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Herbivory and Disturbance

Lecture outline/goals:​

  • How do insects cause disturbance?
  • Herbivory
  • Forest insect “guilds”
  • Examples

Injury versus Damage​

Injury (herbivory, disease)​

  • Physical or physiological losses to trees caused by biotic agent (e.g., reduction in leaf area or photosynthesis)

Damage:​

  • Economic losses caused by insects (e.g., reduction in yield or quality at time of harvest)

Insect diversity and abundance​

  • Insects account for most (53% of abundance) animals on earth
  • There are ~1 million described (~30 orders)
    • Estimated 5-30 million
  • ~60,000 invertebrates in BC
    • ~35,000 insects
  • less than 1% of insects considered pests

Herbivory and disturbance​

disturbance = any discrete event that disrupts forest ecosystem, community, or population structure and/or function

  • Insect disturbance is the consequence of herbivory (consumption of plant tissue)
  • Herbivory causes:
    • Growth loss
    • Deformation
    • Mortality
      • E.g., phloem herbivory
  • Herbivory is mainly by juvenile stages
    • Especially for holometabolous insects
      • Juvenilles Basically bags with mouths that try to eat as much as possible
      • Adults are specialized in reproduction and dispersal

Insect Herbivore "Guilds"​

  • Guild = Any group of species that exploit the same resource, or that exploits different resources in related ways
  • Forest insect herbivore guilds:
    • Sucking and galling insects
    • Seed and cone insects
    • Root and lower-stem insects
    • Shoot feeders
    • Woodborers
    • Defoliators
    • Bark beetles (bole feeders)

Group 1: Sucking / galling insects​

Nature of feeding​

  • Piercing/sucking mouthparts
    • Positive pressure in phloem is like a firehose to the small insects
      • Can't possibly digest all the sugar
  • Plant part specialists
  • Often prefer healthy/vigorous hosts
  • Some species create galls as shelters

Nature of injury​

  • Nutrient loss
  • Pathogen transmission
  • Phytotoxins and allergic reactions
  • Most serious pests are introduced and invasive

Examples:​

Insect: Balsam woolly adegild (Aldelges piceae) Hosts: all true first Inury: Deformation, mortality

Insect: Cooley spruce gall adelgid (Adelges cooleyi) Hosts: spruces, Douglas-fir Injury Aesthetics (i.e., visual)

Group 2: Seed and cone insects​

Nature of feeding​

  • Direct or indirect feeding on tree reproductive organs
  • Obligate = Feed only on seeds/cones
  • Facultative = feed on seeds/cones when available

Nature of injury​

  • Reduced production of viable seed

Examples:​

Insect: Western conifer seed bug (Leptoglossus occidentalis) Hosts: Most conifers Injury Direct seed destruction

Group 3: Root and lower stem insects​

Nature of feeding:​

  • Commonly associated with fungi
  • Root-feeding insects:
    • Greatest injury to managed stands; increasing importance in forestry
  • Lower-stem insects
    • Most commonly associated with mature stands

Nature of injury​

- Consumption of cambial tissues of roots and lower stems

  • Growth loss, potential mortality

Examples:​

Insect: Warren's root collar weevil (Hylobius warreni) Hosts: Lodgepole pine, spruce species Injury: Mortality of young trees

  • Not much of an issue for mature trees; becomes problematic when it feeds on young trees; Feeds on base of root collar, girdling young trees
  • Issue where mountain pine beetle has ravaged landscape
    • When we plant near these areas with new pine, Warren's root collar weevil will migrate to our new saplings

Insect: Red turpentine beetle (Dendroctonus valens) Hosts: Lodgepole pine, ponderosa pine Injury: Mortality of stressed trees Notes: From oregon, invasive to China; not much of an issue in North America

Group 4: Shoot insects​

Nature of feeding:​

  • Specialization on elongating shoots
  • Preference for young, vigorous trees

Nature of injury:​

  • Growth loss, longer rotation
  • Malformation
  • Impacts greatest on youngest trees
  • Injury often positively related to tree growth:
    • Making trees grow faster will often worsen disease

Examples:​

Insect: White pine weevil (spruce weevil) (Pissodes strobi) Hosts: Spruce and pine species Injury: growth loss, deformation Notes: Minimum 2 year growth loss

Insects: Bud moths (Zeiraphera spp.) Hosts: Spruce and larch species Injury: growth loss, deformation

Group 5: Woodborers​

Nature of feeding​

  • Develop in phloem and sapwood
  • Associated with stressed, dead trees
  • Attracted to volatiles associated with wood deterioration
    • E.g., ethanol

Nature of injury​

  • Kill or weakn live trees (stressed)
  • Some species associated with fungi
  • Impact wood products
  • Significant potential as invasive species

Examples:​

Insect: Golden buprestid (Buprestis aurulenta) Hosts: Doug fir, pine species Injury: Sapwood boring

Weird lifestage:

  • Can grow in freshly cut lumber, if not kiln dry
  • Once it grows into wood, it might not emerge for over 40 years
  • Can emerge from wood that's used in building

Insect: Striped ambrosia beetle (Trypodendron lineatum) Hosts: Most conifers Injury: Sapwood boring

Are farmers: They bore to grow fungi, they harvest, and use to feed their offspring

  • Offspring dont do anything but wait for food

Group 6: Defoliators​

Nature of feeding:​

  • General preference for young foliage
  • Some species feed on old foliage

Nature of injury​

  • Feeding causes loss of photosynthetic organs

Examples:​

Insect: Western spruce budworm (Choristoneura occidentalis) Hosts: Douglas-fir, other conifers Injury: Growth loss, mortality

Insect: Western hemlock looper (Lambdina fiscellaria lugubrosa) Hosts: Western hemlock, other conifers Injury: growth loss, mortality

Group 7: Bark Beetles​

Nature of feeding​

  • General preference for older trees - Feed beneath bark on phloem tissues
  • Complex adaptations to overcome tree defenses
    • When faced with defensive efforts form the tree, their able to digest many tree defence chemicals and synthesis them into useful chemicals
  • Nature of injury
    • For many species, succesful reproduction requires tree death
    • Close association with pathogenic fungi
      • Can't live without it
    • Several species prone to outbreaks
    • Population eruptions commonly associated with tree stress

Examples:​

Insect: Mountain pine beetle (Dendroctonus ponderosae) Hosts: Pine species Damage: Tree mortality

Female beetles initiate aggregation to the tree, produce aggregation pheremones;

  • Attracts more beetles
  • Produces more beetles
  • Creates positive feedback loop

Insect: Spruce beetle (Dendroctonus rufipennis) Hosts: Spruce species Damage: Tree mortality