Evaluation of the Larvicidal Activity of the Fractions of Hyptis suaveolens on 4th instar larvae of Culex quinquefasciatus

Abstract Mosquitoes are important vectors that transmit many communicable diseases throughout the world. Billions of people face major health concern throughout the world due to vector borne diseases. Synthetic insecticides such as organophosphate and pyrethroids are commonly used for their control. However, insecticidal compounds from natural sources, such as plants are promising tools for managing vectors. The present study was conducted to evaluate the efficacy of Hyptis suaveolens on Culex quinquefasciatus. Extraction of the plant using hexane and ethyl acetate yielded hexane (coded A) and ethylacetate (coded B) leaf extracts. Extract B which attained 100% mortality at 24 hours of exposing the larvae of C. quinquefasciatus (in a previous study) was further fractionated to obtain 5 fractions coded B1-B5. Crude ethylacetate leaf extract of H. suaveolens and its fractions were evaluated for their potentials in vector control of mosquito-borne diseases using World Health Organization’s recommended protocols for testing the efficacy of insecticides. Crude extract at 0.066g/ml attained 100% mortality and complete inhibition of pupation as well as inhibition of adult emergence of the larvae after 72 hours while that of the fractions B1-B5 was at 0.055g/ml and 0.066g/ml after 24 hours of larval exposure to the extract respectively. Fraction B1 was most potent. The mean LC50 and LC90 were 0.046 and 0.461, 0.250 and 0.501, 0.040 and 0.478, 0.185 and 0.730, 0.038 and 0.374, 0.080 and 0.401 of crude extract and its fractions respectively. The values of R2 (coefficient of determination) obtained indicated the rate of mortality linearly increased with increasing dose. The phytochemical constituents detected were alkaloids, anthraquinones, balsams, carbohydrates, glycosides, saponins, terpenes, volatile oils and flavonoids. The present study revealed the potential of fractions of H. suaveolens in controlling vector borne diseases (Avian malaria, West nile virus, St. Louis and Japanese encephalitis).