Biological control of Biomphalaria glabrata and B. straminea by the competitor snail Thiara tuberculata in a transmission site of schistosomiasis in Martinique, French West Indies.

In Martinique, intestinal schistosomiasis was discovered at the beginning of this century. The intermediate host snail, Biomphalaria glabrata, was considered in the past as a common species in the different habitats of the island, but during the last decade it has been found only in water-cress beds. Several of these water-cress cultures contained mixed populations of B. glabrata and B. straminea. Moreover, these habitats also constituted transmission sites for Schistosoma mansoni infection. In 1979 the thiarid snail Thiara ( = Melanoides) tuberculata was discovered in Madame river, Fort-de-France, and in the following years at other sites. In 1983 a programme of biological control using this snail was started in two groups of water-cress beds. In 1981-1982 the study site, Roxelane valley, sheltered important populations of B. glabrata (45-256 individuals/m2) and of B. straminea (2-30 ind./m2). In January 1983 the competitor T. tuberculata was introduced into the two groups of water-cress beds (1.3 and 1.7 ind./m2 respectively) and during subsequent years snail population sampling was carried out. The results showed rapid colonization by the competitor snail, whose densities reached 178 and 325 ind./m2 in November 1983 and a maximum of 9941 and 13,388 ind./m2 in October 1984. During that time, B. glabrata populations declined: 153 and 41 ind./m2 in November 1983, 4 and 0 ind./m2 in October 1984, and 0 ind./m2 in the two groups of water-cress beds in October 1985. A similar phenomenon was observed for B. straminea. Since October 1985 neither planorbid species has been found by exhaustive sampling of the habitats.(ABSTRACT TRUNCATED AT 250 WORDS)