Effects of developmental stage, cold acclimation and diet on the cold tolerance of three species of Cryptolestes (Coleoptera: Laemophloeidae)
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Date
2020-08-26
Authors
Ganesan, Lavanya
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Abstract
Flat grain beetles (Coleoptera: Laemophloeidae) are common stored-product insect pests in Canada, infesting cereals in grain bins and equipment and end products in flour mills. This thesis reports a comparative study on the cold tolerance of three species of Cryptolestes: Cryptolestes ferrugineus, Cryptolestes turcicus and Cryptolestes pusillus.
The cold tolerance of different life stages (egg, young larva, old larva, pupa and adult) of the three species reared on flour mixed with brewer’s yeast was measured by holding insects at –(U+2212) 10oC for different durations. Probit analysis was performed to estimate the lethal time to 50 and 95% (U+0025) mortality. This was done with non-acclimated individuals (only held at 30oC) or cold-acclimated individuals (held at 18, 10 and 5oC, for 1 week/temperature). In general, the adults were the most cold-hardy stage for each of the species. Acclimated insects were anywhere from 1 (no cold-acclimation) to 14-fold more cold-tolerant than the corresponding unacclimated stage and species. Cryptolestes ferrugineus was most cold-tolerant species (requiring 58 d to reach 95% (U+0025) mortality, acclimated adult), C. turcicus was the next most cold-tolerant (39 d to reach 95% (U+0025) mortality) and C. pusillus was the least cold-tolerant (11 d to reach 95% (U+0025) mortality).
The cold tolerance of adults reared on three diets was measured both for acclimated and non-acclimated insects. In general, the adults reared on grain diet (whole wheat kernels, cracked wheat kernels and wheat germ (90:5:5 proportions) were the most cold-tolerant, adults reared on white-wheat flour and brewer’s yeast diet (95:5 proportions) had the next highest cold tolerance followed by the adults reared on 100% (U+0025) white-wheat flour. Supercooling point (SCP) of insects ranged from −(U+2212) 20.6 to −(U+2212) 26.7oC. In general, acclimated insects had slightly lower SCP than non-acclimated insects.
Possible management strategies using cold temperatures, a comparison to previous studies on Cryptolestes and cold tolerance of other species are discussed.
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Keywords
Flat grain beetles, Cold tolerance, Supercooling point, Acclimation, Temperature control, Cold shock