Snail Control in Trematode Diseases: the Possible Value of Sciomyzid Larvae Snail-Killing Diptera

Abstract

This chapter focuses on a family of true flies or Diptera, the Sciomyzidae or marsh flies, whose larvae kill and feed upon pulmonate snails. Larvae of more than 100 species in this family have destroyed freshwater and terrestrial gastropods in laboratory trials. More than 80 species have been reared from hatching to pupation solely on snails, introduced alive into their rearing dishes. Laboratory trials against important hosts of human blood flukes from various parts of the world indicate that the hosts of Schistosoma mansoni Sambon are very vulnerable to attacks by these larvae, that the Bulinus species that transmit S. haematobium (Bilharz) are less so, and that Oncomelania, hosts of S. japonicum Katsurada, are invulnerable. Laboratory and field tests of Sciomyzidae experimentally introduced into Hawaii, Guam, and Australia for a control of fascioliasis also are discussed. Academic and theoretical consideration suggests that the sciomyzid flies are one of the several groups that may be of practical value in the biological control of fluke-bearing snails and that much more effort should be expended in the quest for other natural enemies of snails and in research into their potential value as agents of biological control. Although all sciomyzid larvae probably kill gastropod mollusks, remarkable differences in their habitats, adaptations, modes of attack, and choices of food snails are indicated and described. The known larvae form a behavioral and morphological continuum that may indicate the course of evolution. Parasitologists seem agreed that control of the snail intermediate host is one effective means of reducing the transmission rate of trematode diseases. Methods of snail control, such as biological and integrated control methods, are elucidated.