Recipient Organization
UNIVERSITY OF MONTANA
COLLEGE OF FORESTRY AND CONSERVATION
MISSOULA,MT 59812
Performing Department
College of Forestry and Conservation
Non Technical Summary
Bark beetles are associated with fungi that support their success in colonizing trees. While many of these fungi are known to provide nutritional benefits to the beetle, other effects have also been hypothesized, particularly a role in tree killing. Despite years of speculation as to what roles fungi may play in killing trees no definitive experiments have been performed to determine the validity of this hypothesis nor the physiological effects their growth have on trees. This project will test for the ability to remove fungi from the system to develop appropriate controls and develop preliminary data looking at the putative roles of these fungi in tree-killing by bark beetle associated fungi. This will be done through a series of fungicide injections into trees that will then be inoculated with fungi or baited with pheromones to initiate bark beetle attacks. The fungi, beetles, and physiology of the trees will be tracked for two years in treated and control trees.
Animal Health Component
(N/A)
Research Effort Categories
Basic
(N/A)
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
We are conducting a comprehensive and transformative experimental study to examine the putative mutualism between bark beetles and fungi. Using a factorial experimental design we are investigating changes in tree function during and after bark beetle attacks and fungal inoculation to determine the respective roles of fungi and beetles in tree mortality which is required for fungal and beetle success. We are using three different host species-beetle-fungal systems to examine the impact of differing host defense strategies (preformed versus inducible) on the strength of the putative beetle-fungal mutualism. We are testing three hypotheses about the dependence of bark beetles on fungi. This research will increase our understanding of other tripartite symbioses involving plants, insects, and microbes by elucidating the role of host defense strategy in mutualisms.
Project Methods
We are using use three bark beetle/fungi/host pine tree systems, two of which have hosts with strong induced resin defense against bark beetles and one that has a host with weak induced defense but strong constitutive defenses. In Montana our system will be the mountain pine beetle (Dendroctonus ponderosae), a species known for region level outbreaks, and lodgepole pine (Pinus contorta Doubl. Ex Loud.), a tree species know to have strong inducible defenses . Mountain pine beetle, and its fungal associates, have been relatively well studied in this system. The Louisiana system, consists of loblolly pine (Pinus taeda L), another tree with a strong inducible defense and southern pine beetle (Dendroctonus frontalis) another aggressive tree-killing bark beetle species. The beetle and its fungal associates have been extensively studied in this system. The Arizona system has not been studied as extensively. Ponderosa pine (Pinus ponderosa Dougl. Ex Laws) in this system is attacked by several species of beetles which are generally found occurring in the same tree, often with little observable niche separation . Dendroctonus species occurring at this site include southern pine beetle (D. frontalis), western pine beetle (D. brevicomis LeConte), roundheaded pine beetle (D. adjunctus Blandford) and larger Mexican pine beetle (D. approximatus Hopkins) . Unlike the other two systems, Dendroctonus in Arizona have historically had very few landscape-level outbreaks. In addition, contrary to our other proposed study systems, ponderosa pine in Arizona have been shown to have little inducible defense. The use of three study systems with different outbreak histories, different bark beetle species, different suites of fungi, and different host defense strategies will allow us to evaluate the complexity of the putative bark beetle/fungal mutualism over conifer forests that occur over vast areas of North America. Defense depletion hypothesis: Support for the defense depletion hypothesis will be provided by an equal rate of depletion in resin exudation (amount/time) and equal rate of change in resin quality (terpenes) and size and speed of necrotic lesion formation indicating that the fungus alone is responsible for these changes. Evidence against the defense depletion will be provided by a faster depletion of defenses and/or beetles successfully establishing in the phloem (and that these broods successfully emerge as adults) prior to the activation of inducible defenses. Water transport disruption hypothesis: Support for this hypothesis will be supplied by a finding of a rapid reduction in tree water potential and sapflow prior to beetle establishment. Evidence that beetles establish and are successfully reproducing prior to water disruption will be regarded as evidence against this hypothesis. Host defense regulation of defense depletion; Support for this hypothesis will be provided by greater depletion of host defense by fungi, in the two host systems with strong induced defense (loblolly pine, lodgepole pine) compared with the system with weak induced defense (ponderosa pine).