Abstract
The freshwater apple snail Pomacea canaliculata has become a major crop pest in southeast Asia and Hawai'i and threatens natural wetland habitats in these regions and elsewhere. Deliberately introduced as a potential human food resource, it has also been proposed as a possible biocontrol agent against aquatic weeds. Various factors may facilitate its rapid invasion of new areas; we focus on two: growth rate and food preference. Our field observations and laboratory experiments suggest that in Hawai'i P. canaliculata reaches reproductive maturity in 10 months or more, less time than in its native temperate and seasonal Argentina, where it takes 2 years, but longer than in parts of southeast Asia, where it may take as little as 2 months. This increased growth rate, and thence reproductive rate, probably facilitate rapid population growth. Although P. canaliculata is usually considered an indiscriminate generalist macrophytophagous feeder, laboratory experiments indicated preferences among the dominant plants at our field site and growth rate differences when constrained to feed only on one of these plants. Water hyacinth (Eichhornia crassipes), a major invasive weed, was not preferred in food choice experiments, and snails offered only water hyacinth on which to feed did not differ in growth rate from unfed snails. Another important invasive weed, water lettuce (Pistia stratiotes), was also not preferred, but snails fed on it did grow, though not as quickly as those fed on green-leaf lettuce. Among the food plants offered in the experiments the native Vigna marina was the most preferred. Therefore, although a generalist, P. canaliculata exhibits some discrimination among food plants. We recommend that it not be introduced for use as a biological control agent for aquatic weeds.