The efficacy of magnesium thermophosphate (a soil corrective and fertilizer) was tested as food for laboratory planorbids for a period of five weeks, during which time the shell growth of Biomphalaria glabrata (Say, 1818) and Helisoma duryi (Wetherby, 1879) experimental populations was observed. Surprisingly, this mineral product blocked the oviposition of both species from the second week on, when added to the latosoil either isolatedly or associatedly. Consequently, magnesium phosphate, when widely used in new agricultural areas obtained through modern irrigation methods, may be carried to lentic and lotic ecosystems by rain and reduce the pioneer populations of different Biomphalaria species, thus constituting a useful means of Schistosomiasis mansoni control in rural areas. Moreover, it may also be effective in the control of the Schistosoma mansoni intermediate hosts that usually live in fish-breading ponds whose increase in number is often encouraged as an alternative economic activity for the small rural owner or as a means for meeting nutritional requirements. This material may also control limnaeid populations, which are Fasciola hepatica intermediate hosts. Specific field tests that may actually demonstrate these hypotheses, as well as studies aiming to find out how the magnesium element blocks the mollusks' fertility, are suggested. The need for further research on the action on the eggs and young forms of planorbides and on miracidia cercariae (free and intra-snail) of trematodes, of different magnesium concentrations is pointed out.
Schistosoma mansoni; Planorbidae
