The snail Biomphalaria glabrata (Say) was infected with two species of echinostomes of Brazilian origin: Paryphostomum segregatumDietz and Echinostoma lindoenseSandground and Bonne. Snails harboring E. lindoense were easily superinfected with P. segregatum. Developing P. segregatum rediae consumed E. lindoense larvae and eventually cleared the snails of this species except for metacercarial cysts. E. lindoense rediae were unable to consume P. segregatum larvae, but they exerted indirect antagonism resulting in delayed development of P. segregatum. Snails simultaneously exposed to the two species of miracidia developed double infections, but E. lindoense larvae were ultimately destroyed in the snails. Snails infected with P. segregatum were difficult to superinfect with E. lindoense. Double infections developed only when the exposure interval was 10 days or less. P. segregatum rediae consumed E. lindoense larvae in these double infections.
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