Host-plant specialisation and habitat restrictions in an endangered insect, Lycaena dispar batavus I. Larval feeding and oviposition preferences

The Large Copper butterfly, Lycaena dispar, is extinct in Britain and rapidly declining in the rest of Europe, due predominantly to loss of its wetland habitats. In the Netherlands the Sub-species L. d. batavus is at the edge of its range in Northern Europe and, as with most marginal butterflies, has more specialised food plant and habitat requirements than the core Populations of L. d. rutilus. We investigate reasons for the relative specialisation of L. d. batavus on Rumex hydrolapathum in a fenland habitat when compared to the more widespread and common L. d. rutilus. Host-plant choice by ovipositing females and by larvae are measured as well as larval performance oil alternative hosts. Laboratory experiments reveal that larvae are able to feed oil other Rumex species without detriment to their overall survival and Call Utilise these alternative host plants at least as efficiently as their natural host plant. This Suggests that plant chemistry is not responsible for their lack Of utilisation in the wild. Under greenhouse conditions, females showed all equal willingness to oviposit oil host and alternative Rumex, expressing no significant preference for ally particular plant species. However, in field experiments using free-ranging females in a fenland habitat, eggs were laid only on R. hydrolapathum. Our interpretation is that there are no short distance cues discriminating between the three Rumex species but longer distance cues in the field Situation may operate to maintain this host-plant specialisation. The selection pressure maintaining L. cl. batavus as a specialist oil R. hydrolapathum in a wetland may underlie its Current rarity.