ICE-NUCLEATING ACTIVE BACTERIA REDUCE THE COLD-HARDINESS OF THE FREEZE-INTOLERANT COLORADO POTATO BEETLE (COLEOPTERA, CHRYSOMELIDAE)

In laboratory experiments, a freeze-dried concentrated form of the ice -nucleating active bacteria, Pseudomonas syringae, was used to decreas e the supercooling capacity of field-collected diapausing Colorado pot ato beetles, Leptinotarsa decemlineata (Say). Application of the P. sy ringae to adult beetles increased their mean supercooling point values from -7.6 +/- 0.2-degrees-C (untreated) to -3.7 +/- 0.1-degrees-C (1, 000 ppm). No beetles survived cooling to temperatures below their supe rcooling point, indicating that this species is freeze-intolerant. Dur ing tests conducted in 1991 and 1992, the increase in the supercooling point was directly dependent on the amount of P. syringae added to so il containing the beetles. Cumulative freezing distributions indicated that 80% of beetles treated with 100 ppm of P. syringae would be expe cted to freeze and die when exposed to -5-degrees-C; in contrast, none or very few of the untreated control beetles would be expected to fre eze at this temperature. Other experiments demonstrated that the capac ity of P. syringae treatments to increase the supercooling point of th e beetles decreased after 2 wk of exposure at 4-degrees-C and when exp eriments were done at 10-degrees-C. If delivery systems were developed that would expose adult beetles to ice nucleating agents and preserve their ice nucleating activity until critical low-temperature exposure occurs in mid-winter, these nucleating agents could be used in conjun ction with cultural control strategies for increasing winter mortality .