Helisoma duryi as a biocontrol agent under laboratory conditions: I-competitive interactions between helisoma duryi and biomphalaria Alexandrina snails

ABSTRACT

Helisoma duryi has been suggested as a bio-control agent against the intermediate host of Schistosoma mansoni. In the present laboratory study, information was obtained concerning the interspecific competition between H. duryi and B. alexandrina snails. The obtained results revealed that the mortality rate among the adult B. alexandrina snails was significantly increased. Besides the hatching of the egg masses and further development of the juveniles were highly influenced by the presence of Helisoma. Some chemical changes in the water conditioned by Helisoma occurred in the form of significant reduction of calcium, chloride and pH. While there was a significant increase in potassium, sodium which led to significant reduction in Ca/Ma, Ca/Na and Ca/K ratios. The results also demonstrated that water conditioned by by H. duryi decreased the egg hatchability of B. alexandrina and impeded the development of newly hatched snails. This was highly manifested among egg masses in water conditioned for 60 days. The egg hatchability of the target snails in association with Helisoma was affected by the availability of the food supply. It was noticed that the number of hatched egg masses decreased as the number of Helisoma increased. H. duryi was a voracious feeder, it eats the leaves themselves. The behavior was more pronounced when the acquaria were devoid of food supply