Lycaena dispar on its northern distribution limit: an expansive generalist

The aim of this study was to evaluate host plant and habitat preferences of Lycaena dispar, an oligophagous butterfly species endangered in some parts of its European range. In laboratory trials, the females of Estonian populations accepted various species of Rumex as oviposition substrates. Growth performance of the larvae did not differ between the hosts offered (only R. acetosa proved to be unsuitable). In the field, extensive use of the two most common host species - R. crispus and R. obtusifolius - by the Estonian populations of L. dispar was confirmed. Unlike in the laboratory, larval performance in the field was better on R. obtusifolius than R. crispus. A likely explanation is the more ephemeral character of the aboveground parts of R. crispus plants: these tend to wilt before the larvae of L. dispar have reached the stage adapted to hibernation. A countrywide analysis of landscape occupancy revealed a positive association of the occurrence of L. dispar with ditches and human settlement. We conclude that moderate anthropogenic pressure maintains suitable habitats for L. dispar through creating favourable conditions for R. obtusifolius, the primary host of the butterfly in the region. Due to its generalism in both host and habitat use, L. dispar is not in the need of active conservation measures on the current northern limit of its distribution. The favourable status of the species in Estonia is corroborated by its recent range expansion which parallels similar trends elsewhere in Eastern Europe.