DETERMINATION OF CHEMICAL COMPOSITION AND LARVICIDAL EFFICACY OF ESSENTIAL OILS OF Cymbopogon citratus, Chrysanthemum cinerariifolium AND Rosmarinus officinalis IN MERU AND THARAKA NITHI COUNTY AGAINST Aedes aegypti (DIPTERA: CULICIDAE)

Abstract

Aedes aegypti is the mosquito species responsible for the viruses that cause yellow fever, zika disease, chikungunya fever and dengue fever. The four diseases have no cure, necessitating mosquito control as the proven ways of minimizing human vector contact eventually lead to reduced infections and prevalence rates of these diseases. The existing methods employ the use of insecticides, which present a number of challenges, including resistance, toxic hazards to the environment, non-target organisms, and humans. This study aimed to determine the chemical composition and larvicidal potential of essential oils extracted from Cymbopogon citratus, Chrysanthemum cinerariifolium, and Rosmarinus officinalis against Aedes aegypti larvae. These plants are preferred because of their earlier applications, traditionally as insecticides and pesticides. Plant materials (twigs, flowers, and leaves) were collected from Meru and Tharaka Nithi Counties, Kenya, and subjected individually to hydro-distillation for essential oil extraction. The chemical constituents of the oils were analyzed using a Thermo-Scientific Trace 1310 GC-MS system, and retention indices were calculated from mass spectra. The analysis revealed that C. cinerariifolium contained the highest number of compounds, predominantly the sesquiterpenes; α muurolene (30.98%) and β-farnesene (27.73%). R. officinalis was rich in the monoterpene α-pinene (21.96%), and the monoterpenoid eucalyptol (20.04) while C. citratus was dominated by the monoterpenoids; geranial (28%) and neral (19.01%). Bioassays demonstrated significant larvicidal activity, with C. cinerariifolium exhibiting the highest potency (LC₅₀ = 0.003 mg/L at 24 h), achieving 100% larval mortality at concentrations as low as 0.1 % concentration. R. officinalis (LC₅₀ = 0.056 mg/L at 24 h) and C. citratus (LC₅₀ = 0.610 mg/L at 24 h) also displayed activity, The LC50 and LC90 of R. officinalis and C. Citratus have no significant difference in the first 24 hours while C. cinerariifolium shows a significant difference and much lower, indicating that C. cinerariifolium is most potent though less pronounced. Therefore, essential oils from the three plants can be applied at different concentrations to counteract A. aegypti larva. The findings of this study show that the presence of sesquiterpenes in the essential oils increases the potency of A. aegypti larva, highlighting the potential of these plants, especially C. cinerariifolium, as promising natural alternatives for mosquito vector management