CHEMOATTRACTION AND PENETRATION OF ECHINOSTOMA-TRIVOLVIS AND ECHINOSTOMA-CAPRONI-CERCARIAE IN THE PRESENCE OF BIOMPHALARIA-GLABRATA, HELISOMA-TRIVOLVIS, AND LYMNAEA-ELODES DIALYSATE

A petri-dish bioassay was used to study the chemoattraction and penetr ation of the cercariae of Echinostoma trivolvis and E. caproni in the presence of snail dialysates from Helisoma trivolvis (Pennsylvania and Colorado strains), Biomphalaria glabrata, and Lymnaea elodes. Signifi cant chemoattraction was seen with E. trivolvis cercariae in the prese nce of all snail dialysates released from nonperforated dialysis sacs with a molecular-weight exclusion of 12,000. Under the same conditions , E. caproni was significantly attracted to B. glabrata and H. trivolv is (CO strain) but not to L. elodes or H. trivolvis (PA strain). Dialy sis sacs were perforated with needles to allow the release of snail su bstances of all molecular weights into the bioassay. Cercariae of both species were significantly attracted to all snail dialysates released from perforated sacs. Moreover, cercariae entered these sacs and pene trated the snails, and 24 h later the percentage of cysts per snail sp ecies ranged from 70% to 83% for E. trivolvis and from 73% to 93% for E. caproni. Dialysates released from intact sacs were extracted in cho loroform-methanol (2:1) to obtain hydrophilic and lipophilic fractions . When these extracts were placed on agar plugs in the bioassay, the l ipophilic fraction, but not the hydrophilic fraction, was mainly chemo attractive.