Background & objective: Vector control, using agents of chemical origin, continues to be practiced in the control of vector borne diseases. However, due to some drawbacks including lack of selectivity, environmental contamination, and emergence and spread of vector resistance, development of natural products for vector control has been a priority in this area. In the present study we evaluated the larvicidal and emergence inhibitory activities of a neem based formulation Neem Azal T/S 1.2 per cent EC against the vectors of malaria, filariasis and dengue.
Methods: Larvicidal and emergence inhibition (EI) activity of a neem formulation, NeemAzal T/S 1.2 per cent EC, was studied in the laboratory respectively against early 4(th) and early 3(rd) instar larvae of Anopheles stephensi, Culex quinquefasciatus and Aedes aegypti following standard procedures.
Results: Among the three vector species studied, An. stephensi was highly susceptible to NeemAzal T/S as revealed by the LC(50) and LC(90) values (1.92 and 2.76 ppm). The formulation produced an overall mortality or inhibition of emergence of 90 per cent (EI(90), when 3(rd) instar larvae were treated) at 0.046, 0.208 and 0.866 ppm in An. stephensi, Cx. quinquefasciatus and Ae. aegypti, respectively. The corresponding EI(50) values were 0.006, 0.048 and 0.249 ppm. On treatment, NeemAzal T/S induced certain morphogenetic abnormalities, broadly characterized in five types, in larvae, pupae and adults of all the three vector species. The percentage of dead specimens of any stage showing morphogenetic abnormalities was the maximum in Cx. quinquefasciatus (14.4%; n=2113) followed by Ae. aegypti.
Interpretation & conclusion: Our results indicated that because of its emergence inhibition activity, NeemAzal T/S 1.2 per cent EC could be a promising candidate for the use in integrated vector management programme and replace chemical insecticides.