol. Interestingly, on all strains, C8 combination showed a synergistic effect while C2 showed an additive effect. These combinations exhibit a rate of mortality varying from 80 to 100%. Their toxicity would be due to the major compounds and the putative combined effects of some major and minor compounds. More importly, L. multiflora EO and combinations of C. nardus and O. americanum EO, may be used as alternatives against pyrethroid resistants of Ae. aegypti.