[Dynamics of infection of Bithynia tentaculata (Gastropoda: Prosobranchia) with trematodes].

The dynamics of infection of Bithynia tentaculata with 7 trematode species was examined during 5 years. Stability of parasite fauna with significant changes of infection rate has been recorded. During the period of observations the infection rate of Sphaeridiotrema globulus, Notocotylus imbricatus, Holostephanus volgensis, Pleurogenoides medians and Metorchis intermedius has decreased, while that of Psilotrema tuberculata has increased. The infection rate of Plagiorchis sp. slightly fluctuated. It was found out that the infection rate of S. globulus, P. tuberculata, Plagiorchis sp., H. volgensis and M. intermedius increases by the age of hosts. Maximal infection rate of N. imbricatus was observed in mollusks of 2-3 years old. Based on peculiarities of infection dynamics during the year, 3 groups of parasites have been recognized. 1. S. globulus, P. tuberculata and N. imbricatus show an increase of infection rate from April to August with subsequent decrease. 2. Infection rate of H. volgensis increases during the Summer and reaches maximum in Autumn. Age group of host 2+ and older ones showed some decrease of infection in the beginning of Summer. 3. First cases of infection with M. intermedius occur in May, then the infection rate increases and reaches maximum in the end of July. The infection rate gradually decreases and in the end of October the mollusks infected with M. intermedius are usually absent. An emission of cercariae is usually observed in June-August. The difference in infection rate of Bithynia tentaculata males and females was not found. Based on a complex analysis of infection dynamics and population dynamics of mollusks, different aspects of the life cycle of parasites (periods of emission, maturity and longevity of local microhemipopulations) are discussed.