Effect of extracts from selected Aloe plant species on the Anopheles gambiae, Sensu stricto and Aedes aegypti mosquitoes

Abstract

Malaria control through insecticide application has significantly been compromised by the advent of resistance to the insecticide in the Anopheles mosquito vector. These developments have necessitated the need to bio prospect for and understand the mode of action of novel insecticide introduction. Larvicidal potential in extracts from Aloe plants on Anopheles gambiae sensu stricto and Aedes aegypti third instar (two days old) larvae were evaluated. Extracts were obtained from Aloe turkanensis, Aloe ngongensis and Aloe fibrosa plants using classical solvent extraction technique. Larvicidal potential of the extract were evaluated through bioassay of the extract on third instar An. gambiae s.s and Ae. aegypti larvae following 24 h exposure. The dose-response data obtained were analyzed by probit analysis to establish the median lethal concentration (LC50) of the extract to the larvae. The LC50 responses against third instar larvae of An. gambiae s. s. and Ae. aegypti were 0.08 mg / ml and 0.11mg / ml, respectively at 95% intervals. All the A. ngongensis plant extracts had larvicidal activity. Only the methanol, acetone and hexane plant extracts of A. fibrosa species showed larvicidal activities at LC50 concentrations ranging between 0.66 and 3.90 mg / ml at 95% confidence interval. Phytochemical tests showed presence of flavonoids, tannins and saponins in Aloe turkanensis plant extract. Apart from the hexane and chloroform plant extracts of Aloe ngongensis, those of methanol, acetone and ethyl acetate showed presence of flavonoids. All the Aloe fibrosa plant extracts of hexane, acetone and methanol showed presence of flavonoids and tannins. However, only the acetone and methanol plant extracts of Aloe fibrosa showed presence of saponins. None of the Aloe plant extracts gave positive test for phlobatannins, terpenoids and steroids. The phenolic functional group was prevalent in most of the plant extracts. The leased significant difference (LSD) of the means of the developmental stages of the Aloe exposed Ae. aegypti were significantly different from those of the negative controls at 5% level. The leased significant means of the egg deposits, egg viability and mortality were significantly different in the Aloe exposed Ae. aegypti at 5% level The findings of this study will contribute to current Anopheles vector control programs by providing information on potential additional anti-Anopheles compound(s) and molecular process (es) of subtractive hybridization with bioinformatics, that can be exploited in development of novel insecticides.