Key themes in the study of seasonal adaptations in insects I. Patterns of cold hardiness

Recent work on selected topics of particular interest for understanding insect cold hardiness is reviewed. Themes considered include the dynamic nature of cold hardiness, ice nucleation, connections between cold hardiness and desiccation, rapid cold hardening, seasonal changes in mitochondria, survival in nature, and selection for types of cold hardiness. Such seasonal adaptations have a wider range of components than has often been appreciated, including independently evolved elements. Some specific conclusions are drawn and suggestions are made for future work. Several adaptations, such as rapid cold-hardening and mitochondrial degradation, will probably prove to be much more widespread than has yet been realized. From a general perspective, understanding such diverse components and their differences requires an ecological approach that places the biochemical and timing adaptations in context with habitat conditions and demands related to the stresses of the adverse season, seasons favorable for development and reproduction, and the signals that are available in each habitat to predict future environments. Further understanding therefore depends especially on efforts to analyse the adaptations of individual species in the context of their natural environments.