(1) The parasitoid Aphidius colemani was reared at 15 or 25°C to induce variation in size and fat reserves; SCP and cold-tolerance were compared. Insects from both temperatures were also exposed to constant or fluctuating cold-exposure. (2) The lower SCP in mummies reared at 25°C may be partially explained by their smaller size, a negative relationship being observed between SCP and size. (3) A bimodality was observed in SCP distributions, with two modes around −26 and −22°C, likely because of presence/absence of gut content. (4) The type of exposure had a striking impact, mortality being considerably lower under fluctuating regime. (5) While energy storage is an important factor, vulnerability to chill-injury is supposed to be the primary factor regulating survival at low temperature.