Constitutive foliar metabolite variation in conifers shapes their susceptibility to the invasive herbivore Lymantria dispar asiatica

Forest ecosystems are increasingly threatened by invasive pests due to global trade and changing environmental conditions. Improving tree resilience through selective breeding represents an effective management strategy. We used a combination of Lymantria dispar asiatica insect rearing, host metabolomic profiling, and full-sib family effect parameter evaluation of metabolites to identify defenses with greatest genetic potential. Among conifers studied for larval development, coastal Douglas-fir was the most and Norway spruce the least favorable host. Phenolics in foliage grouped conifer species phylogenetically, whereas terpenes reflected feeding behavior of the larvae better. Analysis of Douglas-fir full-sib families revealed moderate to high family effects of phytochemicals, suggesting potential for direct improvement of resistance. However, terpene profiles of nursery versus field grown Douglas-fir and Norway spruce were highly dissimilar, illustrating environmental and ontogenetic variability of biochemical traits. Insect bioassays thus need to be directly linked to terpene profiles of tested trees and data cannot be extrapolated to the species level. This integrated framework proposes a way for identifying targeted defenses and assessing their genetic potential, supporting evidence-based strategies for developing pest-resistant forest trees under increasing biological invasions. Follow-up work is needed to enhance phenotyping capacities of targeted resistance traits and obtain breeding values for these.