Biological control and invading freshwater snails. A case study

Introductions of four species of freshwater snails occurred between 1972 an d 1996 onto Guadeloupe Island. Two of them, Melanoides tuberculata and Mari sa cornuarietis, were subsequently used as biological control agents agains t Biomphalaria glabrata, the snail intermediate host of intestinal schistos omiasis. In 1996, a general survey was carried out in 134 sites which had a lready been investigated in 1972. The total number of mollusc species had i ncreased from 19 to 21. Site numbers housing B. glabrata and two other spec ies had strongly declined. This decline may be mainly attributed to a compe titive displacement by M. tuberculata and M. cornuarietis as illustrated by several biological control programmes. There were no changes in the remain der of the malacological fauna. (C) 1999 Academie des sciences/Editions sci entifiques et medicales Elsevier SAS.