The southern pine beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Curculionidae), is a prime example of a bark beetle of high ecological and economical importance. As these bark beetles adapt to a changing environment, forest managers must continue to evolve management strategies to improve forest resilience to these pests. Herein, we examined the validity of phenological trap timing cues for the annual spring D. frontalis risk assessment survey and found the traditional use of flowering dogwood (Cornus florida) (Cornaceae) bloom occurred an average of 3 weeks after peak D. frontalis spring flight activity. We also examined the natal host influence on adult beetle host selection to explore a possible explanation for the lower occurrence of D. frontalis infestations in longleaf (Pinus palustris) vs. loblolly pine (Pinus taeda) (both Pineaceae). The laboratory choice tests performed showed no selection preference based on natal host.

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

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