What is cold hardness in insects?

Cold  hardness is the ability of insects to survive when expose to low temperature.
Insects can first tolerate winter temperature if they first undergo physiological preparedness. The acclimatization process occurs when insects first are eposed to low temperatures which trigger the accumulation of cryoprotectants. A short term exposure to cold temperature to cold temperature can also predict some insects from subsequent lethal temperatures.
TWO PHYSIOLOGICAL STRATEGIES ADOPTED BY INSECTS OVERWINTER:
1. Freezing tolerance
2. Freezing avoidance                                            
FREEZE TOLERANCE
Freeze tolerant insects are the most cold hardy species and found mainly in parts of the world with the harshest winter climate. In most freeze tolerant species, ice nucleating agents (INAs) which are synthesised in the late autumn and early winter acting as sites of freezing to promote safe extracellular freezing at elevated subzero temperatures, usually between -5 degree Celsius and -10.
INAs can be active in the haemolymph or other parts of the body.
Once frozen, freeze tolerant insects can be coed to very low sub-zero temperatures (to -40 degree celsius and -80), which in most cases would be below the SCP of freeze avoiding species. They also contain polyols such as glycerol, which enable the insects to supercoo before the INAs become fully active, and cyroprotect the partially frozen tissues after freezing and antifreeze proteins, which may also provide a back up system to avoid freezing in the   autumn and spring.

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