Biodiversitet innebär en hög artsammansättning och är viktigt för fungerande ekosystem. Almar (Ulmus-arter) är ett träd som hyser en mängd andra arter och som värderas högt i urbana miljöer. Almar drabbas tyvärr av svampsjukdomen almsjukan som leder till att trädet dör. Detta kan dock motverkas med hjälp av vaccinet Dutch Trig®. Det är känt att vaccinet motverkar almsjukan men kunskapen om vaccinet möjligen påverkar andra arter och organismer än almsjukan är låg. Denna studie utfördes i syfte att undersöka och jämföra om epifyters mångfald och allmäntillståndet mellan ovaccinerade och vaccinerade almar skiljde sig. Metoden för studien delades upp i två delar, en tillväxtmätning och visuell granskning samt en kartläggning av epifyter. Resultatet och analysen visade att skillnaden mellan grupperna hos en variabel var signifikant, hos resterande variabler kunde skillnaderna bero på slumpen. Trots detta kunde ändå vissa mönster utläsas och slutsatsen att det fanns en skillnad både i allmäntillstånd och biodiversitet kunde dras.

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