Larvicidal and Synergistic Activities of Crude Leaf Extracts of Pyrethrum (Chrysanthemum), Eucalyptus camaldulensis Sm. (Myrtaceae) and Nicotiana tabaccum (Tobacco) against the Larvae of the Malaria Vector Anopheles gambiae s.s. Giles (Diptera: Culicidae)

The present study was undertaken to evaluate larvicidal efficacy of crude leaf extracts of Pyrethrum, Eucalyptus camaldulensis and Nicotiana tabaccum individually and in combination (synergistic activities) of the extracts against third instar larvae of Anopheles gambiae s. s. Giles. In the individual extract tests it was found that pyrethrum DCM extract exhibited best activity achieving 100 % mortality of third instar larvae at LC50 164.86 ppm and LC90 255.17 ppm. This was followed by the DCM extract of Eucalyptus camaldulensis (LC50 168.58 ppm, LC90315.85ppm). Nicotiana tabaccum was third LC50 (189.58 ppm, LC90 320.75 ppm). The results revealed that pyrethrum extract was more toxic plant when tested individually. In the synergistic tests a total of 30 combinations of extracts (comprising of 30 treatments) amongst the three plants were tested. It was observed that the maximum synergistic activities were found in the combination extracts of DCM and Methanol in the ratio 11 (v/v) (pyrethrum and Eucalyptus camaldulensis extracts respectively) at 118.65 ppm. Other combinations that exhibited good activities were DCM combination of ethyl acetate (pyrethrum and Eucalyptus camaldulensis extracts respectively), DCM combination of hexane (Pyrethrum and Nicotiana tabaccum extracts respectively) and DCM combination of hexane (Eucalyptus camaldulensis and Nicotiana tabaccum extracts respectively). These combinations exhibited appreciable activities by achieving 100 % larval mortality at 121.45, 127.85, 130.78 and 135.55 ppm respectively. The results of the study revealed that pyrethrum plant leaves individual and/or combinations with extracts of Eucalyptus camaldulensis and Nicotiana tabaccum can be used as a potent source of natural mosquito larvicidal agent to replace the synthetic insecticides.