RESUMO
The molluscicidal effect of Pittosporum tobira, Abutilon pictum and Thevetia peruviana leaves and seeds powder and ethanol extract against adult Biomphalaria alexandrina snails after 24 hrs of exposure under laboratory conditions showed that T peruviana is the most toxic ones since its LC[90] values were the least among the other tested plants, being 98.8 and 18.5 ppm for the dry powder water suspension and ethanol extract, respectively. Bioinphalaria snails continuously exposed to sublethal concentration [LC[0]=1.2ppm] of the ethanolic extract of T. peruviana exhibited a great reduction in survival rate, being 24% and 2% after 4 and 8 weeks post exposure compared to 76% and 56% for control group, respectively. The egg production of treated snails was significantly reduced from the first week of exposure. Thus, the mean number of eggs/snail/week at the 41h week was 42.2 and 223.3 eggs/snail for treated and control snails, respectively. The exposure of B. alexandrina to sublethal concentration of the ethanolic extract of T. peruviana for 4 weeks led to disturbance in some biochemical parameters. The protein content in the hemolymph and glycogen content in tissues of treated snails were significantly reduced compared to control groups. The ratios of reduction of protein content were 46.7% and 65% respectively. Meanwhile, the alkaline phosphatase activity and the glucose content were increased in the hemolymph of treated snails, than of control ones. The elevation ratios were 72.7% and 88.2%, respectively. The LC[0] of T. peruviana ethanol extract killed 65% of miracidia and 55% of cercariae after one hour of exposure and they were killed after 4 hrs and 5 his after exposure respectively