Biology and habitat requirements of the highly endangered butterfly Tomares nogelii (Lepidopterda, Lycaenidae) in southeastern Romania

Understanding the ecological mechanisms limiting population persistence is essential for the conservation of highly specialised and endangered insects. Tomares nogelii dobrogensis is one of the rarest butterflies in the European Union and is strictly monophagous on Astragalus ponticus in Romania. Despite its high conservation relevance, quantitative data on its ecology and life history have been largely lacking. During the 2025 flight season, an extensive field study in northern Dobrogea, Romania, investigated phenology, imaginal lifespan, behaviour, habitat characteristics and host-plant synchrony across six colonies. Patch-level analyses were used to assess how habitat structure, light availability and host-plant phenology influenced imaginal abundance. Oviposition patterns and preimaginal stages were documented. Imaginal flight activity closely overlapped with the reproductive phenology of A. ponticus , with peak butterfly abundance coinciding with bud formation and flowering. Observed imaginal lifespan was short, resulting in a narrow reproductive window. At the patch scale, imago abundance increased strongly with host-plant patch area and light availability, while host-plant density alone was not a significant predictor. Oviposition was highly aggregated among host plants, occasionally leading to high larval densities and cannibalism. Implications for insect conservation Our results indicate that population performance of T. n. dobrogensis is primarily constrained by the spatial and temporal availability of suitable host-plant stages. Conservation management should therefore prioritise the maintenance of large, open A. ponticus patches and prevent disturbances by lifestock during flight time and the larval feeding period which was shown during the study to significantly reduce reproductive success.