Ice-Nucleating Active Bacteria Reduce the Cold-Hardiness of the Freeze-Intolerant Colorado Potato Beetle (Coleoptera: Chrysomelidae)

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Abstract
In laboratory experiments, a freeze-dried concentrated form of the icenucleating active bacteria, Pseudomonas syringae, was used to decrease the supercooling capacity of field-collected diapausing Colorado potato beetles, Leptinotarsa decemlineata (Say). Application of the P. syringae to adult beetles increased their mean supercooling point values from −7.6 ± 0.2°C (untreated) to −3.7 ± 0.1°C (1,000 ppm). No beetles survived cooling to temperatures below their supercooling point, indicating that this species is freeze-intolerant. During tests conducted in 1991 and 1992, the increase in the supercooling point was directly dependent on the amount of P. syringae added to soil containing the beetles. Cumulative freezing distributions indicated that 80% of beetles treated with 100ppm of P. syringae would be expected to freeze and die when exposed to −5°C; in contrast, none or very few of the untreated control beetles would be expected to freeze at this temperature. Other experiments demonstrated that the capacity of P. syringae treatments to increase the supercooling point of the beetles decreased after 2 wk of exposure at 4°C and when experiments were done at 10°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 conjunction with cultural control strategies for increasing winter mortality.

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