Substantial urbanization-driven declines of larval and adult moths in a subtropical environment

Abstract

Recent work has shown the decline of insect abundance, diversity, and biomass, with potential implications for ecosystem services. These declines are especially pronounced in regions with high human activity, and urbanization is emerging as a significant contributing factor. However, the scale of these declines and the traits that determine variation in species-specific responses remain less well understood, especially in subtropical and tropical regions, where insect diversity is high and urban footprints are rapidly expanding. Here, we surveyed moths across an entire year in protected forested sites across an urbanization gradient to test how caterpillar and adult life stages of subtropical moths (Lepidoptera) are impacted by urbanization. Specifically, we assess how urban development affects the total abundance of caterpillars and adult moths, and quantify how richness and phylogenetic diversity of macro-moths are impacted by urban development. Additionally, we determine the effects of urban warming on species-specific adult macro-moth abundance while accounting for urban development and explore how life-history traits condition species responses to urban stressors. At the community level, we find that urban development decreases caterpillar biomass and adult moth abundance. We also find sharp declines of adults in response to urban development across the moth phylogeny, leading to a decrease in species richness and phylogenetic diversity in more urban sites. Finally, our study found that smaller macro-moths are less impacted by urban development than larger macro- moths in subtropical environments, perhaps highlighting the tradeoffs of metabolic costs of urban heat island effects favoring smaller moths over the relative benefits of dispersal for larger moths. In summary, our research underscores the far-reaching consequences of urbanization on moths and provides compelling evidence that urban forests alone may not be sufficient to safeguard biodiversity in cities.