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Title: Toxicity of six plant extracts and two pyridine alkaloids from Ricinus communis against the malaria vector Anopheles gambiae

Author
item WACHIRA, SABINA - International Centre Of Insect Physiology And Ecology
item OMAR, SABAR - Kenya Medical Research Institute
item JACOB, JULIA - International Centre Of Insect Physiology And Ecology
item WAHOME, MARTIN - Institute Of Tropical Medicine
item Alborn, Hans
item SPRING, DAVID - University Of Cambridge
item MASIGA, DANIEL - International Centre Of Insect Physiology And Ecology
item TORTO, BALDWYN - International Centre Of Insect Physiology And Ecology

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2014
Publication Date: 7/4/2014
Citation: Wachira, S.W., Omar, S., Jacob, J.W., Wahome, M., Alborn, H.T., Spring, D.R., Masiga, D.K., Torto, B. 2014. Toxicity of six plant extracts and two pyridine alkaloids from Ricinus communis against the malaria vector Anopheles gambiae. Parasites & Vectors. 7:312-319.

Interpretive Summary: The principal vector of P. falciparum in sub-Saharan Africa is An Anopheles gambiae Giles s.s. Knowledge of the vector’s interaction with plants can lead to the development of new malaria control tools. After emergence, both males and females almost exclusively feed on plant-derived sugary fluids including sap, nectar, and honeydew in order to supplement their energy reserves and to sustain life. Scientists at USDA, ARS, Center for Medical, Agricultural and Veterinary Entomology, Gainesville, FL, International Centre of Insect Physiology and Ecology, Nairobi, Kenya, Kenya Medical Research Institute, Jomo Kenyatta University of Agriculture and Technology, Nairobi, Kenya and University of Cambridge, Cambridge, UK investigated the toxicity and larvicidal activity on this vector of extracts from six selected plants found in Kenya and identified two compounds from Ricinus communis: 3-carbonitrile-4-methoxy-N-methyl-2-pyridone (ricinine), and its carboxylic acid derivative 3-carboxy-4-methoxy-N-methyl-2-pyridone. It was discovered that extracts from the six plant species exhibit varying bioactivity against the larvae and adult females. T. diversifolia and R. communis showed highest bioactivity against adult females An. gambiae and larvae while longevity of female An. gambiae s.s. decreased with exposure time to the two pure compounds. This exploratory research demonstrated the potential for utilizing native plants for the control of this principal vector of malaria in sub-Saharan Africa.

Technical Abstract: The African malaria vector, Anopheles gambiae s.s., is known to feed selectively on certain plants for sugar sources. However, the adaptive significance of this behavior especially on how the extracts of such plants impact on the fitness of this vector has not been explored. This study determined the toxicity and larvicidal activity on this vector of extracts from six selected plants found in Kenya and two compounds identified from Ricinus communis: 3-carbonitrile-4-methoxy-N-methyl-2-pyridone (ricinine), and its carboxylic acid derivative 3-carboxy-4-methoxy-N-methyl-2-pyridone, the latter compound being reported for the first time from this plant. Of the six plants screened, extracts from T. diversifolia and R. communis were the most toxic against adult female mosquitoes after 7 days of feeding, with LC50 of 1.52 and 2.56 mg/mL respectively. Larvicidal activity of all the extracts increased with the exposure time with the highest mortality recorded for the extract from R. communis after 72 h of exposure (LC50 0.18 mg/mL). Mosquitoes fed on solutions of the pure compounds, 3-carboxy-4-methoxy-N-methyl-2-pyridone and ricinine survived almost as long as those fed on the R. communis extract with mean survival of 4.93 ± 0.07, 4.85 ± 0.07 and 4.50 ± 0.05 days respectively. Overall, these findings demonstrate that extracts from the six plant species exhibit varying bioactivity against the larvae and adult females of An. gambiae s.s. T. diversifolia and R. communis showed highest bioactivity against adult females An. gambiae and larvae while longevity of female An. gambiae s.s. decreased with exposure time to the two pure compounds.