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

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 Outline

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)

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).

How is this relevant to insect outbreaks? Greater tree densities increase competition for water and nutrients and weaken tree’s 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)

Bark Beetles Reproductive pheromones effectively carry 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

Alaska and Spruce Bark Beetles as an Example Two million acres were infested between , with three million acres infested in the 1990’s, and a peak of one million acres affected in 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)

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. <1% in non-burned areas)…Why? Rizzo and Maloney ( 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 cm dbh –White fir makes up highest percentage of dead stems (62-78%)

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)

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)

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 Found increased synchronicity of outbreaks within these areas for the latter 20 th century. Intensity was shown to increase after Why?

Spruce Budworm in Western Montana Anderson et al., 1987 Used tree-ring records to compare outbreaks from (pre-suppression) and 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.

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.

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

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 1800’s. (DeFoliart 1994)

Seven instars (growth stages); lifespan days Adults band together to migrate Can move up to one mile per day; 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) Mormon Crickets

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

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)

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

Questions?