Effect of Water Bodies Lining on the Efficacy of Molluscicides Against Biomphalaria alexandrina Snails with Emphasis to their Integrated Control Measures

The effect of lining snails'aquaria with different materials on efficacy of the molluscicides niclosamide and copper sulphate on Biomphalaria alexandrina snails under laboratory and semi-field conditions was studied. Under laboratory conditions, the survival rate of B. alexandrina kept in aquaria lined with cement or plastic sheets and exposed to the sub-lethal concentration(LC₅₀) of niclosamide showed a highly significant reduction (p<0.001) represented by 5% and 0.0, respectively comparing with those in mud and control₁ (50% and 40%, respectively). Similarly, snails kept in aquaria with substratum of cement or plastic and exposed to copper sulphate (LC₅₀) showed 100% mortality compared to those with muddy substratum and control₁ (65% and 50%, respectively). The Semi-field experiment showed 100% and 96% snails mortality in canals lined with cement or plastic, respectively after exposing to copper sulphate (LC₂₅) compared to 38% for snails in muddy canal. The mortality of control snails (snails without molluscicide) was recorded as 2%, 52% and 48% in canals with mud, cement and plastic, respectively. By using the sublethal concentration (LC₂₅) of the niclosamide, there was a highly significant increase in snails mortality in both of canals lined with cement and plastic (100%) compared to 40% in snails maintained in muddy canals (p<0.001). A highly significant reduction (p<0.001) was recorded in the survival rate of B. alexandrina kept with the competitor snails Helisoma duryi in both of the aquaria with mud and control₁ groups either in the case of free snails (40% and 53.3%, respectively) or those in cages (53.3% and 46.7%, respectively) compared to those of H. duryi (80% and73.3% for free snails and those in cages, respectively). The same pattern was observed in the semi-field experiment. Laboratory study on the role of lining on the integrated control of snails maintained in mud substratum with the competitor snails and molluscicide indicated that there was a highly significant reduction (p<0.001) in snails mortalityrepresented by 55% in case of both of the two molluscicides compared to those snails exposed in the presence of lining materials cement and plastic (92.5% and 100%., respectively). In addition, 100% mortality of B. alexandrina snails was observed after exposing to the molluscicide copper sulphate and H. duryi snails in both of the canals lined with cement and plastic compared to snails maintained in muddy canals (68%). From the view of snail integrated control measures, it could be concluded that lining of canals with cement or plastic sheets improve and increase the efficacy of the molluscicides and the bio-control agents (snail competitors) against snail borne parasitic diseases.