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The influence of pupal color on diapause and post-diapause success in the swallowtail butterfly Papilio machaon

Roberts, Kevin123; Lehmann, Philipp12

Published May 21, 2026 on Dryad. https://doi.org/10.5061/dryad.0gb5mkmgp

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Abstract

Color 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 color morph not expected for that generation, suggesting that pupal color 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 color morphs in diapausing pupae of the butterfly Papilio machaon. We measured metabolic rate-temperature relationships during diapause and post-diapause development under full-spectrum lights to see if brown absorb more thermal radiation. Additionally, we measured eclosion success as a function of color 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 may be associated with lower diapause metabolic rates, which may confer an adaptive advantage in the form of higher probability of successful spring eclosion. Although this study cannot mechanistically link pupal color to winter performance, it suggests color has fitness-relevance during winter and warrants further investigation.