Experimental colonization of new habitats by Galba truncatula O.F. Müller (Gastropoda: Lymnaeidae) in central France and their susceptibility to experimental infection with the trematode Fasciola hepatica L

Abstract

Experimental introductions of Galba truncatula in new habitats were carried out over the 30 last years in the department of Haute-Vienne (central France) to study the details of snail settlement and the outcome of these populations, and to determine if the susceptibility of these new colonies to experimental infection with Fasciola hepatica did not change over time. A total of 51 samples (100 adult snails each) were collected from three populations known for their high susceptibility to F. hepatica infections (> 60 %). Each sample was introduced in March in an open drainage furrow (36 meadows) or a road ditch (15 sites) which had never been inhabited by snails. Introduced snails from 22 samples survived in 9 furrows and 13 road ditches. In these sites, the number of overwintering G. truncatula increased up to the second or third year post-introduction and progressively decreased in the following years to become stable from the sixth or seventh year (less than 40 snails per site). In 13 populations (out of 22), experimental infections of snails with F. hepatica did not result in significant variations in survival rates or in prevalences of infections when compared to the respective rates recorded in the three original populations. Conversely, in the nine other populations, experimental infections of snails resulted in a decrease in prevalence (< 40 %), whereas the survival rates of snails at day 30 post-exposure did not change. This last result might be explained by a change in natural parasite pressure in the new habitats, being probably lower than that existing in the three sites inhabited by the populations of origin.