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 antar cticus 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 co nfirmed the hypothesis that the distribution and origin of the species is r eflected in a decreasing order of cold hardiness (P. antarcticus > H. spars utum > T. antarcticus) with the sequence reversed in exposures at high temp eratures. The use of such laboratory assessments (supercooling points, uppe r and lower lethal temperatures) when applied to single species and as a co mparative bioassay, is discussed.