Influence of low temperatures on the cercarial shedding of Paramphistomum daubneyi from the snail Lymnaea truncatula

Abstract

Lymnaeids in nature are subjected to temperature fluctuations that may have an influence on the shedding of cercariae. Thus, experimental infections of Lymnaea truncatula by Paramphistomum daubneyi were performed to determine whether a sudden fall in temperature - daily dipping of infected snails into spring water at 14-15°C, or at 6-8°C - followed by its increase at 20°C in the subsequent hour, had an influence on the characteristics of snail infection and cercarial production. The immersion of infected snails in cold water during a short period delayed the first cercarial shedding, at day 66 on average, in the 6-8°C group vs at day 57 in the 14-15°C group, or at day 49 in the 20°C group. The percentage of cercaria-shedding snails was greater in the 6-8°C group than in the 14-15°C and the 20°C ones : 41.8 % vs 17.3 % and 7.1 %, respectively. The total number of cercariae given by each infected snail was also higher in the 6-8°C group. A fall in the temperature of water during daily change, followed by its increase at 20°C within the subsequent hour, stimulated the cercarial shedding of P. daubneyi.