A total of 850 pre-adult Galba truncatula (shell height, 4 mm), originating from four French snail populations differing in shell height at the adult stage (from 6.5 to 12 mm), were individually subjected at 20°C to single-miracidium infections with Fascioloides magna. At day 75 post-exposure, the surviving snails were dissected, and rediae and cercariae were counted. Snail groups differed in shell growth during the experiment: from 1.8 ± 0.4 mm in group A up to 4.0 ± 1.1 mm in group D. The prevalence of F. magna infection, the numbers of free rediae and cercariae significantly increased together with increasing growth of infected snails during the experiment. Group A produced 1-6 first-generation rediae per snail and the mean daughter redia production ranged from 7.5 second-generation rediae (when a single first generation per snail developed) to 2.3 (6 first-generation rediae per snail). In contrast, up to ten first-generation rediae were noted in group D, and each mother redia gave daughter rediae with averages ranging from 1.5 (ten first-generation rediae per snail) to 13 (a single first generation per snail). In conclusion, the development of F. magna in G. truncatula exhibited both inter- and intrapopulation variability, where the development of rediae and cercariae was positively correlated with snail growth.

Department of Biomedical Sciences and Veterinary Public Health Section for Parasitology Swedish University of Agricultural Sciences 750 07Uppsala Sweden

Department of Parasitology Faculty of Science Charles University Vinicna 7 128 44Prague Czech Republic

INSERM U 1094 Faculties of Medicine and Pharmacy 87025Limoges France

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Effect of Fascioloides magna (Digenea) on fecundity, shell height, and survival rate of Pseudosuccinea columella (Lymnaeidae)