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A study was carried out on the overwintering of Aphidecta obliterata (L.) in north-eastern Scotland, UK. It was found that measured supercooling temperatures were lower in adults with empty guts (around -30 deg C) than in those with full guts (around -13 deg C), and were not affected by sex. Hibernating adults were able to supercool to between -8 and -18 deg C, this ability decreasing with time. No polyhydric alcohols were isolated from the insects, and the water content was not related to supercooling ability, but it decreased significantly following a period of low precipitation or isolation in the absence of free water. A decrease in fat reserves was observed in adults prior to overwintering, while they remained constant during hibernation and decreased further during the post-hibernation period. Both pre-hibernation and hibernating adults showed a decreased respiration rate in comparison with post-hibernation adults, indicating the attainment of a true state of diapause. Lack of water, low temperature and possible fungal attack appeared to be significant mortality factors.