Population Traits and Threats of Phengaris arion (Lepidoptera: Lycaenidae) in Western China

The large blue butterfly, Phengaris arion, exhibits particular habitat requirements owing to its specialized myrmecophilous association with host ant species, which substantially limits its population size and persistence. To characterize the population characteristics and threatening factors of this species in western China grasslands, we conducted Mark–Release–Recapture (MRR) surveys at a single habitat patch in Qiangtan Village, located in Gansu Province, Jishishan Baoan, Dongxiang and Salar Autonomous County, from 2022 to 2024. We quantified population abundance and structure and assessed anthropogenic and climatic threats to the local population. Our results showed that the local population size of P. arion exceeded 1000 individuals (95% CI: 952–1106.07). Adults emerge in July, with flight activity peaking in mid-to-late July. The population exhibited a female-biassed sex ratio of 1.12:1, a maximum adult lifespan of 16 days, and a maximum dispersal distance of 657 m; most individuals remained within an activity radius of 500 m. The studied population is subjected to multiple stressors, including anthropogenic disturbances (e.g., artificial mowing and overgrazing) and extreme climatic events. In particular, hailstorms trigger pronounced declines in adult abundance. Our findings support that implementing targeted mowing restrictions represents a core conservation measure for sustaining local P. arion populations.