THE EFFECT OF HIGH-TEMPERATURE STORAGE ON THE CAPACITY OF AN ICE-NUCLEATING-ACTIVE BACTERIUM AND FUNGUS TO REDUCE INSECT COLD-TOLERANCE

Cold treatment is used to control the rusty grain beetle (Clyptolestes ferrugineus) (Coleoptera: Cucujidae), the predominant insect pest of stored grain in Canada. However, because it is difficult to cool the grain enough to control C. ferrugineus quickly, we have examined ways to reduce the cold-tolerance of adult C. ferrugineus, the most cold-hardy stage. We compared the efficacy of two ice nucleators, Pseudomonas syringae and Fusarium avenaceum, to decrease cold-tolerance of this insect, as well as their thermal stability. Ice nuclei from the bacteria P. syringae raised C. ferrugineus supercooling point from -17 to -6 degrees C, and increased mortality at -9 degrees C for 24 h from 11 to 100%. Pseudomonas syringae held at 30 degrees C for 16 weeks showed only a slight decline in its ability to reduce C. ferrugineus cold-tolerance. The fungus F. avenaceum raised the supercooling point of C. ferrugineus from -17 to -9 degrees C, but only increased the mortality at -9 degrees C for 24 h from 10 to 33%. Wheat treated with F. avenaceum and held at 30 degrees C for 4 weeks reduced the cold-hardiness of C. ferrugineus, but had no effect after 8 weeks at 30 degrees C. One reason for the difference between the two nucleators is that P. syringae had approximately 1000 times more ice nuclei per gram than did F. avenaceum. These results suggest that P. syringae is stable enough to reduce C. ferrugineus cold-tolerance after several weeks on warm grain. We discuss possible ways to increase the ice-nucleating activity of F. avenaceum.