Chemotypic variations of lodgepole pine affect mountain pine beetle behaviour and growth of its symbiotic fungus

• Author / Creator

  Aziz Ullah, .

• Plants generally show large chemotypic variations in susceptibility to phytophagous insects and pathogens. Plant chemical defenses, or secondary compounds, are important components of plant resistance to pest organisms. Among plants, coniferous trees produce complex oleoresins that contain toxic chemicals. Terpenes are the main components of oleoresins and mainly consist of volatile monoterpenes, semi-volatile sesquiterpenes, and non-volatile diterpene resin acids. Collectively, these terpenes play a critical complementary role in the defenses of conifers. Lodgepole pine is one of the most abundant and widespread conifer species in western North America. It shows strong constitutive and inducible defense responses to plant pathogens and herbivorous insects, particularly bark beetle species. The mountain pine beetle is one of the primary insect enemies of lodgepole pine. The mountain pine beetle is a native forest insect species in western North America, and during periodic outbreaks it can kill millions of pine trees. Yet, some individual trees survive from these high-density bark beetle attacks. Mechanisms driving the survival of these pine trees are not clear but are mostly likely related to their defense chemicals.
  In this study, we utilized the natural variation in chemical defenses of lodgepole pine trees from progeny trials in northern Alberta. These were grouped in four clusters (chemotypes) based on the composition of mainly constitutive monoterpene concentrations using cluster analysis. We selected representative pine families in each cluster (total 11) and used their profiles in laboratory bioassays. Our goal was to determine whether chemotypes of lodgepole pine differentially affect performance of mountain pine beetle and its major fungal symbiont, Grosmannia clavigera. We hypothesized that the chemotypic variations in lodgepole pine families differentially influence host acceptance by mountain pine beetle and growth of G. clavigera.
  We conducted two bioassays to assess the impact of chemotypes on the performance of mountain pine beetle and G. clavigera. For the mountain pine beetle assays, we used a diet that consisted of phloem and sapwood, mixed with agar and water. For G. clavigera, we prepared malt extract agar. In each bioassay, we either placed adult beetles or inoculated fungi on artificial diet amended with the monoterpene concentrations representing each of four pine clusters or 11 lodgepole pine families. We measured beetle egg gallery length and weight change as a proxy to host selection by beetles as well as fungal growth as a proxy to fungal responses to host chemistry. We found a significant effect of chemotypes on beetle egg gallery length and weight change. Three pine families were least suitable for beetle performance and two families were least suitable for the fungal growth. The families which showed the least suitability for beetle host acceptance had higher concentrations of limonene, γ-terpinene, 4-allylanisole, β-pinene, terpinolene, and cymene. The families with the lowest fungal growth had higher concentrations of α-pinene, 3-carene, camphene, myrcene, γ-terpinene, bornyl acetate, borneol, and total monoterpenes.
  Overall, our study is the first to demonstrate how host phytochemistry differentially affects a bark beetle species and its fungal symbiont. Furthermore, this study reveals that performance of both mountain pine beetle and G. clavigera can be affected by host chemotypes. Pine families which show low suitability for both beetles and its symbiont can be potentially used in restoration of mountain pine beetle impacted forests in Alberta to promote beetle-resistant forests.

• Subjects / Keywords

  • plant-insect interactions
  • monoterpenes
  • Grosmannia clavigera
  • host acceptance
  • beetle behaviour
  • Chemotypes
  • pine defenses
  • fungal growth
  • fungal symbiont
  • Dendroctonus ponderosae
  • Pinus contorta

• Graduation date

  Spring 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-4hcn-k961

• License

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