Meeting Abstract

50.1  Monday, Jan. 5  Supercool social wasps: lower lethal limits to cold tolerance CORRIGAN, S.T.*; IRWIN, J.; Central Wash. Univ. corrigas@gmail.com

Of the selective pressures that have shaped species evolutionary success or failure, the most universal abiotic factor, is probably temperature. In the higher latitudes the ability to survive cold temperatures may be the limiting factor to historical species radiation, distribution and abundance. Because insects are the most diverse fauna on earth, inhabiting the planet from pole to pole, the study of insect cold tolerance has received increased scrutiny. In temperate regions of North America, such as eastern Washington State, overwintering queens of the social wasps (Hymenoptera: Vespidae), the yellowjackets and paper wasps, must survive sustained sub-zero winter temperatures. Because freezing of intracellular fluids invariably causes damage to cell membranes, it is usually lethal to the organism. To ascertain the lethal limits to low temperature survival of vespid wasps, we measured the supercooling points (SCPs) of gynes from four species representing three genera of locally occurring social wasps. In all cases, a seasonal progression in cold hardening was observed; as fall advanced into winter, supercooling ability increased, resulting in progressively lower SCPs. Though data in some cases indicated differences between genera, we found that most local wasps in the heart of winter are able to survive at least brief exposures below -20C. Mean midwinter SCPs were as follows: Dolichovespula maculata , -20.1; Vespula pensylvanica, -22.3; Vespula germanica, -22.6; Polistes dominulus, -23.3. No wasp in our study survived freezing, even those inoculated by external ice. Our data indicate that the vespid wasps in eastern Washington State are not tolerant to freezing, and instead survive winter by the ability to supercool below temperatures that are generally experienced in hibernacula.