Rapid cold hardening capacity in five species of coleopteran pests of stored grain

The capacity for rapid cold hardening was examined in recently-eclosed adults of five coleopteran species associated with stored grain, Supercooling points indicated that mortality was predominantly due to chilling injury. Threshold temperatures for indirect chilling injury for each of these species were determined by fitting survivorship data for unacclimated insects held for 0-6 h at various sub-0 degrees C temperatures to a response surface. These response surfaces were used to predict a threshold temperature for each species at which 50% of the unacclimated individuals would survive for 2 h. The survival time at this threshold temperature with acclimation for 2 h at 4 degrees C was compared to that without acclimation. The ratio of the 50% survivorship time of unacclimated to that of acclimated beetles was 8.7 for C. ferrugineus. This exceeded by over two-fold the range of 2.6-4.0 observed for the remaining species indicating that, in addition to greater innate cold hardiness, C. ferrugineus also has a greater capacity for rapid cold hardening than the other species examined. (C) 1998 Elsevier Science Ltd. All rights reserved.