A review of helisoma duryi in biological control.

Biological control of schistosomiasis by means of introduction of the north American planorbid snail, Helisoma duryi, as a competitor of the intermediate host snails has been proposed. The systematics of the genus Helisoma and the geographic distribution of the different species is described. Papers dealing with laboratory experiments or field observations on the competition between H. duryi and different intermediate host snails have been reviewed. The status of H. duryi as intermediate host of trematodes has been evaluated by searching the literature for all the trematode species that are recorded from the genus Helisoma. The list does not include trematodes of medical or veterinary importance and despite many attempts it has not been possible to infect H. duryi with Schistosoma mansoni and S. haematobium. Finally this paper makes a few comments on the experiments that should be performed in the laboratory, under semifield conditions and and field conditions before H. duryi should be actively dispersed in Africa. The aspects to be considered include the nature of the competitive interactions, the relation between H. duryi and different medical and veterinary important trematodes and the effect of H. duryi on the biotope.