Effects of developmental stage, cold acclimation and diet on the cold tolerance of three species of Cryptolestes (Coleoptera: Laemophloeidae)

Flat grain beetles (Coleoptera: Laemophloeidae) are one of the more cold-tolerant and common stored-product insects in Canada. Cold tolerance was measured for different life stages (egg, young larva, old larva, pupa and adult) of the three species reared on flour and brewer’s yeast. This was done with non-acclimated (only held at 30^oC) or cold-acclimated individuals (held at 18, 10 and 5^oC, for 1 week/temperature). Cold tolerance was measured by survival at −10^oC for different durations. Adults were the most cold-hardy life stage for each of the species. Acclimation increased the cold-tolerance by up to 14-fold compared to the corresponding unacclimated stage and species. Some stages and species did not increase their cold tolerance with acclimation. For acclimated adults, Cryptolestes ferrugineus was most the cold-tolerant species (LT₉₅ = 58 d, Lethal Time for 95% of the population), followed by C. turcicus (LT₉₅ = 39 d) and C. pusillus was the least cold-tolerant (LT₉₅ = 11 d).
The effect of diet on cold tolerance was tested using three different diets. Adults reared on grain diet (whole wheat kernels, cracked wheat kernels and wheat germ, 90:5:5 proportions) were the most cold-tolerant, followed by adults reared on white-wheat flour and brewer’s yeast diet (95:5 proportions) and adults reared on 100% white-wheat flour had the least cold-tolerance.