No abstract

Three species of land snails, Theba pisana (Müller, 1774), Cernuella virgata (Da Costa, 1778) and Cochlicella acuta (Müller, 1774), introduced to Australia from the Mediterranean region, cause significant economic problems in harvested crops in southern Australia. One of the strategies for post-harvest control of these snails involves stubble management to knock the snails onto the hot ground during summer. Farmers report variable results with this strategy, which could be due to varying heat tolerances between the 3 species. In a series of laboratory experiments, field-collected snails of the 3 species were tested for their ability to survive high surface temperatures for varying periods of time. The results reported here indicate differences between the 3 species in their tolerance of soil surface temperatures, and suggest that the variable results noted in the field are due at least in part to the differing heat tolerances of the 3 species. When adult snails were placed in incubators at a constant temperature, all T. pisana died after 3 h at 55°C, while C. virgata and C. acuta survived longer, with 100% mortality only after 2 successive 6-h exposures at 55°C. Weight loss of snails was measured after heat treatment to estimate water loss under these conditions. Recommendations are made for more effective mechanical control strategies for snails in the field during summer.

No abstract

The effects of osmotic stress on water loss and subsequent desiccation survival of Anguina funesta second stage juveniles (J2), Rhabditis strongyloides (J2-J4), Aphelenchus avenae (J2-adult) and Heterorhabditis bacteriophora (J3) were investigated by incubating nematodes in sucrose gradients before exposure to 0% relative humidity (RH). Survival of A. funesta J2 was unaffected by osmotic stress and subsequent desiccation and juveniles seemed pre-adapted to both forms of dehydration. Heterorhabditis bacteriophora showed high tolerance to osmotic stress but all J3 were killed by exposure to 0% RH. Pre-exposure to osmotic stress improved desiccation tolerance in R. strongyloides and A. avenae but the stress levels that induced protective adaptations against desiccation were different for each species. Osmotically induced water loss was rapid in all four species and nematodes reached equilibrium after 4-12 h, their nal water content being dictated by the osmotic pressure of the medium. A unique mechanism of osmotic adaptation occurred in R. strongyloides J2-J4 allowing juveniles to regain their initial hydration level.