Douglas-fir Tussock Moth - DFTM Orgyia pseudotsugata
First instar larvae “Spinning down” which will “balloon” to new location
Douglas-fir Tussock Moth – Female Resting upon pupal case – note hairs
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)
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
Pest Management – When & Why Outbreaks occur at about 9 year intervals & last 4 years In the past, outbreaks often detected in year 3, treated in year 4
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.
Ecology Stand Management
Science vs Politics (Cost vs Benefit) • 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.
End of Douglas Fir Tussock Moth Section