Insect Interactions in Forest and Range Systems of the West: An Overview

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Insect Interactions in Forest and Range Systems
of the West An Overview

• By Jessica Dhaemers

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Outline

• Roles of insects in ecosystems
• Current forest conditions and relevance to insect
  outbreaks
• Forest insects with emphasis on bark beetles and
  spruce budworm current situation and management
• Range insects with emphasis on Mormon crickets
  historic uses and management
• Use of insects as biocontrol for invasive plant
  species example from Nevada
• Conclusions

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Roles of Insects in Ecosystems

• Aid in decomposition, increasing soil fertility
  and porosity, which can improve plant growth
• Herbivory reduce competition by reducing the
  number of plants or enhance vigor of some plants
  by feeding on but not killing them.
• Serve as food sources for many animal species
• Aid in dispersal of seeds, spores, and
  invertebrates within ecosystems
• Aid in pollination, which controls where plants
  occur
• (Views, 2001)

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Forest Composition and Structure

• Tree density has increased in some areas 9
  trees/ ha in pre-settlement era to over 300
  trees/ ha at present (Covington et al., 1994)
• Increase in shade tolerant species (Douglas-fir,
  white fir, black spruce and balsam fir) Canada
  and western U.S. (Galipeau et al., 1997 and
  Lesieur et al., 2002)
• Expansion of forests and woodlands in northwest
  U.S. with a shift from early to late seral
  species from the 1930s to the 1990s (Hessburg et
  al., 2000).
• A shift to more shade tolerant species in the
  Great Basin (Hessburg et al., 2000) .

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How is this relevant to insect outbreaks?

• Greater tree densities increase competition for
  water and nutrients and weaken trees defense to
  insect infestation. (Kerlin, 2001 and Powers et
  al., 1999)
• Shade tolerant trees are generally more
  susceptible to insect outbreaks. (Hessburg et
  al., 2000)
• Stand age can increase susceptibility to some
  insect species such as western spruce budworm and
  Douglas-fir bark beetle. (Hadley and Veblen, 1993)

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Bark Beetles

• Reproductive pheromones effectively carry 15-20
  feet forests with open stand structure are at
  less risk from large scale outbreaks (View,
  2001).
• Water stressed Douglas fir have been shown to
  accumulate ethanol within their tissue which
  attracts bark beetles to these trees (Kelsey and
  Joseph, 2001).
• Can complete two life cycles per year where
  temperature allows

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Alaska and Spruce Bark Beetles as an Example

• Two million acres were infested between
  1920-1990, with three million acres infested in
  the 1990s, and a peak of one million acres
  affected in 1996.
• Seventy to eighty percent of trees on the Kenai
  Peninsula have been killed.
• Epidemic outbreaks attributed to poor management
  tree crowding and increased susceptibility
  through competition for resources.
• Anchorage temperature increased 3.9 degrees F in
  last century beetles may complete two life
  cycles per year.
• (Kerlin 2001)

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Lake Tahoe and Bark Beetles

• Bradley and Tueller(2001) showed that prescribed
  burns in Jeffrey Pine caused significantly more
  beetle attack (24 of trees attacked in burn
  plots vs. lt1 in non-burned areas)Why?
• Rizzo and Maloney (1997-98 ground surveys)
  report a doubling of importance of white fir and
  incense cedar and a 50 decline in importance of
  Jeffrey pine and sugar pine
• An average of 25 tree mortality in lower montane
  forests with bark beetles as the greatest cause
• Highest mortality in trees 20-50 cm dbh
• White fir makes up highest percentage
• of dead stems (62-78)

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Management Options

• Integrated Pest Management (FS-98-42)
• Thinning
• Sanitation
• Lop and Scatter
• Pile and Burn
• Forest Practices Code of British Columbia (1995)
• Baiting
• Single tree treatment
• MSMA (Monosodium methanearsenate)
• Fall and burn
• Harvest
• Prevention
• Spraying susceptible tree species
• Carbaryl (Sevin)
• Permethrin (Astro, Dragnet)

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Spruce Budworm

• Wide range of host species
• Will top-kill larger trees or attack saplings
• Feed on foliage as well as flowers and cones
• Development is temperature dependent
• Predispose trees to other insect and fungal
  attack
• (Forest Insect and Disease Leaflet)

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Spruce Budworm in Colorado and New Mexico

• Swetnam and Lynch, 1989
• Colorado Front Range and New Mexico Sangre de
  Cristo Mountains
• Used tree-ring data to reconstruct outbreaks from
  1700-1983.
• Found increased synchronicity of outbreaks within
  these areas for the latter 20th century.
• Intensity was shown to increase after
• 1900.
• Why?

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Spruce Budworm in Western Montana

• Anderson et al., 1987
• Used tree-ring records to compare outbreaks from
  1814-1910 (pre-suppression) and 1911-1983.
• Found an increase in duration (from 13.3 years to
  25.4 years) and intensity (from 0.48 index value
  to 0.68) of outbreaks.

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Spruce Budworms and Bark Beetles in Colorado

• Hadley and Veblen, 1993
• Looked at stand response in the Colorado Front
  Range.
• Used tree-ring records to determine growth rates
  and insect outbreaks as well as written records
  from the Forest Service.
• Found that fire suppression was a secondary cause
  of the increased severity and synchronicity of
  insect outbreaks, and that stand structure/ age
  and tree density played a larger role in
  susceptibility of tree species to attack.

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Management Options

• Short Term
• Harvesting
• Spraying- malathion, carbaryl, or acephate
• Long Term
• Replanting non-host species
• Biocontrol
• Apanteles fumiferanae- wasp spp.
• Bacillus thuringiensis- bacteria

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Insects in Range Systems Mormon Crickets as an
Example

• Present since at least 200 BC
• Native tribes used this native insect as a food
  source
• Collection methods
• Uses
• Crickets considered a pest by USDA since late
  1800s.
• (DeFoliart 1994)

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Mormon Crickets

• Seven instars (growth stages) lifespan 100-120
  days
• Adults band together to migrate
• Can move up to one mile per day 25-50 miles
  seasonally
• At a density of one cricket/sq yd 38 lbs/acre
  dry weight consumed
• Outbreak densities can be greater than 100
  individuals/sq yd
• (U Wyoming Fact Sheet, 1994)

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Cricket Management Options

• Insecticides (U. Idaho reference page)
• Carbaryl bait
• Dimilin 2 sprayer application
• Malathion aerial application
• Biocontrol (Montana State University)
• Beauveria bassiana- Fungal pathogen

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Insects as Biocontrol of Invasive Plants
Examples from Nevada

• Preliminary Data
• Salt Cedar is an invasive tree in the western US
• Diorhabda elongata, Eurasian beetle common to
  native range and specific to saltcedar
• Released in 2001 in Lovelock, NV
• Over 200 ha defoliated in 2003 may release
  native plants from competitive pressure
• Insects are additional food source for rodents
  and birds
• Mortality expected to be slow and patchy
• (Dudley et al. 2004)

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Conclusions

• Insect interactions are natural processes in
  forest and range ecosystems
• Changes in forest structure and composition has
  increased susceptibility to large scale insect
  outbreaks
• Insect management is complex and difficult to
  implement on proper time scales
• Insect- plant interactions can be used in
  beneficial ways to influence species diversity
  and abundance

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Questions?