Heat tolerance of Mediterranean land snails under induced dormancy in South Australia

Exotic pests associated with international trade are a major concern worldwide (Drake et al., 1989, Biological invasions: A global perspective ; Campbell, 2001, Bioscience , 51:148–153). Invasive pests damage ecosystems, agriculture, forestry and the economy (Pimentel et al., 2001, Agriculture, Ecosystems & Environment , 84:1–20). The current option to treat exotic molluscs at Australian borders is methyl bromide fumigation (128 ppm [g/m 3 ], 24 h). Dry heat treatment trials have been conducted with different land snail species but there is a lack of research on temperatures and exposure periods that effectively kill the most heat tolerant species of land snails at their most heat tolerant life stage. Elevated temperatures are predicted to efficiently kill Mediterranean snail species Cernuella virgata (Da Costa, 1778) and Theba pisana (Müller, 1774), but lethal temperatures and exposure period combinations are not known for these snails, particularly at different development stages and during dormancy. The aim of this study was to determine the temperature and exposure duration required to induce mortality in the heat tolerant snail species C. virgata and T. pisana. We hypothesise that snails held dormant in tins for longer periods exhibit higher thermal tolerance, requiring longer heat exposure for mortality. Snails were collected, loaded into tins 2, 4 and 6 weeks prior to treatment and kept undisturbed without food and water to induce dormancy. Tins containing snails were exposed to 50°C, 55°C and 60°C temperatures for exposure periods at intervals between 15 and 180 min, with controls kept at ambient temperature. T. pisana were able to survive for 3 h at 50°C and 2 h at 55°C. Heat treatment at 60°C for 1 h was found to control both snail species tested. A significant relationship was found between longer dormancy and heat tolerance when T. pisana were treated at all temperatures, particularly at 55°C ( p < .001). The results from this project support the development of a scientifically based dry heat treatment protocol to effectively control the most heat tolerant species of invasive snails intercepted during international trade.