Larvicidal and Antagonistic Activities of Crude Leaf Extracts of Pyrethrum (Chrisanthemam: Compositae), Eucalyptus camaldulensis Sm. Myrtaceae, and Nicotiana tabaccum (Tobacco L.) (Solanaceae) Against Third Instar Larvae of the Malaria Vector, Anopheles g

Crude leaf extracts of Pyrethrum, Eucalyptus camaldulensis and Nicotiana tabaccum (Tobacco) were individually and in combination tested for their larvicidal and antagonistic activities against third instar larvae of Anopheles gambiae s. s. Giles. The combination tests were targeted on antagonistic activities of the crude leaf extracts. Six different solvents were used namely Ethanol, Methanol, Dicholoromethane (DCM), Hexane, Ethyl Acetate and Aqueous for the preparation of crude leaf extracts from the plant leaves. The larval mortality of the third instar larvae of An. gambiae s. s. Giles was observed after 24 hours of exposure separately in control using 50, 100, 150, 200, 250, 300, 350 and 400 ppm. of crude leaf concentrations. For the individual crude leaf extracts all the six solvent extracts of the plants showed good larvicidal activity. The highest potency was recorded by DCM extract of pyrethrum (LC50 164.68 ppm, LC90 255.17 ppm) achieving 100 % mortality of the larvae. Ethanol extract of pyrethrum also exhibited appreciable larvicidal activity at 167.78 ppm depicting 89.70 % larval mortality than same extracts of Nicotiana tabaccum (189.58 ppm) and E. camaldunsisis (210.15 ppm) causing 75.0 % and 78. .5 % mortality respectively. The rest of the extracts i. e methanol, hexane, ethyl, acetate and aqueous exhibited a range of remarkable and varying activities i. e pyrethrum methanol 224.45ppm, E. camaldulensis hexane 198.56 ppm, N. tabaccum ethyl acetate 201.52 ppm and pyrethrum aqueous 247.84 ppm exhibiting mortality of 79.41 %, 73.65 %, 85.08 % and 77.24 % respectively. In combination activities for antagonism on a combination ratio of 11 (v. v) for all solvents used in crude leave extracts (30 treatments) it was observed that 12 combinations exhibited antagonistic activities (SFless than1), 15 indicated synergistic activities while 3 combinations were neither antagonistic nor synergistic.