Forest Health Fact Sheet
March 2017
The range of Pandora moth extends through most
western states. In Oregon, they are most often found in
areas with loose, volcanic soils such as central Oregon.
Biology
Eggs hatch in late summer and larvae begin feeding on
pine needles. When temperatures drop, larvae retreat to
the base of needles to overwinter and resume feeding the
following spring. The larvae are voracious eaters grow
from <1/4” to 3” as they develop through five molts.
Larvae may be brown, black or green and may have
patterns to blend in with pine branches. When ready to
pupate in their second summer, larvae will travel down
trees and burrow in the soil. They prefer loose, volcanic
soils and are often found in areas of historic volcanic
activity. The second winter is spent in the pupal stage
and adults emerge July - August. Adults often congregate
around light sources, sometimes far from host trees.
Adults have up to a 4” wingspan, and are grey-brown
with pink accents and a black spot on the underside of
each hind wing.
Damage
Older needles are preferred host material and buds are
untouched, therefore tree mortality is uncommon unless
combined with other factors such as drought, heavy
dwarf mistletoe infestation or physical damage. Mass
defoliation results in a “lion’s tail” appearance in
branches, caused by defoliation of just the older needles.
Pandora moth (Coloradia pandora linseyi) is our largest and
perhaps most charismatic forest insect pest. In its larval stage
it is a defoliator of pine trees. Outbreaks from this insect are
cyclical but highly variable in recurrence and duration.
Pandora moth has a 2-year life cycle, the defoliating larval
stage typically occurs in even number years. The last major
outbreak from this pest in Oregon was in Central Oregon from
1988-1996 but a small increase in populations was observed in
2016. This insect occurs where pine grows in loose, volcanic
soils. Mature larvae and pupae are traditional foods collected
by several Native American tribes such as the Paiute, Klamath
and Modoc.
Pandora moth larval color morphs and pupae
Clockwise: USFS R2, William Ciesla,
Darrell Ross (OSU), USFS R3, Bugwood.org
Hosts
Major: ponderosa, lodgepole and Jeffrey
pines
Minor: sugar pine
Pandora moth adult
William Ciesla, FH Mgt. Int., Bugwood.org
Defoliation represents a loss of photosynthetic tissue
which can cause growth loss.
Outbreak intervals can range from 9-156 years and each
individual outbreak typically lasts 5-8 years. Large
amounts of frass (larval droppings) are usually evident
on the forest floor during an outbreak. Outbreaks
typically collapse from predation by vertebrates and
invertebrates, parasitism and NPV (nuclear
polyhedrosis), a common disease in dense populations of
caterpillars.
Management
Silvicultural
Periodic thinning and mistletoe management will
improve resilience in trees, which allows them to
withstand mass defoliation during outbreaks.
Mechanical
Prescribed burns, conducted when larvae are traveling to
the soil to pupate or when pupae are in the ground, have
had variable success. Burning creates a wildfire risk and
causes damage to the tree, which reduces vigor and
resilience against defoliation.
Insecticides
Insecticides are typically not necessary because
outbreaks tend to collapse on their own due to natural
controls.
In severe outbreak scenarios treatment with insecticide
may be warranted. Bacillus thuringiensis (Bt) is an
effective insecticide with few non-target impacts.
Insecticides are most effective when applied in the
summer immediately before pandora moth larvae start
feeding. Small-scale applications can preserve foliage in
high-value areas. Annual applications of insecticides for
several years may be necessary to protect trees until an
outbreak subsides.
When using pesticides, always read and follow the label
Management
Avoid planting pine in rocky, harsh sites
Thin dense stands
Manage dwarf mistletoe
Apply Bt in the summer before larvae start to
feed (not necessary for small outbreaks)
“Lion’s tail” from heavy defoliation from pandora moth
during an outbreak
More information:
Oregon Dept. of Forestry, Forest Health
http://tinyurl.com/odf-foresthealth
2600 State St. Bldg. D, Salem, OR 97310
503-945-7200
Other references:
USFS Forest Health Protection
www.fs.usda.gov/goto/fhp/fidls
OSU Forestry Extension
http://extensionweb.forestry.oregonstate.edu/
William Ciesla, FH Mgt. Int., Bugwood.org
