Larvicidal Efficacy of Crude Essential Oil (Leaf Extracts) of Pyrethrum (Chrysanthemum: Compositae), Eucalyptus camaldulensis Sm (Myrtaceae) and Nicotiana tabaccum (Tobacco L.) (Solanaceace) against Third Instar Larvae of the Malaria Vector Anopheles gamb

In this study crude leaf extract of Pyrethrum, Eucalyptus camaldulensis and Nicotiana tabaccum (Tobacco) were tested for their larvicidal activity against Anopheles gambiae s. s. Giles (Diptera Cidicidae), a member of Anopheles gambiae complex. Six different solvents were used namely ethanol, methanol, dichloromethane (DCM), hexane, ethyl acetate and water (aqueous) for the preparation of crude extracts from the plant leaves. The larval mortality of the late third instar larvae of Anopheles gambiae s. s Giles after 24 hour of exposure were observed separately in control at 50, 100, 150, 200, 250, 300, 350 and 400 ppm concentrations of the leaf extract. The six different solvent extract 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 third instar larvae. In a similar response the DCM extract of Eucalyptus camadulensis recorded second highest activity at LC50 168.65 ppm and LC90 315.85 ppm causing a mortality of 100 %. Ethanol extract of pyrethrum exhibited high larvicidal activity at 167.78 ppm against third instar larvae of An. Gambiae s. s. than same extracts of Nicotiana tabaccum (189.58 ppm) and Eucalyptus camaldulensis (210.15 ppm). The rest of the extracts i. e. methanol, hexane, ethyl acetate and aqueous exhibited a range of varying activities from 197.46 ppm (methanol) to 260.56 ppm (ethyl acetate). There was no mortality observed in controls. A general observation made was that the third instar larvae were susceptible to all treatments. The larvicidal activity of the treatments were dose and time independent and all of the volatile oils showed significant larvicidal activity against Anopheles gambiae s. s. Giles larvae after 24 hours exposure. The LC50 and LC90 with their 95 percent confidence limits of the oils were determined using log probit analysis test (Finney, 1971) (1). From these results it was observed that the leaf extract of pyrethrum contain toxic compounds to mosquito larvae and therefore suggest that pyrethrum extract has potential in the control of the malaria mosquito and can be developed and used. Further studies of these plants as possible agents for mosquito control are recommended.