Chemical Composition and Use of <i>Momordica charantia</i> L. and <i>Hyptis spicigera</i> Lam. Extracts as Mosquito Larvicides and Insect Growth Regulators against Malarial Vector, <i>Anopheles gambiae</i> Giles

Abstract

Background: Mosquitoes are responsible of numerous vector-borne diseases and among these diseases is malaria which takes away lives of thousands of people, especially children of under five, particularly in Africa. To reduce the mortality and economic burdens of this deadly disease, synthetic insecticide has been of use to control its main vector, Anopheles gambiae. Due to adverse effects caused by these conventional products on non-target organisms and the environment, plants have been of first choice as they proved their effectiveness against mosquitoes and are said to be eco-friendly and relatively safer. Therefore, the aim of this study was to screen the phytochemicals and determine the larvicidal and adult emergence exhibitory activities of Momordica charantia and Hyptis spicigera leaves extracts against Anopheles gambiae larvae. Methods: The WHO standard protocol for larvicidal activity and IGRs was followed up and concentrations from 500 - 2000 ppm for larvicidal and 500 - 1500 ppm for IGRs were set up. Results: There was the presence of alkaloids, flavonoids, tannins, phenols, steroids, terpenoids and oils in Momordica charantia against alkaloids, taponins, tannins, phenols, steroids, terpenoids and oils in Hyptis spicigera. Methanol crude extract registered the lowest LC50 value of 270.6 ppm followed by ethyl acetate and hexane fractions recorded the LC50 of 742.1 and 756 ppm, respectively for larvicidal activity of Momordica charantia against LC50 of 760 and 867.5 ppm for hexane fraction and methanol crude extract, respectively for Hyptis spicigera. Methanol crude extract and hexane fraction of both plants as well as the ethyl acetate fraction of M. charantia registered greater emergence inhibition with IE50 values of 590.2, 842.3 and 982 ppm for methanol crude extract, hexane and ethyl acetate fractions of M. charantia, respectively against 901.7 and 873.2 for methanol crude extract and hexane fraction of H. spicigera, respectively. Conclusion: The toxicity and adult emergence inhibition may be associated with constituents in both plants that interfere with the normal neuronal, respiratory and endocrine systems functions.