Larvicidal Effect of Some Selected Salts Against the Dengue Vector Mosquito, Aedes aegypti (Diptera: Culicidae) in Bangladesh

Abstract Background The container breeding mosquito, Aedes aegypti is the major universal vector of dengue viruses capable of causing dengue fever (DF), dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). Vector control may have a potential role in reducing the morbidity and mortality of human by DHF/DSS. The purposes of this work were to evaluate the larvicidal effect of some salt solutions against the larvae of Ae. aegypti.Methods Freshly collected larvae were transferred to the laboratory and reared using rainwater as a rearing medium with yeast granules as larval food. Five salts i.e. AgNO3, HgCl2, CdCl2, CuSO4, and CuCl2 were tested to assess the larvicidal effect on both the 1st and 3rd instars larvae of Ae. aegypti. Serial concentrations (0, 1, 3, 5, 7 &10 ppm) of each salt were prepared by using distilled water as the solvent.Results Silver nitrate (AgNO3) was noted as the most effective larvicide followed by HgCl2, CdCl2, CuSO4 and CuCl2 against Ae. aegypti larvae. The LC50 of AgNO3 against 1st and 3rd instars larvae were 0.118 and 1.659 ppm, and the LC90 were 2 and 3.347 ppm, respectively. The LT50 of AgNO3(1 ppm) against 1st and 3rd instars larvae were 0.575 and 30.42hrs, and the LT90 was 6 and 67.49 hrs, respectively. All of the first instar larvae were killed and failed to pupate with every salt of each concentration (1–10 ppm) within 7 days. Whereas 3rd instar larvae were also unable to pupate entirely in AgNO3 and HgCl2 solutions but very few (5-36.66%) pupation was found at 7 ppm & higher concentrations of CdCl2, CuSo4, and CuCl2 salts. CdCl2, CuSo4 and CuCl2 prevented 66.66%, 57.14% and 50% adult emergences from pupae at 5 ppm concentration respectively. The order of decrease of toxicity for larval mortality was AgNO3 > HgCl2 > CdCl2 > CuSO4 > CuCl2 and for prevention of pupation & adult emergence was AgNO3 ≥ HgCl2 > CdCl2 > CuSO4 > CuCl2.Conclusions AgNO3 was found as a very good potential in the killing of Aedes aegypti larvae, prevention of pupae formation and adult emergence. Therefore, the results obtained could be considered a contribution to the search for eco-friendly larvicides of natural origin. Further studies are needed to understand the residual aquatic toxicity of this salt in the field.