Decrease in density of the apple snail Pomacea canaliculata (Lamarck) (Gastropoda: Ampullariidae) in paddy fields after crop rotation with soybean, and its population growth during the crop season

We compared the densities of the apple snail, Pomacea canaliculata, between fields that had been planted with soybean or rice in the previous summer. The densities of overwintered snails soon after irrigation at the beginning of rice planting were all very low in the fields after soybean. These values were much lower than the control threshold for the apple snail in direct seeding. Therefore, crop rotation with soybean seems to be a good economic measure to control the apple snail in direct seeding. The snail populations increased very rapidly in both types of fields, in particular, after soybean. Within two and a half summer months, the snail densities in the fields after soybean reached almost the same level as those in the fields after rice. This rapid population recovery in fields after soybean seems to be caused by density-dependent growth and reproduction in this species.