THERMAL TOLERANCE LIMITS IN 6 WEEVIL SPECIES (COLEOPTERA, CURCULIONIDAE) FROM SUB-ANTARCTIC MARION ISLAND

Supercooling points, lower lethal temperatures, and the effect of shor t-term exposures to low temperatures were examined during both winter and summer in the adults of six weevil species from three different ha bitats on Marion Island. Upper lethal limits and the effects of short- term exposure to high temperatures were also examined in summer-acclim atized adult individuals of these species. Bothrometopus elongatus, B. parvulus B. randi, Ectemnorhinus marioni, and E. similis were freeze tolerant, but had high lower lethal temperatures (-7 to -10 degrees C) . Seasonal variation in these parameters was not pronounced. Physical conditions of the habitat appeared to have little effect on cold hardi ness parameters because the Ectemnorhinus species occur in very wet ha bitats, whereas the Bothrometopus species inhabit drier areas. The adu lts of these weevil species are similar to other high southern latitud e insects in that they are freeze tolerant, but with high lower lethal temperatures. In contrast, Palirhoeus eatoni, a supra-littoral specie s, avoided freezing and had a mean supercooling point of -15.5 +/- 0.9 4 degrees C (SE) in winter and -11.8 +/- 0.98 degrees C in summer. Sur vival of a constant low temperature of -8 degrees C also increased in this species from 6 h in summer to 27 h in winter. It is suggested tha t this strategy may be a consequence of the osmoregulatory requirement s imposed on this species by its supra-littoral habitat. Upper lethal temperatures (31-34 degrees C) corresponded closely with maximum micro climate temperatures in all of the species. This indicates that the pr onounced warming, accompanied by the increased insolation that has bee n recorded at Marion Island, may reduce survival of these species. The se effects may be compounded as a consequence of predation by feral ho use mice on the weevils.