Abstract
Population census of the apple snail, Ampullarius insulanis D'ORBIGNY, an invading pest that causes serious damage to lowland crops including the rice plant in southern Japan, was conducted in a paddy field at Fukuoka, in 1985. The average number of egg-masses per square meter was 0.4. Average size of the egg-mass was 91.6 and definitely small as compared with that sampled from the water grass in an adjacent irrigation canal i.e. 528.8 on an average. The number of snails per square meter was 12.1 and 19.1, on September 2 and October 4, respectively. Snails with a shell height of more than 30 millimeter, which are recognized as the adult snails, accounted for 4 and 2 percent of the total number on September 20 and October 4. Snails less than 20 millimeter high accounted for 93 percent, on September 20, and 96 percent on October 4. The distribution pattern of both eggs and snails in the paddy field was considered to be contagious. On the basis of the results obtained in this census, no definite correlation between the number of egg-masses and the population of the snails in each census quadrat was recognized.
