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   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
   for bark beetles    
    When metabolizing spruce bark, the insect's fungal partners release   
   volatile compounds that bark beetles recognize through specialized olfactory   
   sensory neurons    
      
     Date:   
         February 21, 2023   
     Source:   
         Max Planck Institute for Chemical Ecology   
     Summary:   
         An international research team demonstrates that the European spruce   
         bark beetle (Ips typographus) uses volatile fungal metabolites of   
         plant defense substances as important chemical signals in their   
         attack on spruce trees. The researchers also show that the insects   
         have olfactory sensory neurons specialized for detecting these   
         volatile compounds. The fungal metabolites likely provide important   
         clues to the beetles about the presence of beneficial fungi, the   
         defense status of the trees, and the population density of their   
         conspecifics. The study highlights the importance of chemical   
         communication in maintaining symbiosis between bark beetles and   
         their fungal partners.   
      
      
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   FULL STORY   
   ==========================================================================   
   In a new study in the journal PLOS Biology, an international research   
   team led by the researchers from the Max Planck Institute for Chemical   
   Ecology demonstrates that the European spruce bark beetle Ips typographus   
   uses volatile fungal metabolites of plant defense substances as important   
   chemical signals in their attack on spruce trees. The researchers also   
   show that the insects have olfactory sensory neurons specialized for   
   detecting these volatile compounds.   
      
   The fungal metabolites likely provide important clues to the beetles   
   about the presence of beneficial fungi, the defense status of the trees,   
   and the population density of their conspecifics. The study highlights   
   the importance of chemical communication in maintaining symbiosis between   
   bark beetles and their fungal partners.   
      
      
   ==========================================================================   
   The mass outbreaks of bark beetles observed in recent years have caused   
   shocking amounts of forest damage throughout Germany. As reported by   
   the Federal Statistical Office in July 2022, more than 80% of the trees   
   that had to be felled in the previous year were damaged by insects. The   
   damaged timber felled due to insect damage amounted to more than 40   
   million cubic meters. One of the main pests is the European spruce beetle   
   Ips typographus. In the Thuringian Forest and the Harz Mountains, for   
   example, the beetle, which is only a few millimeters long, encountered   
   spruce monocultures that had already been weakened by high temperatures   
   and extended periods of drought, which facilitated the spread of the pest   
   and led to the death of huge forest stands within a short period of time.   
      
   Researchers have already known that chemical communication plays an   
   important role in bark beetle mass attacks. Beetles first choose a   
   suitable tree and then emit so-called aggregation pheromones. These   
   pheromones attract conspecifics in the vicinity to join a mass attack   
   that overcomes the tree's defenses. Spruce trees whose defenses are   
   already weakened by stresses are more readily overcome.   
      
   Bark beetles like the odor of their symbiotic fungi Spruce bark beetles   
   need fungal allies to successfully reproduce in the trees.   
      
   The fungi are ectosymbionts, symbiotic partners that live outside the   
   beetles.   
      
   Each new generation of beetles must find their symbiotic fungi and carry   
   them to a new host tree.   
      
   In a new study, an international research team led by Dineshkumar   
   Kandasamy (now at Lund University, Sweden) and Jonathan Gershenzon of   
   the Max Planck Institute for Chemical Ecology in Jena, Germany, reports   
   that the European spruce bark beetle can find its fungal partners   
   based on the volatile chemical compounds the fungi release when they   
   degrade spruce resin components. "We had already been able to show that   
   bark beetles are attracted to their fungal associates when these are   
   cultured on standard fungal growth medium. Now we wanted to know what   
   would happen if we grew fungi on a more natural medium with spruce bark   
   powder added. Would beetles be attracted to fungi now? If so, which   
   chemical compounds would be responsible for the attraction and what is   
   the origin of these chemicals?" says first author Dineshkumar Kandasamy,   
   explaining the study's initial questions.   
      
   Fungi convert the chemical defenses of spruce into attractants for the   
   beetles European spruce bark beetles are associated with fungal partners   
   of different genera. The fungus Grosmannia penicillata grew particularly   
   well on the spruce bark medium and produced more volatile compounds than   
   most of the other fungi tested. Therefore the researchers focused their   
   investigations on this fungus.   
      
   The researchers set up special experimental arenas where they could   
   test whether the beetles were attracted to volatile compounds emitted   
   by the fungi.   
      
   "We first found that European spruce bark beetles are attracted to the   
   volatiles emitted by their associated fungi when fungi were growing on   
   medium with spruce bark powder. However, we also showed that fungi can   
   transform terpene compounds from spruce resin into their oxygenated   
   derivatives and that some of these metabolites produced by fungi are   
   particularly attractive to bark beetles. The overall conclusion is   
   that these volatiles serve as chemical signals that keep the symbiosis   
   between bark beetles and their associated fungi going," says Dineshkumar   
   Kandasamy.   
      
   The researchers found that pathogenic fungi, which are harmful to the   
   beetles, can also metabolize spruce resin compounds. However, unlike the   
   metabolites of the symbiotic fungi, the resulting derivatives are not   
   attractive to bark beetles. Bark beetles can therefore use their sense   
   of smell to distinguish whether the fungi present in the tree are good   
   or bad for them. The scientists were particularly surprised when the   
   behavioral observations revealed that fungal partners not only attracted   
   the beetles but also stimulated them to tunnel.   
      
   Bark beetles have olfactory sensory cells in their antennae tuned to   
   detect volatile compounds of fungal metabolism Further evidence that   
   fungal metabolites make spruce trees already infested by fungi even   
   more attractive to bark beetles was provided by electrophysiological   
   studies of the beetles' perception of these odors. This involved testing   
   the response of individual olfactory sensilla on the beetle antennae to   
   different odors. The researchers were able to show that the bark beetles   
   possess certain olfactory sensory neurons housed in sensilla that are   
   specialized in detecting oxygenated monoterpenes emitted by the fungi.   
      
   "By enhancing bark beetle attraction to particular trees, volatiles from   
   the fungus could increase the intensity and success of mass attacks. Fungi   
   may help kill the host tree, overcome its defenses, provide beetles with   
   nutrients or protect them from pathogens. The ability of the fungus to   
   metabolize resin components that are originally produced by the tree   
   as a defense could indicate which fungi are virulent and could serve as   
   good partners for the beetle," says Jonathan Gershenzon.   
      
   The results of this new study may help improve the control of bark beetle   
   outbreaks. One of the most widely used strategy in the fight against   
   these pests are pheromone traps, but these have not been effective   
   in preventing recent outbreaks. Therefore, the researchers are now   
   testing whether these odor traps can be optimized by adding oxygenated   
   monoterpenes from fungal metabolism. An important goal for the research   
   team is to learn more about the metabolism of the spruce resin compounds   
   in the fungi and to find out whether this can be a detoxification reaction   
   for the fungus or for the beetle.   
      
       * RELATED_TOPICS   
             o Plants_&_Animals   
                   # Fungus # Trees # Insects_(including_Butterflies) #   
                   Microbes_and_More   
             o Earth_&_Climate   
                   # Geochemistry # Forest # Exotic_Species # Ecology   
       * RELATED_TERMS   
             o Beetle o Fungal_keratitis o Tree o Seed_predation o   
             Mountain_pine_beetle o Tropospheric_ozone o Aromatherapy o   
             Red-cockaded_Woodpecker   
      
   ==========================================================================   
   Story Source: Materials provided by   
   Max_Planck_Institute_for_Chemical_Ecology. Note: Content may be edited   
   for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Dineshkumar Kandasamy, Rashaduz Zaman, Yoko Nakamura, Tao Zhao,   
      Henrik   
         Hartmann, Martin N. Andersson, Almuth Hammerbacher, Jonathan   
         Gershenzon.   
      
         Conifer-killing bark beetles locate fungal symbionts by detecting   
         volatile fungal metabolites of host tree resin monoterpenes. PLOS   
         Biology, 2023; 21 (2): e3001887 DOI: 10.1371/journal.pbio.3001887   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/02/230221144356.htm   
      
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