Emergence of the apple snail, Pomacea canaliculata (Gastropoda: Ampullariidae), after irrigation in a paddy.

Abstract

We investigated the emergence of the overwintering apple snail, Pomacea canaliculata, from paddy soil after irrigation in a rice paddy in Kumamoto Prefecture, Japan. Prior to irrigation, densities of the snails, which were estimated by examining soil samples from the paddy, were 1.8/m2 and 10.0/m2 for live and dead snails, respectively. The proportion of live snails was 0.153, which may represent the survival rate throughout the overwintering period. After irrigation, we surveyed the snails emerging in 12 enclosures (pens) of 2 m×8 m constructed in the paddy. A mean of 27.8 snails per pen was found within the first five days after irrigation, and 3.5 per pen were captured in the subsequent 16 days. Thus, most of the snails emerged rapidly, within five days after irrigation; this period of emergence is far shorter than past records. The shell height of live snails collected after irrigation ranged from 4.9 to 25.8 mm, with a mean of 11.5 mm, which was significantly larger than that of dead snails, suggesting a higher mortality of smaller snails during the overwintering period.