The large copper butterfly, Lycaena dispar batavus, a subspecies of much conservation interest, is host-specific to the great water dock, Rumex hydrolapathum, but little is known of the relationship between herbivore and host in wild populations. This study investigated the distribution of both R. hydrolapathum plants and L. d. batavus eggs in four different habitat types within the Weerribben National Park, The Netherlands, during the summer of 1993. As expected, host plant distribution strongly influenced that of its herbivore. Further, both species had significantly aggregated distributions, and that of R. hydrolapathum was in agreement with the negative binomial model. Host plant selection for oviposition showed no significant relationship with physical plant characteristics, such as plant height and the number of leaves, and at the scale studied, habitat type was of only limited influence. The possible influence of the vegetational architecture surrounding host plants is discussed.
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 on alternative hosts. Laboratory experiments reveal that larvae are able to feed on other Rumex species without detriment to their overall survival and can 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 an equal willingness to oviposit on host and alternative Rumex, expressing no significant preference for any 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. d. batavus as a specialist on R. hydrolapathum in a wetland may underlie its current rarity.