The cold-hardiness of fourth-fifth instars of the Japanese pine sawyer, Monochamus alternatus Hope, collected from 25 to 28 April in spring, 28 June to 1 July in summer, 29 October to 1 November in autumn, and 28 December to 1 January in winter in Anhui Province, China, was compared. Parameters compared were supercooling point (SCP), lethal temperature causing 50% mortality (LT50), upper limit of cold injury zone above which temperature does not cause mortality even after an ecologically meaningful period of time (ULCIZ), sum of injurious temperature that is the duration of effective chilling that results in 50% mortality (SIT), and acclimation efficiency. The mean SCP values of summer, autumn, winter, and spring larvae were −6.2, −10.9, −15.4, and −12.3°C, respectively. The cold-hardiness of larvae collected in different seasons was consistent with seasonal air temperature in the wild. There was a significant positive correlation between SCP and LT50 (r = 0.979, P < 0.05), between SCP and monthly mean air temperature (r = 0.990, P < 0.01), and between SCP and monthly mean absolute minimum air temperature (r = 0.995, P < 0.01). ULCIZ and SIT for autumn, winter, and spring larvae were 4.9, 9.7, and 4.7°C and 1.356, 16.142, and 5.323 DD, respectively. Autumn larvae displayed significant acclimation efficiency at 5 and 0°C; however, exposure to −5°C did not enhance the cold-hardiness of larvae from any season. Cold-hardiness of M. alternatus larvae seems to increase in autumn, peak in winter, and decline in spring. Results suggest that M. alternatus drops SCP through acclimation in autumn to avoid freezing and reduces ULCIZ or increase SIT to increase its chilling tolerance at low temperature in winter.
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