A Comparison Of The Toxicity Of Calcium And Sodium Hypochlorite Against Culex Pipiens (Diptera: Culicidae) Larvae

The larvicidal activities of sodium and calcium hypochlorite against the filaria vector Culex Pipiens were investigated under laboratory conditions. The different larval instars were exposed to different concentrations of sodium and calcium hypochlorite and the lethal concentrations were estimated. Calcium hypochlorite was more toxic to all larval instars than sodium hypochlorite. The estimated LC 50 values of sodium hypochlorite for 1st, 2nd, 3rd and 4 th instar larvae, were 12.24, 46.2, 65.33 and 99.5 ppm, respectively. Meanwhile, the LC 50 values of calcium hypochlorite were 1.3, 5.75, 8.7 and 10.6 ppm for 1 st , 2 nd , 3 rd and 4 th larval instars, respectively. Both compounds caused mortality in all larval instars. Calcium hypo- chlorite was more effective than sodium hypochlorite when mosquito larvae were exposed from the start of the 1 st instar onwards. Hypochlorite compounds significantly reduced larval survival rates and induced significant prolongation in the duration of larval instars and development period. Larvae treated with sublethal concentrations of hypochlorite compounds suffered from severe inhibition of integu- ment development which was very fragile and ruptured easily. Most of treated larvae failed in splitting their exuviae and were unable to liberate themselves from the larval cuticle. Thesiphon of most treat- ed larvae was wider and paddle filled with black patches.