Comparative insecticidal properties of Basotho medicinal plants against Culex quinquefasciatus (Diptera: Culicidae) mosquitoes from the Eastern Free State Province of South Africa

[摘要] Culex quinquefasciatus is a vector of human and animal disease causing pathogens that are ofsocioeconomic problem in developing countries. The mosquitoes have developed resistance againstsynthetic insecticides, hence the search for natural botanical insecticides. The present study wasaimed at investigating the secondary plant metabolites, cytotoxicity, larvicidal, pupicidal andinsecticidal potential of Artemisia absinthium, Artemisia afra, Cosmos bipinnatus, Foeniculumvulgare, Mentha longifolia and Tagetes minuta against C. quinquefasciatus. The leaf extractscontained mostly saponins, alkaloids, terpenoids, steroids and flavonoids. Plant aqueous and ethanolextracts exhibited cytotoxic effects for T. minuta (LC50 = 0.10 mg/ml; LC50 = 3.16 mg/ml), A.absinthium (LC50 = 2.89 mg/ml), C. bipinnatus (LC50 = 5.66 mg/ml; LC50 = 4.81 mg/ml), and A.afra (LC50 = 5.39 mg/ml) against brine shrimp nauplii. Ethanolic extract mortality andconcentration doses had was significant difference (F5,5 = 13.69; P < 001) towards naupliimortality. Most larvicidal bioactivities were observed in ethanolic and hexane extracts for F.vulgare (LC50 = 0.10 mg/ml; LC50 = 1.03 mg/ml), M. longifolia (LC50 = 1.05 mg/ml; LC50 = 0.10mg/ml), T. minuta (LC50 = 1.17 mg/ml; LC50 = 1.01 mg/ml) and A. afra (LC50 = 1.02 mg/ml; LC50= 1.14 mg/ml), and while larvae mortality and extract concentrations showed significant difference(F5,5 = 9.95; P < 0.01). Pupicidal bioactivity was displayed by both ethanolic and hexane extracts ofA. afra (LC50 = 1.10 mg/ml; LC50 = 1.04 mg/ml), T. minuta (LC50 = 1.11 mg/ml; LC50 = 1.12mg/ml), C. bipinnatus (LC50 = 1.14 mg/ml; LC50 = 1.16 mg/ml) and M. longifolia (LC50 = 1.13mg/ml; LC50 = 1.21 mg/ml). The extract concentration level were directly proportional to pupamortality percentage with M. longifolia (R2 = 0.85) and A. afra (R2 = 0.74). The aqueous extractshad no fatal effect on larvae and pupa at all the concentrations tested. The rate of knock-down washighest for M. longifolia (KD50 = 4.91 min-1) followed by F. vulgare (KD50 = 9.87 min-1), T. minuta(KD50 = 12.39 min-1), and A. afra (KD50 = 19.02 min-1). The insecticidal activity was greater in M.longifolia (LD99 = 0.25 g) followed by F. vulgare (LD99 = 0.25 g), T. minuta (LD99 = 0.25 g) and A. afra (LD99 = 0.25 g). The insecticidal mortality ratio between evaluated plants had significantdifference (F5,4 = 283.11; P < 0.01). In this study, ethanolic and aqueous extracts had morecytotoxic activity against A. salina nauplii than the hexane extracts, whereas, ethanolic and hexaneextracts exhibited stronger larvicidal and pupicidal activities than the aqueous extracts. The selectedBasotho medicinal plants possessed convincing insecticidal, pupicidal and larvicidal activities andtherefore can be recommended for mosquito control at Kroonstad as well as in nearby communitiesof the eastern Free State Province.

[发布机构] University of the Free State