Insecticidal Activities of Chromolaena odorata and Vernonia amygdalina leaf extracts against Anopheles gambiae [Diptera: Culicidae]

Abstract

Female Anopheles mosquitoes are the vectors of human malaria. The use of chemical insecticides for vector control has hampered with environmental pollution and insect. This suggests the need for the development of more potent and environment-friendly insecticides for effective control of malaria.This research investigated the larvicidal, pupicidal and adulticidal activities of Chromolaena odorata and Vernonia amygdalina leaf extracts against, An. gambiae in the laboratory at ambient temperature of 28 ± 2 °C and 75 ± 5% relative humidity. Different concentrations of 20 mg/L, 40 mg/L, 80 mg/L, 120 mg/L and 160 mg/L were prepared and these aqueous solutions were used for the experiments. Larval, pupal and adult mortality of An. gambiae were tested after 24 hours of exposure. Results showed that there were significant differences (P < 0.05) in toxicity level of the two plant extracts on An. gambiae larvae, pupae and adults. Vernonia amygdalina extract was the most toxic to An. gambiae larvae at all tested concentrations of 20 mg/L, 40 mg/L, 80 mg/L, 120 mg/L and 160 mg/L causing 47.5%, 82.5%, 100%, 100% and 100% mortality after 24 hours of treatment, respectively. Chromolaena odorata extract caused 32.5%, 60%, 82.5%, 92.5% and 100% mortality of An. gambiae larvae after 24 hours of treatment at concentrations 20 mg/L, 40 mg/L, 80 mg/L, 120 mg/L and 160 mg/L, respectively. Vernonia amygdalina extract was the most lethal to An. gambiae pupae and adults which caused 55% mortality of adult An. gambiae at concentration 160 ml/L. The concentration of C. odorata and V. amygdalina leaves extracts required to evoke 50% death of An. gambiae adult were 296.20 mg/L and 147.98 mg/L respectively. The LC 90 of C. odorata extract was 3107.55 mg/L while V. amygdalina extract was 2221.05 mg/L for mosquito adults. The plant extracts were not as effective against adults compared to larva and pupa of An. gambiae. This study showed that C. odorata and V. amygdalina were toxic to malaria vector with V. amygdalina being more potent. This suggest that V. amygdalina extracts could serve as an alternative method to synthetic chemical control of malaria vectors.