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In preparation for winter many insects enhance the supercooling capacity of their body fluids by 25°C or more, thereby avoiding the lethal effects of tissue freezing. A primary factor limiting supercooling capacity is the presence of nucleating agents that catalyze ice formation at high subzero temperatures. Two species of ice nucleating active (INA) bacteria, Enterobacter agglomerans and Enterobacter taylorae, the latter with previously unknown ice nucleating activity, were isolated from the gut of two species of field-collected beetles, Ceratoma trifurcata and Hippodamia conuergens. Ingestion of these INA bacteria greatly diminished the capacity of our insect model, H. convergens, to supercool and caused freezing at temperatures as high as -15°C. Removal or masking of endogenous INA bacteria may be a major factor in the cold-hardening of freeze intolerant insects for winter survival. Furthermore, these bacteria may provide a novel biological insecticide to control overwintering pest insects by decreasing their natural capacity to supercool.

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