The ecophysiology of apple snails in rice: implications for crop management and policy

This review relates the ecology and physiology of apple snails (Ampullariidae) to their impact on rice-production systems. Two species in particular, Pomacea canaliculata and Pomacea maculata, have been introduced to several rice-growing regions. Flooded rice systems represent a high-quality habitat for these apple snails because of similarities in the environmental conditions (water temperature, salinity, pH, water flow velocity) necessary for both rice production and for snail survival and development. Furthermore, amphibious respiration, a capacity to aestivate during dry periods, as well as cold acclimation and tolerance (particularly in P. canaliculata), increases the resilience of apple snails to rice farming practices, including agrochemical applications, intermittent drainage and crop rotations - under a wide range of climatic conditions. Risks to regional rice production depend on four principal factors: these are (a) regional climate, (b) regional rice-production systems, (c) prevailing production practices, and (4) the presence/absence of invasive, non-native apple snails. Based on these criteria, lowland irrigated rice in tropical and subtropical regions that is wet-direct seeded is most vulnerable to damage from both native and non-native apple snails (albeit with greater losses from non-native snails because of normally higher densities). Adequate quarantine regulations, particularly in vulnerable tropical regions that are adjacent to centres of recent outbreaks (e.g. India and Bangladesh adjacent to Myanmar, Peru and Colombia adjacent to Ecuador) and attention to the preparedness of farming systems could reduce potential impacts as these highly invasive snails continue to spread. The urgent development of labour-saving crop-establishment methods that reduce dependencies on chemical molluscicides is necessary to achieve sustainable rice production in regions at risk from non-native apple snails.