Silk properties and overwinter survival in gregarious butterfly larvae

All organisms are challenged by encounters with parasites, which strongly select for efficient escape strategies in the host. The threat is especially high for gregarious species entering immobile periods, such as diapause. Larvae of the Glanville fritillary butterfly, Melitaea cinxia, spend the winter in diapause in groups of conspecifics each sheltered in a silk-nest. Despite intensive monitoring of the population, we have little understanding of the ecological factors influencing larval survival over the winter in the field. We tested whether qualitative and quantitative properties of the silk-nest contribute to larval survival over diapause. We used comparative proteomics, metabarcoding analyses, microscopic imaging, and in-vitro experiments to compare protein composition of the silk, community composition of the silk-associated microbiota, and silk density from both wild-collected and laboratory-reared families, which survived or died in the field. Although most traits assessed var...