ABSTRACT
The resistance exhibited by insects to high temperatures depends on the interaction of at least three factors: length of exposure, relative humidity, and behavior. However, during the summer, temperatures in sunny areas at ground level can easily surpass the ants' limits of tolerance. The red imported fire ant, S. invicta, does not have any known unusual physiological adaptations to cope with temperature extremes and differs little from the native fire ants of North America in heat tolerance and supercooling points. Cold-hardiness in insects encompasses three distinct phenomena: cold acclimation, supercooling, and freeze tolerance. Cold acclimation usually involves seasonal changes in metabolites correlated with depressed supercooling points or freezing tolerance. The northern limits of distribution of S. invicta in North America seem to be determined by its tolerance to cold temperatures. Thus, colder temperatures and the duration of winter, both of which progressively increase further north, have a significant negative impact upon imported fire ant populations.
