Overwintering strategy drives phenological sensitivity and mismatch with vegetation green-up for temperate butterflies

Processes regulating insect herbivore abundance are poorly understood despite their important role in food webs and recently documented declines. Seasonal trophic mismatches resulting from climate change may be particularly crucial in determining insect abundance change, but studies of plant-insect mismatch at broad spatial and temporal extents are nascent. Here we unveil an analytical framework for assessing broad scale plant-insect phenologies and their relationship to community-level abundance patterns of butterflies. Our analysis was developed to be as species neutral as possible, instead considering a key species trait, overwintering diapause stage. This approach can be used across broad spatiotemporal scales and multiple taxa, including less well studied groups. Using community science butterfly observations from multiple platforms and across the Eastern USA, we show that the relationships between environmental drivers, phenology, and abundance depend on overwintering diapause stage. In particular, egg-diapausing butterflies show marked changes in adult onset phenology in relation to plant phenology and are rapidly declining in abundance over an almost twenty year span across the region. Our results also demonstrate negative consequences of warmer winters, irrespective of plant phenology, especially for abundance of egg-diapausing butterflies. In sum, phenological sensitivity and abundance changes dramatically differ depending on diapause stage , providing a basis for predicting the winners and losers under environmental change. Utilizing a framework that ties thermal performance across life stages in relation to climate and lower trophic level phenology provides a critical step toward predicting the fate of butterflies and other herbivorous insects into the future.