Abstract
Tree-killing bark beetles and their fungal associates represent a huge economic and ecological problem in boreal forests. Tree colonization by the beetle-fungus complex is controlled by tree resistance, including induced responses programmed by prior prim ing stimuli, and tree resistance is a key regulator of bark beetle populations and their ability to reach critical threshold population densities. Our proposed research will study the molecular interaction between the induced tree defences and the beetle- fungus colonization process, and contribute to reducing impacts of these important forest pests. Keys to the beetle's success are their mutualistic relationship with phytopathogenic fungi and the ability of the beetle-fungus complex to engage in coordinat ed mass-attacks that overwhelm the defensive capacity of healthy trees. Beetle aggregation is coordinated by pheromones derived from host precursors or produced de novo by the beetles from metabolic precursors. Recent research by our group has suggested t hat priming of tree defences by application of methyl jasmonate directly interferes with beetle pheromone production and limits host colonization. This in itself is interesting because it creates opportunities to control bark beetle aggregation through ma nipulation of host tree resistance or by identifying or enhancing the pheromone modification pathway. Our proposal describes a research plan to investigate the tripartite nature of the tree colonization process at the biochemical and transcriptional level , particularly when conifer defences are primed. We will use next generation sequencing of the beetle, the fungus and the host tree transcriptome, together with quantification of tree secondary metabolites and beetle pheromones by GC-MS, to generate a mol ecular ecological portrait of the pheromone interference by the tree, and to probe for the concurrent role of the fungus in the mutualistic co-colonization process by the tree-killing bark beetle-fungus complex.
Norway