The importance of fluctuating thermal regimes for repairing chill injuries in the tropical beetle Alphitobius diaperinus (Coleoptera: Tenebrionidae) during exposure to low temperature

In this study, the impact of acclimation (1 month at 15 degreesC vs. breeding at 30 degreesC) and fluctuating thermal regimes (daily transfers from low temperatures to various higher temperatures for 2 h) on the cold tolerance of the tropical beetle, Alphitobius diaperinus Panzer (Coleoptera: Tenebrionidae) was examined. Acclimation increased significantly the duration of survival (Lt(50)) at a constant 5 degreesC (7.7 +/- 0.3 days to 9.7 +/- 0.5 days). Survival of acclimated and nonacclimated beetles increased slightly at alternating temperatures of 5 degreesC/10 degreesC or 5 degreesC/15 degreesC. When daily transfer to 20 degreesC was applied, survival (Lt(50)) was improved markedly (nonacclimated: 15.5 +/- 0.7 days, acclimated: 19.6 +/- 0.6 days). The higher temperatures may allow progressive repair of injuries, and the effects of chilling may be repaired completely at 25 and 30 degreesC, a phenomenon recorded here for the first time. It is estimated that the theoretical upper threshold of chill injury (Th) of nonacclimated beetles is 15.1 degreesC whereas it is shifted down to 11.2 degreesC in acclimated beetles, which might enable this temperature to allow effective repair of injury.