Larval trematode antagonism: principles and possible application as a control method

The main features of trematode antagonism are reviewed briefly, and results of recent field experiments to test whether trematode antagonism can be used for control of trematode infections are discussed. These results show that it is easy to control trematode infections by dispersing large numbers of eggs of a dominant parasite in relatively small bodies of water. Such release may produce a multiple effect: (1) intertrematode antagonism; (2) considerable decrease in the snail population due to higher mortality and parasitic castration of infected snails; and (3) a microsporidan epidemic caused by a hyperparasite, affecting rediae and sporocysts and leading to suppression of cercarial production. Any one or a combination of the three effects may achieve control of the target species. The usefulness of this biological control method depends largely on whether dominant parasites can be found that fulfill the requirements for large-scale application and on whether other factors interfere with antagonism or prevent snails from becoming infected with the dominant speices. A good dominant trematode should be strongly antagonistic to the target species, have a wide geographic distribution, develop rapidly in the snail and cause complete castration, be easily maintained in the laboratory, and preferably be capable of infecting the snail hosts in their various habitats. Development of efficient methods of dispersing eggs and more field experiments are necessary to determine the advantages and limitations of this method.