Studies on the temperature dependence of activity and on the diurnal activity rhythm of the invasive Pomacea canaliculata (Gastropoda: Ampullariidae)

Abstract

> Abstract The South American apple snail Pomacea canaliculata is invasive in Asia and in the USA. In the fi rst part of the present study, the effect of temperature on the activity of these gastropods was studied in experimental aquaria with water tempera- tures ranging from 20°C to 32°C. Overall, activity was shown to increase with temperature. Moreover, crawling velocity was also shown to be positively correlated with temperature. We conclude that the geographic expansion of P. canaliculata could be facilitated by a warmer climate. In the second part of the present study, the diurnal activity rhythm and vertical movement was analysed under condi- tions of a 12L : 12D photo period and at a constant temperature of 26°C. Pomacea canaliculata showed higher activity during the hours of darkness. The diurnal activity increased during 1-2 hours after onset of darkness, followed by a plateau of high activity, then declined a few hours before the onset of light. A relatively constant and intermediate level of activity was observed during the hours of light. Similarly, vertical movement of the animals proved dependent on time of day. We hypothesise that the observed activity rhythms represent an adaptation to avoid specialised predators in the native range of P. canaliculata. Our fi ndings can contribute to optimise pest management strategies.