Many insect species have evolved different overwintering survival strategies such as cold tolerance and/or diapause. This study investigated the relationship between Aphidius rhopalosiphi mummy colour and cold tolerance and diapause. Mummy colour was insufficient to discriminate diapausing from non-diapausing individuals. This phenotypic character seems to reflect environmental conditions rather than direct developmental time and cocoon thickness (identification criteria of diapause). There is, however, a relationship between cold tolerance and mummy colour. Dark mummies exhibited significantly higher water content, survival at low temperature and lower supercooling point values than pale mummies. Mummy colour in Aphidius rhopalosiphi seems to be a phenotypic indicator of the cold tolerance. Whole animal physiology; Colour and luminescence; Life cycle and development; Development; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Abiotic factors; Physical factors Aphidius rhopalosiphi (Aphidiidae); Temperature relationships; Cold tolerance; Diapause; Hemipteran hosts; Aphidoidea; Host mummy colour, indicators of parasite diapause & cold tolerance; Temperature Aphidoidea; Colour; Hymenopteran parasites; Aphidius rhopalosiphi; Host mummy colour, indicator of parasite diapause & cold tolerance none