Ice-nucleating active bacteria: a novel approach to the management of the red imported fire ant

Overwintering strategies are important in the survival of insects, and one such strategy involves the regulation of temperatures at which they freeze. Although all insects exhibit some degree of cold tolerance, they can generally be classified as either freeze tolerant or intolerant. Many freeze-intolerant insects seasonally depress their supercooling points, thereby increasing their cold-hardiness in preparation for winter. This study was conducted to assess the influence of cold acclimation on the supercooling ability of the red imported fire ant, Solenopsis invicta Buren. Colonies were consecutively exposed for seven days to decreasing temperatures of 10°, 5°, and O^C (treatments). At the end of each seven-day interval, a thermocouple probe was used to determine whole body supercooling points of randomly selected worker ants from each colony. In addition, head capsule widths and whole body weights were measured. Analysis of variance indicated a significant difference among supercooling points and acclimation temperatures (£ < 0.05).

In the 1970's, ice-nucleating active bacteria, a new category of biological ice-nucleators, were discovered among other epiphytic bacteria living on the surface of plants. These ice-nucleating bacteria have the capacity to catalyze ice formation at - 1° to -2°C. I therefore studied the effects of topical mist application of the ice-nucleating active bacteria Pseudomonas syringae (American Type Culture Collection 39254) on the freezing point of minor and media worker ants. My results showed that treatment with P. syringae increased the temperature at which the red imported fire ant froze, thus decreasing its supercooling ability (NOVA; P < 0.05).