Physiological Conditions of Cold-hardiness in Insects

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Abstract
The results of the present investigation can be summarized as follows:—1. Cold-hardiness in insects depends on the physiological state of the organism; the most resistant are the phases in diapause (prepupae of Croesus septentrionalis, eggs of Lymantria dispar, pupae of Acronyctinae); not so hardy are the caterpillars of Lasiocampa quercus stopped in their development and prepupae of Agrotis segetum; practically non cold-hardy are developing (or growing) insects, viz., the full-grown larvae of Calliphora erythrocephala, the growing caterpillars of Loxostege sticticalis and Agrotis segetum.2. The difference in the cold-hardiness of these three groups depends on the specificity of their cellular respiration. Growing insects show in their cellular respiration the prevalence of oxydases, the activity of which is connected with characteristics of their cellular structures; in cold-hardy insects the cellular respiration is closely connected with the anoxybiotic processes caused by the dehydrases; their activity is not bound up with the structural elements of the cells, but is closely connected with the presence of non-saturated fat-acids (Dixon, 1929; Meldrum, 1934) peculiar to insect fats.3. The respiration of growing or developing insects is entirely and rapidly destroyed by narcotics, cyanide and low temperatures; the effect of these agents is due to the destruction of the cellular structures. The respiration of cold-hardy insects is characterised by its definite thermostable part and is also resistant to narcotics (or cyanide, Bodine, 1934). Destroying the cellular structures does not affect that respiration. Cold-hardiness increases with the increase of the percentage of thermostable respiration.4. Freezing of the protoplasmic water causes the death of an insect only in the absence of thermostable respiration. Many insects in diapause (characterised by a high percentage of thermostable respiration) can be frozen without any lethal effect (Pyrausta nubilalis, Croesus septentrionalis, Lasiocampa quercus). It is clear that the freezing of the free protoplasmic water cannot be considered as an obligatory cause of “ anabiosis.”5. The quantity of fat does not show any direct connection with thermostable respiration and cold-hardiness in insects. It is probable that the important factor is the quality of the fats, namely, the rôle of non-saturated fat-acids. The increase of cold-hardiness in insects after dehydration can be connected with the changes in cellular respiration; the same can be said regarding the general connection of the water content of the protoplasm and cold-hardiness.