Relationship between rapid cold-hardening and cold acclimation in the eggs of the yellow-spotted longicorn beetle, Psacothea hilaris

Rapid cold-hardening (RCH) and cold acclimation (ACC) were examined in eggs of the yellow-spotted longicorn beetle, Psacothea hilaris (Pascoe) (Coleoptera: Cerambycidae). When eggs incubated at 25 °C were transferred directly to conditions of −22 °C for 2 h, less than 30% survived, whereas exposure to 0 °C for 4 h prior to transfer to −22 °C increased survival to nearly 60%. The rapidly enhanced cold tolerance (RCH) was transient and lost rapidly after 1 h at 25 °C. Incubation at 15.5 °C for 9 days (ACC) also enhanced cold tolerance. Comparison of the cold tolerance of non-treated eggs and eggs pre-treated to give RCH, ACC, or ACC+RCH allowed the relationship between the two hardening processes to be determined. At a mild subzero temperature (−10 °C) an RCH effect was not detected, whereas only RCH is effective at the severest subzero temperature just above the SCP (−26 °C). At intermediate temperatures (−16, −22 and −25 °C), ACC and RCH enhanced survival in combination. Therefore, the two hardening processes have different physiological bases but operate concomitantly over a wide temperature range.