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 g rain enough to control C. ferrugineus quickly, we have examined ways t o reduce the cold-tolerance of adult C. ferrugineus, the most cold-har dy stage. We compared the efficacy of two ice nucleators, Pseudomonas syringae and Fusarium avenaceum, to decrease cold-tolerance of this in sect, as well as their thermal stability. Ice nuclei from the bacteria P. syringae raised C. ferrugineus supercooling point from -17 to -6 d egrees 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 on ly a slight decline in its ability to reduce C. ferrugineus cold-toler ance. The fungus F. avenaceum raised the supercooling point of C. ferr ugineus 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 reas on for the difference between the two nucleators is that P. syringae h ad approximately 1000 times more ice nuclei per gram than did F. avena ceum. These results suggest that P. syringae is stable enough to reduc e C. ferrugineus cold-tolerance after several weeks on warm grain. We discuss possible ways to increase the ice-nucleating activity of F. av enaceum.