Larvicidal, pupicidal and insecticidal activities of <i>Cosmos bipinnatus</i>, <i>Foeniculum vulgare</i> and <i>Tagetes minuta</i> against <i>Culex quinquefasciatus</i> mosquitoes

Abstract

Purpose: To evaluate the larvicidal, pupicidal and insecticidal activities of Cosmos bipinnatus , Foenuculum vulgare and Tagetes minuta leaf extracts against Culex quinquefasciatus mosquitoes. Methods: The leaves of the plants were extracted with distilled water, ethanol (95 %), and hexane and the extracts screened for their phytochemical profile. While larvicidal and pupicidal activities were assayed at concentrations ranging from 0.1 - 10 mg/mL, insecticidal property was tested at varying amounts (0.25 - 2 g) of the plant sample. The respective larval mortality was thereafter evaluated using Probit analysis. Results: Saponins, terpenoids, flavonoids and steroids were detected in the plant extracts. The ethanol extracts of F. vulgare , T. minuta and C. bipinnatus exhibited larvicidal activity half-maximal lethal concentration (LC 50 ) of 0.10, 1.17 and 1.18 mg/mL, followed by hexane extracts with LC 50 value of 1.03, 1.01 and 1.27 mg/mL, respectively, against the larvae of C. quinquefasciatus mosquito. Hexane extracts displayed pupicidal activity with LC 50 of 1.07, 1.12 and 1.16 mg/mL against F. vulgare , T. minuta and C. bipinnatus , respectively, while the ethanol extracts of T. minuta , C. bipinnatus and F. vulgare displayed pupicidal activity at LC 50 of 1.11, 1.14 and 1.31 mg/mL respectively, against pupa of C. quinquefasciatus mosquito. The aqueous extracts had no ( p > 0.05) lethal effects on both larvae and pupa of C. quinquefasciatus at all evaluated concentrations. F. vulgare had the highest (p 0.05) knock-down or lethal effects on the adult mosquito. Conclusion: C. bipinnatus , F. vulgare and T. minuta possess larvicidal and pupicidal properties against C. quinquefasciatus , whereas only F. vulgare and T. minuta displayed insecticidal properties. Consequent upon these findings, all the plants can be considered naturally potent larvicidal and pupicidal agents against C. quinquefasciatus. Keywords: Cosmos bipinnatus , Culex quinquefasciatus , Botanical insecticides, Knock-down effect, Larvicidal, Pupicidal, Insecticidal, Foeniculum vulgare , Tagetes minuta