Habitat requirements and ecological drivers of the chequered blue butterfly (Scolitantides orion)

Sammanfattning

Butterfly populations are declining worldwide due to habitat loss, pollution, and climate change, highlighting the importance of maintaining suitable habitat conditions. This study investigated the status of the endangered chequered blue butterfly (Scolitantides orion) in Krokstrand, the last remaining population on Sweden’s west coast, and identified habitat requirements and ecological factors influencing reproduction and survival, to inform conservation management. The study assessed whether the population can sustain limited removal for captive breeding and whether habitat characteristics predict egg occurrence among sites and female oviposition preferences at a fine spatial scale. It further examined whether factors associated with egg presence also predict larval presence, evaluated the role of ants in larval occurrence, and assessed whether high butterfly abundance negatively affects host plants. Field surveys were conducted at ten sites in the Krokstrand area. Habitat structure, nectar resources, and host plant abundance were recorded at the site level, while egg and larval presence and abundance, plant traits, and microhabitat characteristics were recorded at the individual plant level. A total of 787 eggs were found on 288 of 8,386 surveyed host plants. No site-level habitat variables consistently predicted egg abundance. In contrast, females preferentially oviposited on taller host plants in full sun and in areas with extensive exposed rock, and larvae were more frequent in similarly open, rocky microhabitats. Larval abundance was strongly associated with ant attendance: ants were present on 77% of plants hosting larvae, and larval numbers were higher on ant-attended plants. Although egg bearing plants showed some damage, oviposition did not suppress host plant flowering at the site level.These results indicate that fine-scale thermal conditions and microhabitat quality are key drivers of reproductive success and early survival in the chequered blue butterfly, highlighting the need to prioritise management actions, such as tree removal, that enhance favourable microclimates, particularly warm, open habitats.