Snow white and the seven dwarfs: A multivariate approach to classificationof cold tolerance

Two main cold hardiness strategies of insects - freeze tolerance in some sp ecies, and overwintering in a supercooled state without tolerance of freezi ng in many others - were recently reclassified. However, I present several problems with the current systems. My suggested classification is based on clearer definitions of the causes of cold injury. I recognize three main mo rtality factors: freezing of body liquids, cold shock, and cumulative chill injury. Presence or absence of each of these factors produce eight combina tions. I have named the eight classes after Snow White and the Seven Dwarfs to avoid nomenclatural confusion. Some of these classes are probably not u sed as tactics against cold injury by any insect species. Other classes con tain so many species that they might be reclassified in more detail, using values of supercooling point and other quantitative parameters. However, wi dely comparable parameters, like the upper limit of cold injury zone and th e sum of injurious temperatures are still rarely published, thus we still l ack comprehensive data for multivariate analyses. Every cold hardiness stra tegy should be characterized by a meaningful class or subclass together wit h the physiological, biochemical, and behavioural mechanisms employed by th e insects. I also point out the existence of strategies that combine two ta ctics - either a switching strategy (during preparation for winter, populat ion "chooses" which tactic will be used), or a dual strategy (individuals a re ready to use one of the tactics depending on the prevailing environmenta l conditions).