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IntroductionBalsam Woolly Adelgid
• Introduced from Europe in early 1900’s
• Susceptible Species: – True firs (Abies sp.) in North America
Tree Symptoms: Crown Infestation
Gout Phase• swollen branch
nodes• stunted
terminal growth• Needle
Mortality• Bud
Suppression Photo: Robert L. Anderson, USDA Forest Servicewww.forestryimages.org
Tree Symptoms-stem infestation
Trunk Phase– rotholz (rot=red, holz=wood)
• Red-colored wood
– Purple patches beneath bark– Broken, blocky bark
Diseased Functions
• Tissues initially affected– Needles: mortality– Buds: suppression– Sapwood: uncontrolled, abnormal growth,
poor water conduction
• Impact on tree– crown deformity– dieback– predisposition to windthrow and root disease– death
Diseased Functions
• Impact on Forest– dependent on
climate, forest composition, site
– loss of dominant and co-dominant fir component
– change in species composition and age structure
Source: Greenbank, D.O. 1970. Climate and ecology of the balsam woolly aphid. Can. Ent. 102: 546-578.
Impact on Forest Maritime vs. Continental N.B.
Infestation Pattern
All trees crown and stem infestationsCrown infestations persist w/ new growth
Small, isolated patchesStem infestations on lower boleCrown infestations checked by cold winters
Characteristic Maritime Continental
Tree MortalityMost overstory trees killed or have dead tops
Some large diameter trees killed by stem infestationLow tree mortality
Regeneration Some severely gouted and killed
Regeneration by stem infested trees gouted
Primary Stress Agent
Balsam Woolly Adelgid -- Adelges piceae– Introduced from Europe ca. 1900 on
nursery stock to Maine and Nova Scotia
– On native silver fir does not cause significant damage
– North American host trees: Abies spp.
Photo: USDA Forest Service - Ashville Archives www.forestryimages.org
Pathogen
Signs• Eggs--up to 248 yellow eggs laid in waxy
wool-like extrusions• Larvae--3 larval instars• Adult-- approximately .8 mm long, covered in
waxy wool-like material
Photo:Scott Tunnock, USDA Forest Service, www.forestryimages.org
Photo: Jerald E. Dewey, USDA Forest Service, www.forestryimages.org
Environment
Host: True firs• balsam and Fraser in the east; sub-alpine,
Pacific silver and grand in the west
Native range of balsam fir (from silvics)
Environment
Distribution of Balsam Woolly AdelgidFrom BWA FIDL 1970
East CoastWest to east prevailing winds
limit inland spread
Environment
Moderate winters – Do not survive below -
30º F– Snow and tree
structures afford some protection from cold
Predisposing FactorsTree Adaptations
Introduced Pest North American firs highly
susceptible Site
Productive– Washington State, Pacific silver fir– Johnson et al. 1963
Well drained to dry– Newfoundland– Page 1975
Poorly drained– Maine– Brower 1947
Predisposing FactorsTree Adaptations
Age Related Factors – Initial infestations on larger trees
• Taller• Deeper Crowns • Larger Diameter
– More likely to have stem infestations– Ideal size around 30-40 years old
– Rough barked trees more susceptible (more protected locations)
– Younger, denser stands less susceptible
Predisposing FactorsDegree of Stress
Life Cycle Components Impacting Degree of Stress
• Eggs:average 100 eggs/female 1st gen (50, 2nd gen), some dispersal
• Larvae: Crawlers: mobile stage, dispersal, overwintering
• Adults: High reproductive capacity– Reproduction: parthenogenetic, no males
necessary, no need for mate finding or successful mating
• Multivoltinism
Predisposing Factors: Degree of Stress
Life Cycle (Maine: 2 generations/year)
Overwintering Neosistens
2nd, 3rd instars and adult
Eggs(June)
Break dormancy
Late April, early May
1st Instar(Crawler)
NeosistensHatch w/in several days
No molt
2nd, 3rd instars, adult*, eggs, 1st instar (crawler)
*2nd generation adults abundant late Sept; egg laying thru Mid-Nov.
From: F.P. Hain, 1988 in A.A. Berryman
Predisposing Factors: Degree of Stress
Mechanism of Disruption• Stem Infestation
– change in water transport structures• development of rotholz
– Reaction to chemicals in the insects’ saliva– Thick walled cells, wide rings– Similar to compression wood/heartwood
» poor water conduction
– physiological drought
Predisposing Factors: Degree of Stress
Mechanism of Disruption
Crown Infestation– change in wood
structure (rotholz)– old needles not
replaced– buds inhibited– loss of
photosynthesizing capacity
– gradual starvation
Predisposing Factors: Degree of Stress
Population ControlsWeather
• Early or late freezing temperature • 100% mortality of overwintering stage at -
30ºF, – NB study, ~40% died w/ low T of -22 º F (~80%
after 5 days of -22 ºF)– All other life stages die w/ prolonged temps <32
ºF, killed instantly @ -5 ºF– Cold winters with little snow cover
• Warmer climates see more generations/yr.
Predisposing Factors: Degree of Stress
Population ControlsNative Predatory Invertebrates/Introduced Predators
• Native natural enemies– Predatory mites– Lacewings (occasional)– Plant bugs (Mirids)– Coccinellids– Syrphids
• Most important natural enemy• Success limited by high level of parasitism
• Introduced biological control– 3 Coleoptera– 3 Diptera
http://www.rutkies.de/kaefer/Aphidecta%20obliterata%20-%20Gebirgsmarienkaefer%2001.html
http://photo.dipterologic.com/data/media/1/skuznetzov_syrphus_torvus_DSC072345.jpg
Predisposing Factors: Degree of Stress
Population ControlsNative Predatory Invertebrates/Introduced Predators
Issues• Generalist predators• Univoltine predators, multivoltine target• Do not feed on important life stages• Controls dependent on high adelgid populations• Cold tolerance of introduced controls• Introduced predators all adapted to feeding on stem infestations
Ideal• Specialist Predator
– Capable of surviving on low densities (and keeping densities low)– Capable of responding through increased fecundity or increased feeding
rate to growth of prey populations– Capable of active searching and feeding
• In diverse habitats (stem and twig) • On several life stages (esp. egg crawler)
• Parasitoid (no known on Adelginae)
http://cedarcreek.umn.edu/insects/album/029083009ap.html
Predisposing Factors: Degree of Stress
Population Controls
• Food availability and quality– After several years of infestation, changes
in the bark structure can make individual trees temporarily unsuitable
• Leads to decreased adelgid population• As cracks form, parenchyma is near surface
– Again suitable for adelgid– Possible for insects to build up from low level
populations on understory fir
Inciting Factors
• Arrival of crawler on suitable feeding site
• Insertion of stylet and change to neosistens (rotholz develops at this stage regardless of further survival of the insect)
Contributing Factors
• Drought• Ice and wind damage
– irregular crown shape contributes to predisposition to damage
• Fungal Infection– root rots (which further
predispose to windthrow)