Freezing and Survival of Insects at Low Temperatures

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Abstract
The more important literature concerning freezing and conditions determining survival after freezing in plants and animals is cited. The development of studies on cold endurance from simple observations to qualitative experiments, and finally to quantitative experiments is emphasized. The contribution of the author consists of a study of the freezing and undercooling points of 3 ecological groups of insects: (1) aquatic; (2) stored-products, representing a group supposedly tropical or subtropical; (3) oak-borers, representing a group of insects exposed to extremes of high and low temperatures. Among the aquatics, Ischnura, Gomphus, Sympetrum, Leptocella, Phryganea, Neuronia, Buenoa, Belostoma, Notmecta, Cybister, Coptotomas and Dytiscus were studied at each of the seasons. These species averaged together, at all times of the year, showed a freezing point of .57 [plus or minus] .03 and an undercooling point of 1.52[plus or minus] .3. The stored- products pests showed more variation but apparently no seasonal periodicity." Tribolium confuswn Duval adults and larvae, Sitophilius granarius Linn, adults and Pyralis farinalis Linn, larvae were studied. The oak-borers studied were the larvae of Synchroa punctata Neum., Dendroides canadensis Lee, Romaleum rufulum Hald., Elaphidion mucronotatum Fab. and adults of Nyctobates fasciatus Deg. A marked seasonal periodicity correlated with environmental temperature was found with those oak-borers collected out of doors. Cold hardiness increased in winter, only to be lost again in the spring. Moisture contents of the larvae were taken. Cold hardiness was produced experimentally by low temperatures and by dehydration. Conversely, cold hardiness was decreased by exposure to high temperature with high relative humidity. Experiments performed to determine the nature of freezing showed it to be crystalloidal since no hysteresis was observed on repeated freezings and the frozen blood showed well marked crystalline structure. In some insects a secondary freezing point exists below that ordinarily found. Fully hardened insects may survive the 1st freezing but not the 2nd. The freezing of the nervous tissue may be responsible for the secondary freezing point. A bibliography of 57 titles is given.

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