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Douglas-fir Tussock Moth - DFTM Orgyia pseudotsugata
DFTM Larva
DFTM LIFE CYCLE
First instarlarvae “Spinning down”which will “balloon” to new location
Douglas-fir Tussock Moth Larvae
“Red” trees caused by young larvae
Dead trees from older larvae.
Douglas-fir Tussock Moth - Male
Douglas-fir Tussock Moth – FemaleResting upon pupal case – note hairs
Egg cases
DFTMCAUSEDMORTALITY
Natural Control Factors
• Normally populations keep low during with over 90% of larvae and 75% of pupae are killed by natural factors.
• Viruses - Two naturally occurring types Nuclear polyhedrosis virus (NPV) and granulosis virus (GV)
NPV killed Douglas-fir tussock moth larva
NPV Particles – greatly enlarged
Natural Control Factors
Parasites: ManyDipterous parasitoid ovipositing onDFTM eggs
Natural Control Factors
Predators:
•Birds, especially Chickadees, small mammals and ants •Starvation – simply run out of leaves to feed on•High summer temperatures kill larvae•Withstand cold winter temperatures but not high
Outbreaks occur at about 9 year intervals & last 4 years
In the past, outbreaks often detected in year 3, treated in year 4
Pest Management – When & Why
Interactions - DFTM and Bark beetles
Pheromone traps – sticky glue & pheromone
When insects in traps begin to increase – then treat stand
Management Considerations
Chemical Control
Biological Control
DFTM Pheromones (Z) – 6-heneicosen-11-one
Nuclear polyhedrosis virus (NPV)Bacillus thuringiensis (Bt)
Will give good control if applied when the new foliage first appears.
Helicopter application of NPV
NPV Study - Control Plot (Not sprayed)
NPV Study - Treated with virus plot
Ecology
Stand Management
•In 1974 The EPA granted emergency authorization to the US Forest Service to use DDT for control of the Douglas-fir Tussock Moth
•Several hundred thousand acres were sprayed and the moth population crashed in the treated areas.
•Forest Service Researchers also established a “control” area of about the same size where no treatment was made.
•The Moth population crashed in those areas too.•This was the last legal use of DDT in the U.S.
Science vs Politics (Cost vs Benefit)
End of DouglasFir Tussock Moth Section