Anatomic site of application of ice-nucleating active bacteria affects supercooling in the Colorado potato beetle (Coleoptera: Chrysomelidae)

Abstract

Most overwintering insects do not survive internal freezing and must avoid low temperatures or enhance the capacity of their body fluids to supercool to survive low temperature exposure. Recent reports have demonstrated that the application of ice-nucleating active microorganisms markedly diminishes supercooling. Topical application of as little as 20 ppm of a suspension of a freeze-dried preparation of the ice-nucleating active bacterium Pseudomonas syringae van Hall was sufficient to elevate the mean supercooling point of the overwintering adults of the Colorado potato beetle, Leptinotarsa decemlineata (Say), from −8.7 to −4.7°C. Previous reports have demonstrated that topical application of these biological ice nucleators to insects whose mouths have been sealed still reduces supercooling capacity; however, the anatomical route by which these agents make contact with body water is unclear. Application of the P. syringae suspension to the ventral abdomen did not significantly increase the supercooling point (−5.5°C) compared with beetles treated with the non-ice-nucleating active (control) bacterium Escherichia coli (Migula). However, application of the ice-nucleating agent to the thoracic spiracle, ventral cervix, or abdominal spiracle elevated supercooling point values above those of beetles treated on the ventral abdomen. These data are instructive in the development of methods for the use of ice-nucleating active microorganisms for the biological control of overwintering pests.