Host plant choice, habitat selection, dispersal ability and population structure of a threatened butterfly, Lopinga achine

• Host plant choice, habitat selection and dispersal ability of the red-listed butterfly Lopinga achine were studied in partly open woodland in the province of Östergötland. Females preferred to oviposit near Carex montana, although they did not attach their eggs to any plant. Carex montana was also generally preferred by the larvae in laboratory experiments among plant species available in the field. Most of the larvae found in the field (>80%), were found on C. montana. Hence, C. montana seems to be a keystone resource for the studied populations of L. achine.Egg-laying females and larvae were found be restricted to a narrow zone along the edges of glades under a tree and bush canopy even though C. montana occurs outside this zone. This restriction to edges may be ascribed to two factors: First, egg survival was much higher at forest edges, being 48% compared with 12 and 14% in the sun of the open glades and in the shade, respectively. Second, host plant abundance in the shade under the tree and bush canopy is highest near the edge of the glades. Management to maintain glades and suitable edges is probably necessary for the long-term conservation of L. achine.Because of the recent fragmentation of its habitat, the dispersal ability of L. achine was considered important for its long-term survival. Of the 4546 individuals marked during three years, 1387 were recaptured at least once. Only 56 individuals (4,0% of the recaptured ones) were shown to have moved between populations. The mean distance between successive recaptures of the females varied between 94 and 116 meters and that of the males between 45 and 54 meters under the three years of study, and the maximum distance between any points of capture/recapture for an individual was 670 meters for one male. Movements of marked specimens between sites indicated that woods or forest edges enhance dispersal. Fewer butterflies moved between sites over open field than through woods or along edges. More females than males moved between sites and this difference increased with increasing age from three days until about ten days. Approximately 13% of the females 7-8 days old were shown to move to a new population. At this age, they had approximately 25 eggs left to lay, 15 - 20% of their total egg production. The mark -recapture results suggests that to maintain exchange between patches of L. achine they should not be farther apart than 300-800 metres depending of the matrix between patches.This study has identified the host plant, clarified habitat requirements and it has quantified movements of L. achine in Östergötland, the first necessary steps for a successful long -term conservation strategy of L. achine.

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