Douglas-fir Tussock Moth - DFTM Orgyia pseudotsugata

DFTM Larva

DFTM LIFE CYCLE

First instar larvae “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 – Female Resting upon pupal case – note hairs

Egg cases

DFTM CAUSED MORTALITY

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: Many Dipterous parasitoid ovipositing on DFTM 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 Douglas Fir Tussock Moth Section