Seasonal changes in populations of Gyrinicola batrachiensis (Walton, 1929) in wild tadpoles

Five hundred and thirty-five tadpoles of Rana clamitans, collected from a permanent pond throughout spring, summer and fall, 1976 to 1978, and 85 tadpoles of Bufo americanus, collected from a seasonal marsh in summer, 1978 were examined for the presence of Gyrinicola batrachiensis. Rana clamitans laid eggs in June or July, passed one winter in the tadpole stage, and metamorphosed the following June or July. Gyrinicola batrachiensis occurred only in tadpoles and was lost from metamorphosing tadpoles prior to the eruption of the forelimbs. Individual female worms produce thick-shelled eggs involved in transmission as well as thin-shelled, autoinfective eggs. The number of each egg type in female worms collected from August 1977 to June 1978 was determined. Young-of-the-year tadpoles apparently were infected by ingesting thick-shelled eggs. In late fall almost all tadpoles contained adult worms and thin-shelled eggs predominated in female worms at this time. There was no transmission or autoinfection in winter; female worms which had wintered in tadpoles deposited autoinfective thin-shelled eggs in April resulting in a sharp increase in intensity. Females of the autoinfective generation matured in May and June, and contained almost exclusively thick-shelled eggs. Thus, young-of-the-year tadpoles enter an environment recently contaminated with thick-shelled eggs of G. batrachiensis. Bufo americanus hatches and metamorphoses in a single season. In this host, G. batrachiensis underwent a single generation. Males were not found and females contained only thick-shelled eggs. The absence of autoinfective eggs in worms from this host is understandable because of the brief period toads spent as tadpoles.