Toxic and growth retarding effects of three plant extracts on Culex pipiens larvae (Diptera: Culicidae).

Abstract

The toxic and/or development retarding effects on Culex pipiens mosquito larvae by methanol and ether extracts of Azadirachta indica, Rhazya stricta and Syzygium aromaticum were investigated separately. All were found to show biological activity, however, the methanol extracts showed the most profound effects. R. stricta showed marked acute (2 d) and chronic (10 d) toxic effects, having an LC(50) and 95% CL of 251(209-326) and 140(110-178); 467(416-699) and 211(198-421) ppm, for the methanol and ether extracts, respectively. Only 3.3% of the larvae pupated and no adults emerged even at the lowest concentration (200 ppm) of methanol extract. Both A. indica extracts were toxic to C. pipiens larvae but at higher concentrations, showing an acute and chronic LC(50) and 95% CL of 824(692-980) and 265(111-481); 1620(1380-1892) and 675(514-887) ppm for the methanol and ether extracts, respectively. The methanol extracts of A. indica, at concentrations above 800 ppm, reduced pupation to 3.3% and completely inhibited adult emergence. Both extracts of S. aromaticum were less toxic to the larvae, however their influence on development was remarkable, causing complete inhibition of adult emergence at 200 and 600 ppm concentrations of the methanol and ether extracts, respectively. Future application of these extracts to larval habitats may lead to promising results in mosquito management programmes.