There is much evidence that herbivory is a key innovation for the tremendous success of insect. In this thesis I have investigated different aspects of host plant utilization and phenotypic plasticity using the polyphagous comma butterfly, Polygonia c-album. Even though external conditions affect a phenotypic plastic response, the outcome is often influenced by a genetic background which may differ among populations. In Paper I we suspected the genetic background to seasonal polymorphism to be X-linked. However, results from interspecific hybridization between two populations suggested that diapause response is instead inherited in a mainly autosomally additive fashion, with a possible influence of sexual antagonism on males. In Paper II we showed that female oviposition preference is not a plastic response influenced by larval experience, but has a genetic background coupled to host plant suitability. Further, there is a strong individual correlation between larval host plant acceptance and female host plant specificity (Paper III). We believe this to be a larval feed-back genetically linked to female host specificity: offspring to ‘choosy’ specialist mothers benefit by remaining on the original host while offspring to less discriminating generalist mothers should risk inspecting the surroundings, thus compensating for potential poor female choice. In the larval mid-gut, genes are differentially expressed depending on host plant diet (Paper IV). Therefore, we expected to find fitness consequences of host plant switch. However, although growth rate was affected in a few treatments, larvae were generally surprisingly good at adjusting to new diets (Paper V). To conclude, host plant choice in both female and larval life stage is connected to performance. Combined with increased understanding about the plastic response to diet intake and seasonal polymorphism we have gained further insights into the processes of local adaptations and speciation in the Lepidoptera. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted Manuscript; Paper 5: Manuscript

The native plant communities of Canterbury, South Island, New Zealand have been severely modified and degraded and the Canterbury Plain (750,000 ha) retains few remnants of its original forest and other ecosystems. The research presented here considers the mutualistic roles of exotic and indigenous species in the process of restoring degraded landscapes. Exotic species may have an important role in the (re) establishment of desired indigenous species, and may influence succession through to a forest dominated by them. One aspect of this work describes indigenous plant community regeneration facilitated by exotic willow (Salix spp.) woodland on the Canterbury Plain. Natural colonisation of the willow woodland by native plants was investigated, with respect to variation in the physical environment in the willow stand. Key factors in the success of willow woodland as a nursery for regeneration of native vegetation include: distance to the nearest seed source, the ability to attract seed dispersers (recruitment only occurred under perch sites), flooding potential (higher recruitment in areas less likely to flood) and possibly light availability. Control of vertebrate (and invertebrate) herbivory is also necessary for successful restoration. A second aspect was a field experiment in open pasture and in a non-native remnant woodland which was then used to investigate the effects of shelter, plant spacing, mulching and fertiliser on growth and survival of planted native woody species. With minimal management, the selected mid-late successional plants established poorly in the open pasture and had low survival rates (e.g.,Dacrycarpus dacrydioides, Pseudopanax arboreus, Aristotelia serrata, Melicytus ramiflorus). Only narrow-leaved species (e.g., Plagianthus reg ius, Hoheria angustifolia, Hebe salicifolia, Cordyline australis) survived this open pasture planting. In contrast, most species (broad and narrow-leaved) established under the sheltered sites. Exotic nursery vegetation and the establishment of native species, which will, in time, act as a seed source, will be important in successfully restoring a sustainable indigenous element in the cultural landscape of Canterbury. Ecological restoration requires an integrated approach, identifying and understanding the component processes of regeneration, and of the particular aspects/characteristics of the sites involved. This research shows that naturally established plants where existing shelter is available (in this case established willows) tend to have higher growth rates than individually planted plants in open situations, and that the availability of a suitable seed source can also contribute to successful establishment and growth rates. The meeting of restoration targets on the Canterbury Plain may be accelerated, and costs reduced, through the utilisation of areas where exotic species occur (for instance, extensive willow stands in riparian areas adjacent to waterways) and more particularly, where a local seed source is also available. The findings of this research can contribute to restoration management in helping identify the best practices, based on research, that can lead to the restoration of original plant and animal communities.