Comparative thermal tolerance of herbivorous and predatory beetles on South Georgia, sub-Antarctic

On the sub-Antarctic island of South Georgia the field distributions of two herbivorous perimylopid beetles Hydromedion sparsutum and Perimylops antarcticus overlap with the latter occurring at higher altitudes. An introduced predatory carabid beetle (Trechisibus antarcticus) is found in the coastal lowlands in close association with H. sparsutum. Laboratory experiments confirmed the hypothesis that the distribution and origin of the species is reflected in a decreasing order of cold hardiness (P. antarcticus > H. sparsutum > T. antarcticus) with the sequence reversed in exposures at high temperatures. The use of such laboratory assessments (supercooling points, upper and lower lethal temperatures) when applied to single species and as a comparative bioassay, is discussed.