Effect of ice-nucleating bacteria (Pseudomonas syringae Van Hall) on insect susceptibility to sub-zero temperatures

Many stored product insect pests are termed "freeze-intolerant" because they cannot survive ice formation in their extracellular body fluid. In grain silos, the progressive decrease in temperature permits the acclimation of insects and enhances their cold tolerance. The objective of this study was to examine the influence of the concentration of the ice-nucleating-active bacterium Pseudomonas syringae (10, 100 and 1000 ppm), temperature and duration of sub-zero exposure on the cold tolerance of the granary weevil Sitophilus granarius (L.) and the saw-toothed grain beetle Oryzaephilus surinamensis (L.). After an application of 1000 ppm of powdered P. syringae to grain, the mortality of S. granarius and O. surinamensis was increased after 24-h exposure to -4 degrees C. Higher mortality was observed after exposure to colder temperatures and a dose-response relationship was evident. At near-zero (-4 to 0 degrees C) negative temperatures, no dose response was observed, and the mortality in treated grain was the same as that in untreated grain. (C) 1998 Elsevier Science Ltd. All rights reserved.