SOIL FACTORS INFLUENCING THE DISTRIBUTION OF ONCOMELANIA-QUADRASI, THE INTERMEDIATE HOST OF SCHISTOSOMA-JAPONICUM, ON BOHOL-ISLAND, PHILIPPINES

Soil conditions essential to the survival of Oncomelania quadrasi on B ohol Island in the Philippines were examined to clarify the factors li miting distribution of the snail and to develop a method for breeding large numbers of the snail in the laboratory. Soil samples in and arou nd snail habitats were analysed and used for breeding experiments in t he laboratory. Experiments using paddy soil derived from different par ent materials revealed that the numbers of juvenile snails hatched var ied widely between several soil samples. The best soils for reproducti on generally had a pH of 5.6-7.9 and > 200 mg of available CaO/100 g. These soil factors, in addition to shade and moisture, determine the o ptimum conditions for the breeding of O. quadrasi in the field as well as in the laboratory. The determination of the optimum conditions for laboratory breeding of O. quadrasi and other intermediate snail hosts should facilitate detailed study of the hosts and the development of better methods to control or eradicate schistosomiasis and other snail -transmitted diseases.