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

ABSTRACT

The aqueous extract of the sea anemone Parasicyonis actinostoloides showed molluscicidal effect against vector snails of Schistosoma haematobium and Fasciola gigantica after 24 hours of exposure. LC 50 and LC 90 values for P. actinostoloides were 40 and 78.6 ppm for B. truncatus and 46.6 and 86.5 ppm for L. natalensis respectively. The effect of continuously exposure of B. truncatus and L. natalensis to sublethal aqueous extract concentrations [LC 0, LC 10 and LC 25] 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 and 27 days after exposure with a mean life span of 18.5, 13.3 and 11.1 days respectively. The death rate of B. truncatus with LC 0 was highly significant as compared to treatment with LC 10 and LC 25 [p<0.01]. L. natalensis were more susceptible to the effect of aqueous extract than B. truncatus. LC 0, LC 10 and LC 25 extract killed all L. natalensis through 32, 27 and 22 days. The mean life span of those exposed to LC 0 was 12.37 days, high significant when compared with treated LC 10 and LC 25 ones [p<0.01]. The cumulative mortality rates of B. truncatus and L. natalensis in controls during the experimental study [52 days] was 60% and 75%, respectively. Egg production of B. truncatus 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 LC 25. those treated with LC 10 and LC 0 ceased to deposit eggs after 22 and 27 days respectively. The percent reduction in egg laying capacity of B. truncatus treated with LC 0, LC 10 and LC 25 compared to controls was 77.1%, 93.2% and 92.8% respectively [p<0.01]. Similar reduction in egg production of treated L. natalensis compared to controls occurred, the percent reduction in egg production of snails treated with LC 0, LC 10 and LC 25 in relation to controls was 78.4%, 92.4% and 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 LC 0, LC 10 and LC 25 extract at 5 days old was 44%, 38% and 30% in B. truncatus respectively. In L. natalensis eggs, the corresponding rates were lower 28%, 24% and 18% respectively. The infection of B. truncatus and L. natalensis with S. haematobium and F. gigantica 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% and 76.6% compared to controls and in L. natalensis was 56.3%, 70.2% and 77.4%, respectively