Diapausing larvae of the midge Aphidoletes aphidimyza (Diptera : Cecidomyiidae) survive at subzero temperatures in a supercooled state but tolerate freezing if inoculated by external ice

Diapausing larvae of Aphidoletes aphidimyza (Diptera: Cecidomyiidae) had relatively low supercooling points (SCP) ranging from -19.0 to -26.4 degreesC. None of the specimens that froze at this temperature survived. A high survival rate (up to 87%) at -10 degreesC for 10 days was observed in supercooled larvae. Such features are characteristic for insects that use a chill-tolerance strategy of cold hardiness. However, the cocoons formed by the diapausing larvae were penetrable by external ice crystals and the larvae showed a relatively high survival rate (23 - 34%) at -10 degreesC for 10 days also in the frozen state caused by inoculation by external ice at high subzero temperatures. Such a duality with respect to cold hardiness strategies seems to be ecologically relevant to overwintering in soil habitats where there may be unpredictable contact with external ice.