Studies on Eradication of Intermediary Host of Liver Fluke

Abstract

In order to eradicate the intermediary host of the liver fluke, the agent PCP and copper sulfate were examined in vitro for snail-killing effect. Particularly such working conditions as temperature, time, and degree of growth of snails were compared between the two chemicals. Then fielh trials were conducted by using a method which was considered to be the most practical. The results obtained are summarized as. follows.
1. When administered for full 24 hours at 20 to 25°C, PPC and copper sulfate killed mature snails 100 per cent at a concentration of 1 and 2ppm, respectively. The shorter the period of administration, the higher concentration was needed for effective control of snails. Besides, young snails were inferior to mature ones in resistance. The resistance of the snail seemed to be the strongest at 20 to 25°C.
2. To obtain a snail-killing rate higher than 90 per cent by spraying the agent for 24 hours, it was sufficient to administer 1ppm of PPC and 2ppm of copper sulfate simultaneously. However, a concentration of more than 10ppm was required for either agent to display the same effect by the administration of a single agent.
3. In the field trial, 10g of PPC and 20g of copper sulfate per 1, 000m² were sprayed in the paddy field from which the water had been removed. After the spraying, water was introduced into the paddy field so that the field might be covered again with water at the depth of about 10cm. In this manner a snail-killing rate higher than 90 per cent was obtained without giving any ill effect on the rice cron.