TROPISTIC BEHAVIOR IN SCHISTOSOMIASIS: MIRACIDI AND CERCARIAE PREDATORS.

Some aspects of the behavior of Schistosoma mansoni cercariae were investigated. A linear relationship between temperature and the speed during upward displacement of cercariae was found for the range from 8 to 40C. Most of S. mansoni cercariae are shed by infected B. glabrata within a daily 6-hour period. The peaks of emergence were found to be between 9 a.m. to 11 a.m. and 1 p.m. to 3 p.m. at San Juan and Belo Horizonte, respectively. The emergence rhythm is environmental dependent exogenous rhythm. The rhythm is suppressed when infected snails are kept in the dark and under constant temperature. The rhythm is kept when infected snails are maintained under constant temperature but subjected to the cyclic diurnal variation of light. The rhythm is also maintained under cyclic diurnal temperature variation although the snails remain in darkness. The rhythm can be reversed by the inversion of the light-darkness periods as well as by the inversion of the daily cyclical temperature variation. Preliminary observations on the radiation effect on infected snails are reported. Author