The influence of pupal colour on diapause and post‐diapause success in the swallowtail butterfly Papilo machaon

Colour variation of lepidopteran pupae commonly involves green and brown phenotypes, with green being more common in direct‐developing generations, and brown predominating in diapausing generations. Most research on these phenotypes has focused on benefits in predation avoidance, where green pupae are better camouflaged during summer and brown pupae during winter. Interestingly, in some butterflies, a large proportion of individuals can show the colour morph not expected for that generation, suggesting that pupal colour may have benefits beyond crypsis. Little work has focused on the differences that occur during diapause and post‐diapause development. We investigated metabolic differences and potential thermoregulatory effects between brown and green colour morphs in diapausing pupae of the butterfly Papilo machaon . We measured metabolic rate‐temperature relationships during diapause and post‐diapause development under full‐spectrum light to see if brown absorb more thermal radiation. Additionally, we measured eclosion success as a function of colour and metabolic rate. Brown pupae showed no thermoregulatory benefits in developmental time under light exposure. However, during diapause, they had lower metabolic rates across temperatures compared to green pupae. Eclosion success and timing did not differ between morphs, but individuals with high diapause metabolic rates had a low probability of successful eclosion. These findings suggest that the higher prevalence of brown pupae in the diapausing generation maybe associated with lower diapause metabolic rates, which may confer an adaptive advantage in the form of a higher probability of successful spring eclosion. Although this study cannot mechanistically link pupal colour to winter performance, it suggests colour has fitness relevance during winter and warrants further investigation.