Ingestion of Ice-nucleating Active Bacteria Increases the Supercooling Point of the Lady Beetle Hippodamia Convergens

Regulation of the temperature at which insects freeze is a critical factor in their overwintering survival. Although the role of ice-nucleating active bacteria in promoting frost-damage in plants is well known, their interaction with other organisms has not been described. In winter. many freeze-susceptible insects avoid freezing by lowering the temperature at which their body fluids spontaneously nucleate, termed the supercooling point. The lady beetle, Hippodamiu conuergens (Coccinellidae, Coleoptera), is a freeze-susceptible insect that overwinters as an adult in the supercooled state, 16°C. In the control group, none of the beetles fed only water had supercooling points above lS”C, similarly no beetles fed an ice-nucleating negative bacterium had supercooling points above 14°C. Following ingestion of the ice-nucleating active bacteria, Pseudomonas syringue and Erwinia herbicolu ( IO9 bacteria/ml), the supercooling point was elevated to -3.5 and -4.4”C respectively, the supercooling point remained elevated for 7 days after P. syringae treatment and a dose-response relationship was observed. Key Word Index: Pseudomonas syringae; Erwinia herbicola; Hippodamia convergens; supercooling point; ice-nucleating agents