Molluscicidal activities of aqueous extract of the sea anemone Parasicyonis actinostoloides against vector snails Bulinus truncatus and Lymnaea natalensis.

The aqueous extract of the sea anemone Parasicyonis actinostoloides showed molluscicidal effect against vector snails of Schistosoma hacematobium and Fasciola gigantica after 24 hours of exposure. LC50) and LC90 values for P. actinostoloides were 40 & 78.6 ppm for B. runcatus and 46.6 & 86.5 ppm for L. natalensis respectively. The effect of continuously exposure of B. truncatits and L. naltlensis to sublethal aqueous extract concentrations (LC0, LC10 & LC25) on survival rate, egg production and on infectivity of miracidia to infection with S. haematobium and F. gigantica were studied. The data showed that no B. truncatus survived more than 42, 32 & 27 days after exposure with a mean life span of 18.5, 13.3 & 11.1 days respectively. The death rate of B. truncatus with LC0 was highly significant as compared to treatment with LC10 & LC25 (p < 0.01). L. natalensis were more susceptible to the effect of aqueous extract than B. truncatus. LC0, LC10 & LC25, extract killed all L. natalensis through 32, 27 & 22 days. The mean life span of those exposed to LC0 was 12.37 days, high significant when compared with treated LC10 & LC25 ones (p < 0.01). The cumulative mortality rates of B. truncatus and L. natalensis in controls during the experimental study (52 days) was 60% & 75%, respectively. Egg production of B. truncatius and L. natalensis was not affected by sublethal concentrations. Control snails layed significantly higher no. of eggs than treated ones. B. truncatus stopped egg laying 17 days after exposure to LC25. those treated with LC10 & LC0 ceased to deposit eggs after 22 & 27 days respectively. The percent reduction in egg laying capacity of B. truncatus treated with LC0, LC10 & LC25 compared to controls was 77.1%, 93.2% & 92.8% respectively (p < 0.01). Similar reduction in egg production of treated L. natalensis cornpared to controls occurred, the percent reduction in egg production of snails treated with LC0, LC10 & LC25 in relation to controls was 78.4%, 92.4% & 94.7% respectively. Sublethal concentrations of aqueous extract of P. actinostoloides affected hatchability of B. truncatus and L. natalensis eggs. The data showed that eggs of B. truncatus and L. natalensis can hatch in all tested concentrations but with different rates. The eggs' hatchability in snails exposed to LC0, LCIo & LC25 extract at 5 days old was 44%, 38% & 30% in B. truncatus respectively. In L. natalensis eggs, the corresponding rates were lower 28%, 24% & 18% respectively. The infection of B. truncatuts and L. natalensis with S. haematobium n and F. giganlica miracidia was greatly reduced by the sublethal concentrations of aqueous extract of P. actinostoloides. The reduction of infection rate increased with the increased of sublethal concentrations. In B. truncatus the reduction was 43.2%, 57.6% & 76.6% compared to controls and in L. natalensis was 56.3%, 70.2% & 77.4%, respectively.