Download Insects as biotic disturbance agents

Insects as biotic disturbance agents
Allan Carroll
Associate Professor
 Lecture outline/goals:
o Forest disturbances: abiotic versus biotic
o Insects as biotic disturbance agents
o Insects and “forest health” in the headlines
o Forest health: what it really means
o Insects and forest disturbance
o Examples: the major groups
© A.L. Carroll
Wildfire, wind, etc.
Abiotic
 “Healthy” forests require change or disturbance
© D. Powell, USDA Forest Service, Bugwood.org
 Disturbance
= any discrete event that disrupts forest ecosystem,
community, or population structure and/or function
 Natural disturbance agents comprise mainly…
Insects & disease
Biotic
© A.L. Carroll
© A.L. Carroll
Timber volume (m3 × 106) lost per year
Relative impacts of abiotic versus insect disturbance in Canadian forests
100
 Insects have much greater
impacts than wildfire
 Disturbance annually affects
many thousands of hectares
50
 High public profile
o
“Forest health”
0
Source: National Forestry Database (http://nfdp.ccfm.org/)
© A.L. Carroll
Insects and “forest health” in the news:
the emerald ash borer
“Scientists Race to Prevent Ash Tree’s Extinction”, New York Times, Oct. 8, 2009
© D. Cappaert, Michigan State Univ., Bugwood.org
© J. O’Brien, USDA Forest Service, Bugwood.org
© J.W. Smith, USDA APHIS., Bugwood.org
© D. Cappaert, Michigan State Univ., Bugwood.org
Insects and “forest health” in the news:
the Sirex wood wasp
“Alien Wasp Kills Whole Forests”, ABC News, Mar. 8, 2006
© W. Cranshaw, Colorado State Univ., Bugwood.org
© D. Haugen, Bugwood.org
© D. Haugen, Bugwood.org
© D. Haugen, Bugwood.org
Insects and “forest health” in the news:
the spruce beetle
“Billions of Beetles, Wildfire Spread Imperil Northern Forests”, Associated Press, Aug. 23, 2009
© E.H. Holsten, USDA Forest Service, Bugwood.org
© W.M. Ciesla, Forest Health Mgmt Int, Bugwood.org
© A.S. Munson, USDA Forest Service, Bugwood.org
© E.H. Holsten, USDA Forest Service, Bugwood.org
Insects and “forest health” in the news:
the mountain pine beetle
© A.L. Carroll
“Beetles Take a Devastating Toll on Western Forests”, New York Times, Jul. 13, 2004
© A.L. Carroll
© A.L. Carroll
Forest health: a closer look
 One of the most widely used terms in ecosystem
management
 Often in the news
 Associated with:
o
o
o
o
Air pollution
Invasive species
Wildfires
Insect outbreaks
 Powerful personal imagery
 Connects fragility of “health”
with ecosystems
 Misused and abused…
© National Interagency Fire Center Archive, Bugwood.org
Healthy or unhealthy?
Natural forest:
 In timber supply area…
= pest
 In protected area…
= natural disturbance agent
or, if alien invasive,…
= pest
 In multiple use area…
= both
 Interpretation depends on
management objectives
© A.L. Carroll
Healthy or unhealthy?
Intensively managed forest:
 No pest impacts
 Meets management
objectives, but…
 Limited in all aspects of
ecological function
© S. Katovich, USDA Forest Service, Bugwood.org
Forest health: a functional definition
 Values create conflicts!
 Need a definition without human expectations…
A working definition:
 Forest ecosystems are healthy when their underlying
ecological processes operate within a natural range of
variability, so that on any temporal or spatial scale, they are
dynamic and resilient to disturbance
How do insects cause disturbance?
 Insect disturbance is the consequence of herbivory (consumption
of plant tissues)
 Herbivory causes growth loss, deformation,
and/or mortality of trees
o
o
Direct impacts (e.g. tissue loss)
Indirect impacts (e.g. pathogen transmission)
 Two major “guilds” of tree herbivores
o Foliage feeders (e.g. caterpillars)
• Most commonly cause growth loss
o
© A.L. Carroll
Stem feeders (e.g. bark beetles)
• Frequently associated with tree mortality
© A.L. Carroll
Herbivory: eat and grow
 Herbivory is mainly the job of the juvenile stages
 There are two distinct types of development by insects:
o Complete metamorphosis (holometaboly)
• Juvenile stage don’t resemble adults (e.g. larvae)
o
Incomplete metamorphosis (hemimetaboly)
• Juvenile stages do resemble adults (e.g. nymphs)
Holometabolous
Hemimetabolous
Nymph
Larva
© J.E. Dewey, USDA Forest Service, Bugwood.org
Adult
Pupa
© J.A. Payne, USDA, Bugwood.org
Adult
© USDA Forest Service, NE Archive, Bugwood.org
© USDA Forest Service, R4 Archive, Bugwood.org
© D. Riley, Univ. Georgia, Bugwood.org
Injury versus damage
 Injury (i.e. herbivory)
o
Physical or physiological
losses to trees caused by
insects (e.g. reduction in leaf
area or photosynthesis)
 Damage
o
Economic losses caused by
insects (e.g. reduction in yield
or quality)
Feeding
Yield loss?
(Injury)
(Damage)
© A.L. Carroll
© R.F. Billings, TX Forest Service, Bugwood.org
© W.M. Ciesla, Forest Health Mgmt Int, Bugwood.org
Injury does not always cause damage!
Sucking/galling insects
 Nature of feeding
o Piercing/sucking mouthparts
o Plant part specialists
o Often prefer healthy/
vigorous hosts
o Some species create galls as
shelters
 Nature of injury
o Nutrient loss
o Pathogen transmission
o Phytotoxins and allergic reactions
 Most serious pests are introduced
© W. Cranshaw, CO State Univ., Bugwood.org
Sucking/galling insects - examples
 Insect:
 Insect:
Balsam woolly adelgid (Adelges piceae)
 Hosts: all true firs
 Injury: deformation, mortality
Cooley spruce gall adelgid (Adelges cooleyi)
 Hosts: spruces, Douglas-fir
 Injury: aesthetic (i.e. visual)
© L. Livingston, ID Dept. Lands, Bugwood.org
© W. Cranshaw, CO State Univ., Bugwood.org
© NC Forest Service, Bugwood.org
© R.F. Billings, TX Forest Service, Bugwood.org
© E.R. Day, VA Polytechnic, Bugwood.org
Seed and cone insects
 Nature of feeding
o Direct or indirect feeding on tree
reproductive organs
o Obligate = feed only on seeds/cones
o Facultative = feed on seeds/cones when
available
 Nature of injury
o Reduced production of viable seed
required for:
• Preservation of genetic variation
• Response to climate change
© L.R. Barber, USDA Forest Service, Bugwood.org
Seed and cone insects - examples
 Insect:
 Insect:
Western conifer seed bug (Leptoglossus
occidentalis)
 Hosts: most conifers
 Injury: direct seed destruction
Fir coneworm (Dioryctria abietivorella)
 Hosts: most conifers
 Injury: indirect seed destruction
© USDA Forest Service, Odgen Archive, Bugwood.org
© L.R. Barber, USDA Forest Service, Bugwood.org
© M. Zubrik, Slovakia Forest Res. Inst., Bugwood.org
Root and lower stem insects
 Nature of feeding
o Commonly associated with fungi
o Root-feeding insects:
• Commonly associated with managed
stands, increasing importance in forestry
o Lower-stem insects:
• Commonly associated with mature stands
 Nature of injury
o Consumption of cambial tissues of roots and
lower stems
o Growth loss, deformation, occasional mortality
© G. Csoka, Hungary Forest Res. Inst., Bugwood.org
Root and lower-stem insects - examples
 Insect:
 Insect:
Warren’s root collar weevil
(Hylobius warreni)
 Hosts: lodgepole pine, spruce species
 Injury: mortality of young trees
Red turpentine beetle
(Dendroctonus valens)
 Hosts: lodgepole pine, ponderosa pine
 Injury: mortality of stressed trees
© Joseph Berger, Bugwood.org
© A.L. Carroll
© C. Hellqvist, Swedish Univ. Agric. Sci., Bugwood.org
© E.H. Holsten, USDA Forest Service, Bugwood.org
© A.L. Carroll
© USDA Forest Service, NE Area Archive, Bugwood.org
Shoot insects
 Nature of feeding
o Specialization on elongating shoots
o Preference for young, vigorous trees
 Nature of injury
o Growth loss, longer rotation
o Malformation
o Impacts greatest on young trees
o Indirect mortality - competition
o Injury often positively related to tree vigour,
increased by fertilization, irrigation, spacing
© E.B. Walker, VT Dept. Forests Parks & Rec., Bugwood.org
Shoot insects - examples
 Insect:
 Insect:
White pine weevil (spruce weevil)
(Pissodes strobi)
 Hosts: spruce and pine species
 Injury: growth loss, deformation
Bud moths (Zeiraphera spp.)
 Hosts: spruce and larch species
 Injury: growth loss, deformation
© A.L. Carroll
© S. Katovich, USDA Forest Service, Bugwood.org
© A.S. Munson, USDA Forest Service, Bugwood.org
© W.M. Ciesla, Forest Health Mgmt Int, Bugwood.org
© CT Agric. Exp. Stn. Archive, Bugwood.org
© A.L. Carroll
Woodborers
 Nature of feeding
o Develop in phloem and sapwood
o Associated with stressed, dead trees
o Attracted to volatiles associated with wood
deterioration
 Nature of injury
o Kill or weaken live trees (typically stressed)
o Some species associated with fungi
o Impact wood products
o Significant potential as invasive species
© D. Cappaert, Michigan State Univ., Bugwood.org
Wood borers - examples
 Insect:
 Insect:
Golden buprestid
(Buprestis aurulenta)
 Hosts: Douglas-fir, pine species
 Injury: sapwood boring (reduced integrity)
Striped ambrosia beetle
(Trypodendron lineatum)
 Hosts: most conifers
 Injury: sapwood boring (aesthetics)
© M. Jurc, Univ. Ljubljana, Bugwood.org
© S. Tunnock, USDA Forest Service, Bugwood.org
© A.L. Carroll
© M. Jurc, Univ. Ljubljana, Bugwood.org
© P. Kapitola, Czechia State Phytosan. Admin., Bugwood.org
Defoliators
 Nature of feeding
o General preference for young foliage
o Some species feed on old foliage
o Synchrony between egg hatch and bud
burst usually required
 Nature of injury
o Feeding causes loss of photosynthetic
organs
o General loss of tree vigour
o Growth reduction, crown deformation
o Occasional “top-kill” or mortality
o Several species prone to outbreaks
© A.L. Carroll
Defoliators - examples
 Insect:
 Insect:
Western spruce budworm
(Choristoneura occidentalis)
 Hosts: Douglas-fir, other conifers
 Injury: growth loss, mortality
Douglas-fir tussock moth
(Orgyia pseudotsugata)
 Hosts: Douglas-fir
 Injury: growth loss, mortality
© K.E. Gibson, USDA Forest Service, Bugwood.org
© D. Owen, CA Dept. Forestry and Fire Prot., Bugwood.org
© S. Tunnock, USDA Forest Service, Bugwood.org
© W.M. Ciesla, Forest Health Mgmt Int, Bugwood.org
© D. McComb, USDA Forest Service, Bugwood.org
Bark beetles
 Nature of feeding
o General preference for older trees
o Feed beneath bark on phloem tissues
o Complex adaptations to overcome tree
defenses
 Nature of injury
o For many species, successful
reproduction requires tree death
o Close association with pathogenic fungi
o Several species prone to outbreaks
© A.L. Carroll
Bark beetle impacts in recent decades
Bark beetles - examples
 Insect:
 Insect:
Mountain pine beetle
(Dendroctonus ponderosae)
 Hosts: pine species
 Damage: tree mortality
Spruce beetle
(Dendroctonus rufipennis)
 Hosts: spruce species
 Damage: tree mortality
© E.H. Holsten, USDA Forest Service, Bugwood.org
© A.L. Carroll
© A.L. Carroll
© E.H. Holsten, USDA Forest Service, Bugwood.org
© A.L. Carroll
© W.M. Ciesla, Forest Health Mgmt Int, Bugwood.org
Some final words…
 Insects can inflict injury to all parts of a tree
 Disturbance arising from injury extends across spatial scales –
from trees to landscapes
 Insect disturbance is a critical component of forest health
 Most insect herbivory is natural, some is associated with
introduced species
o
Management objective and actions must vary accordingly
Thank you!
© A.L. Carroll