Asymmetry in host plant preferences of two ecotypes of Boloria eunomia (Lepidoptera: Nymphalidae)

Abstract

The diversity and evolution of host-plant relationships of butterflies has been the subject of much research. In this context, an interesting species is the bog fritillary Boloria eunomia. Across its boreo-montane distribution there are several ecotypes of this butterfly (sometimes distinguished as subspecies), which inhabit distinctly different habitats. However, little is known about the relationships between these forms in terms of host-plant use. We compared larval preferences of two ecotypes in north-eastern Poland, a unique region that is inhabited by different evolutionary lineages of B. eunomia. Larvae of the meadow ecotype reared in captivity were able to grow and develop exclusively on Persicaria bistorta, i.e., their ‘native’ host plant. In contrast, larvae originating from populations inhabiting raised bogs generally showed poorer survival, though they accepted both Ericaceae species growing in their biotope and P. bistorta, a plant that does not occur in their biotope. They did not show clear food preferences, but mortality was lowest when they were fed Vaccinium uliginosum. This is puzzling as field observations indicate that Vaccinium oxycoccus is the main host plant in the area studied. However, our findings are consistent with the results of phylogeographical studies indicating that meadows were the ancestral habitats of B. eunomia and some populations adapted later to different biotopes. The poor survival of larvae of the bog ecotype recorded in the present study may indicate that this form is at least locally potentially more vulnerable than the other ecotype.