My research group have focussed on invasion biology of two major forest pests: (A) mountain pine beetle (MPB), and (B) Septoria canker caused by Sphaerulina musiva. While we have been working on the former since 2007, the latter is a relatively new research topic in my research group.
(A) We have investigated the jack pine suitability as a host for the invasive MPB. As a result, we have identified four likely mechanisms that have facilitated the host range expansion of MPB into the jack pine forests. (1) Jack pine trees appeared to have lower chemical defenses than a historical host of MPB, lodgepole pine (Pinus contorta). In particularly, jack pines not only quantitatively lack important defense chemicals (e.g. limonene), but also contains large amounts of chemicals (α-pinene) that can facilitate beetle colonization of host trees. These mechanisms have helped beetles to overcome jack pine defenses. (2) prior to its expansion into jack pine forests, MPB invaded a zone of jack-lodgepole pine hybrids in Alberta. This has facilitated host shift and improved beetle success on jack pine because hybrids show chemical characteristics of both jack and lodgepole pines. (3) similarities in the composition of monoterpenes between jack and lodgepole pines have allowed MPB to colonize jack pine as its chemicals are compatible for pheromone production, aggregation on host trees, and larval development. (4) Jack pine is suitable for the growth of fungal and bacterial symbionts of MPB as these symbionts are vital for detoxifying toxic defense chemicals and providing nutrients for larvae.
We are currently: (a) determining if gradients of soil nutrients and water affect chemical defenses in jack pine and thus its susceptibility to MPB, (b) investigating the effects of host nutrients on MPB-symbiotic fungal interactions, (c) examining the effects of beetle-associated fungi on interactions between two competing bark beetle species, MPB and Ips pini on jack pine, (d) investigating the effects of host tree nutrients on development of MPB larvae, (e) developing monitoring tools to detect MPB at low densities on the eastern and northern edge of beetle expansion into Saskatchewan and NW Territories, and (f) characterizing growth-defense relationship of lodgepole pine trees survived from MPB outbreaks relative to the beetle-killed trees.
(B) Regarding Sphaerulina musiva, the causal agent of stem canker in poplars, we have investigated if an increase in susceptibility of Populus balsamifera observed from eastern to western Canada is driven by a potential increase in introgression of the highly susceptible species Populus trichocarpa into P. balsamifera populations. We selected 200 genotypes from P. trichocarpa and P. balsamifera and their hybrids, after sequencing and analyzing them with SNP to determine their level of species purity and introgression. Selected genotypes were infected with a mix of S. musiva isolates (Alberta, Ontario, and Quebec) in a greenhouse trial. Based on the SNP panel used, several putative balsam poplars in Alberta were deemed hybrids with different levels of P. trichocarpa. In addition, we found a strong correlation between the proportion of P. trichocarpa in the genome and the severity of the disease in P. balsamifera. Furthermore, metabolite profiling revealed several chemicals involved in the response with the potential to be used as tracers for susceptibility.
The recent eastward expansion of MPB into lodgepole pine forest ecosystems that lack a co-evolutionary history with MPB in western Alberta has created a cascading impact on the above ground plant community and below ground soil fungal community. Apparently, changes in soil chemistry, particularly reduction in phenol and increase in nitrate concentrations, through increased litter inputs may have driven the shift in the microbial communities observed. We further show that these changes have ecological consequences on the new generation of pine seedlings above ground as seedlings grown with beneficial (ectomycorrhizal) fungi collected from beetle-killed stands had reduced abundance of defense compounds, relative to seedlings grown with fungi collected from healthy stands. Plants with lower defenses are more vulnerable to insect and disease attacks.
We are currently: (a) evaluating the association between pine seedling quality and ectomycorrhizal fungal community type (single vs multiple fungi), (b) characterizing how soil fungal communities (ectomycorrhizal, saprophytic, and pathogenic) are affected by an array of individual and cumulative forest disturbances (fire, harvesting, and insect outbreak), (c) identifying the components of fungal communities that promote successful lodgepole pine regeneration, (d) testing if soil fungal communities can be amended to improve post-disturbance regeneration, and (e) identifying if changes in soil microbial community and organic volatile emission in response to disturbances.
We have currently two projects that focus on plant-tree-pathogen interactions. In one project, we investigate ecology and phenology of a resident Aphelinid wasp (Coccophagus sp.) and evaluation of its potential as a biocontrol agent of European elm scale (Eriococcus spurius). In the second project, we investigate the role of the chemical responses of aspen to competition and herbivory.