Abstract:
Laboratory studies were conducted to determine the effects of Bacillus thuringiensis var. israelensis on 4 species of non-target aquatic organisms. Results showed that the young giant prawn (Macrobrachium rosenbergii de Man) was the most susceptible species to this bacteria, the small water bug (Diplonychus rusticum Fabr.) was more susceptible than the nile tilapia (Tilapia nilotica (Linn.)) and the guppy (Poecilia reticulata Peters) was the least susceptible species (p > 0.01). The 24-hr LC50values for the young giant prawn, the small water bug, the nile tilapia and the guppy were 352, 2259, 4217 and 5662 ppm, respectively; and the 96-hr LC50 values were 280, 1901, 4036 and 5346 ppm, respectively. The toxicity of this bacteria on these organisms was found to be highly effective during the first 48 hours. The thresholds of toxicity of thrin, - giensis var. israelensis to the young giant prawn, the small water bug, the nile tilapia and the guppy were 269, 1899, 4034 and 5344 ppm, respectively. The safe concentrations would be in the range of 6-14, 38-95, 81-202 and 107-267 ppm, respectively. The 6 month chronic toxicity studies in the guppy showed no differences in weight, the number of offsprings and length among control, bacterial concentration at 10 and 500 ppm (p < 0.05). There was no differences in water quality among these three treatments. These studies indicated that B. thuringiensis var. israelensis had no effect on these 4 species of non-target organisms particularly at the concentration of 10 ppm which will be recommended for use in mosquito control.