Some Factors Influencing Egg Laying in Oncomelania Nosophora and Oncomelania Quadrasi, Intermediate Hosts of Schistosoma Japonicum

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  • School of Tropical and Preventive Medicine, College of Medical Evangelists, Loma Linda, California


The egg-laying habits of Oncomelania nosophora and O. quadrasi were observed experimentally at 3 temperatures over a 12-month period. It was noted that:

  1. 1.Most (84.5%–91%) of the eggs of O. nosophora were laid in soil, while those of O. quadrasi were laid largely on objects such as brick, gravel and saucer wall.
  2. 2.A medium water level (1/3 saucer capacity) in the rearing saucers resulted in better snail reproduction than at the high (flooded) or low (moist) level.
  3. 3.At 26°C. egg laying started earliest and more eggs and young were found than at 20° or 32°C. Of these last two temperatures, the better results were obtained at 20°C.
  4. 4.Snail mortality was lowest at 20° and highest at 32°C. Adverse culturing conditions developed more rapidly in the saucers kept at 32°C. than at the other two temperatures.
  5. 5.The majority of the eggs were laid above the water line. For O. nosophora the percentage is 94, and for O. quadrasi the percentage is 71.