Studies on the Food and Feeding Habits of Oncomelania quadrasi, the Snail Intermediate Host of Schistosoma japonicum in the Philippines

Among the requirements essential to the existence of Oncomelania quadrasi M6llendorff, suitable food and the feeding habits appear especially significant. In eastern Leyte where the physical and local climatic conditions are apparently the same, only certain restricted areas are inhabited by 0. quadrasi. Pesigan et al. (1958) found that such habitats appear to have the necessary moisture, topography and vegetation. Also, they observed that the soil and water analyses, as well as water level fluctuations, in both areas positive and negative for 0. quadrasi, showed no significant differences. In view of those observations, this study is directed toward an analysis of the food and feeding habits to determine whether these conditions may account for the localized nature in the distribution of 0. quadrasi in Leyte. Some studies of the food and feeding habits of the different species of Oncomelania have been attempted. Mao (1958) investigated the food of Oncomelania hupensis, the intermediate host of Schistosoma japonicum in China. He found that the food of this animal consisted of grasses (Graminae), diatoms (Bacillariophyceae) and ferns (Polypodiaceae). He asserted that the role of the radula of the snail is mainly to take or scrape the food particles and bring them into the buccal cavity without taking part in mastication. Komiya et al. (1957) observed that 0. hupensis feed on mud rich in diatoms (Naviculaceae). They devised a new and simple technique for studying the feeding habits of the animal in that they allowed the snail to crawl on the bottom of a Petri dish which was then inverted and the feeding activity examined under a dissecting microscope. Ritchie (1955) studied 0. nosophora, the intermediate host of S. japonicum in Japan. He found that young snails are not capable of digesting living algae; he also discovered that a blue-green alga, A nabaena, has an undesirable effect on laboratory snails. Wagner and Wong (1956, 1957) in Loma Linda, California, verified the findings of Ritchie and observed that young 0. quadrasi reared in their laboratory fed on soil, leaves, filter paper, molds and algae. None of these investigators, however, dissected snails to examine the stomach microscopically for organic and inorganic contents. This investigation, then, represents the first attempt to study and identify the food of 0. quadrasi and to observe some of its feeding habits.