SURVIVAL OF RHYZOPERTHA-DOMINICA (COLEOPTERA, BOSTRICHIDAE) IN STORED WHEAT UNDER FALL AND WINTER TEMPERATURE CONDITIONS

Cold temperature survivorship of Rhyzopertha dominica (F.) populations with a natural age structure in stored wheat was estimated for a natural fall cooling rate of 2-degrees-C per week and winter temperatures of 17, 13, 9, and 5-degrees-C. Logistic equations were fitted to the data to predict the survivorships of the adults outside kernels and immatures and preemergent adults inside kernels as a function of exposure time over the 5-17-degrees-C temperature range. During the acclimation period, many insects died, and roughly 80,55, and 25% of the insects were alive after temperatures had decreased at a rate of 2-degrees-C per week from 17-degrees-C to 13, 9, and 5-degrees-C, respectively. At the end of cold temperature exposure period, many R. dominica survived at 17-degrees-C, a few at 13-degrees-C, but none at 5 or 9-degrees-C. The colder the temperature the more rapidly survivorship decreased. The mostly immature insect population inside kernels was killed less rapidly than the external adult population at 5 and 9-degrees-C and more rapidly at 13 and 17-degrees-C. Daily survival rates decreased and then increased again indicating that those insects surviving short exposures to cold temperatures had a greater chance of surviving long exposures to cold temperatures. These equations will help extend our population model to predict the survival of R. dominica populations in stored wheat through the winter.