Effects of duration and type of cold acclimation on the subsequent cold tolerance of a tenebrionid beetle

The effects of cold acclimation on the subsequent survival and recovery of cold-exposed adults of Alphitobius diaperinus (Coleoptera: Tenebrionidae) was examined. Acclimation conditions were: 1, 2, 4 and 8 days at 5, 10, 15, 25 °C and fluctuating temperatures of 5–10-15 °C (8:8:8 h). Acute and chronic cold stresses were induced by keeping beetles at −8 °C for 8 h and 0 °C for 2, 3, 4, 5 and 6 days respectively. Survival was recorded after 5 days of recovery at 25 °C. The insects acclimated to 5, 10, 15 and 25 °C for 1 and 4 days were selected for metabolic response studies which was performed by gas chromatography-mass spectrophotometry (GC-MS). Beetles acclimated at 25 °C (control) and beetles acclimated at 5 °C for 1 or 8 days did not survive after acute cold stress. Survival increased to 100 % after acute cold stress in beetles acclimated to fluctuating temperatures for 2 days. The lethal times for 50 % of the population (Lt₅₀) were calculated for beetles after chronic cold stress and range from 4.89 days in beetles acclimated to fluctuating temperatures for 4 days–0.018 days in beetles acclimated to 5 °C for 8 days. The metabolic profile analysis showed that proline exhibited the highest concentration in all experimental groups. Increases of alanine and glycine in cold acclimated beetles were observed. Glutamic acid had opposite pattern and decreased significantly in acclimated beetles at 5 °C for 4 days. Alanine accumulation and glutamic acid decrease suggest that alanine has derived from transamination of glutamic acid and pyruvate. Erythritol, sorbitol, arabitol, adonitol, xylitol, glucose and maltose were the polyols and sugars that have been accumulated in cold acclimated beetles especially at 5 °C. Mannose has only accumulated in 1d acclimated beetles.