Philophthalmus gralli: chemosensitivity of miracidia

The responses of Philophthalmus gralli miracidia to various chemicals stimulative to other miracidial species were tested by contact and return (CR) to agar blocks containing chemicals and aggregation near a point inoculum in phi-chambers. Of a series of amino acids, glutamic and aspartic acid elicited the greatest responses in both tests, which were similar to that observed with snail-conditioned water. Sialic, acetic, hydrochloric, and sulfuric acids gave high percent CR at all concentrations tested but required higher levels to stimulate a significant miracidial response in phi-chambers. Miracidia were slightly responsive to Mg++ and ammonia in CR tests but only showed a significant reaction to 1.0 mM ammonia in phi-chambers. Attachment responses to the agar blocks by miracidia were noted at the higher concentrations of all chemicals tested except MgSO4 and NH4Cl. At 25 and 50 mM H2SO4 and HCl, contact with the agar block proved lethal to the miracidia. Miracidial behavior was klinokinetic rather than chemotactic in both test systems.