Larvicidal effect of selected salts against the dengue vector mosquito Aedes aegypti (Diptera: Culicidae) in Bangladesh

The container breeding mosquito Aedes aegypti (Linnaeus) is the major universal vector of dengue viruses that cause dengue fever (DF), dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). Vector control has an important role in reducing human cases of DHF/DSS. The purpose of this work was to evaluate the larvicidal effect of salt solutions against the larvae of Ae. aegypti. Freshly collected larvae were transferred to the laboratory and reared using rainwater as the rearing medium, with yeast granules as larval food. Five salts, AgNO3, HgCl2, CdCl2, CuSO4, and CuCl2, were tested to assess the larvicidal effect on both the 1st and 3rd instar larvae of Ae. aegypti. Serial concentrations (0, 1, 3, 5, 7 and 10 ppm) of each salt were prepared using distilled water as the solvent. Silver nitrate (AgNO3) was noted as the most effective larvicide, followed by HgCl2, CdCl2, CuSO4, and CuCl2. The LC50 values of AgNO3 against 1st and 3rd instar larvae were 0.118 and 1.659 ppm, and the LC90 values were 2 and 3.347 ppm, respectively. The LT50 values of AgNO3 (1 ppm) against 1st and 3rd instar larvae were 0.575 and 30.42 h, and the LT90 values were 6.00 and 67.49 h, respectively. All 1st instar larvae died, failing to pupate in every salt concentration (1-10 ppm) within 7 days. Third instar larvae were also unable to pupate entirely in AgNO3 and HgCl2 solutions but a very few (5.00-36.66%) pupations were found at 7 ppm, with higher concentrations of CdCl2, CuSo4 and CuCl2 salts. In addition, CdCl2, CuSo4 and CuCl2 prevented 66.66%, 57.14% and 50% of 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 in preventing pupation and adult emergence it was AgNO3≥HgCl2>CdCl2>CuSO4>CuCl2. AgNO3 was found to have 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.