Figure 5—Male beetle (about 8 times natural size) with its
“sawed-off,” concave rear end (about 13 times natural size) comprised
of segments, the largest of which bears a bump at the center of its up-

per margin,

Sometimes, however, only strips
or patches of the bole are attacked.
A healthy tree can recover if suffi-
cient areas of cambium (the layer of
growth cells) remain, and top-killed
trees can produce new leaders.
When the cambium heals over, a
brown pitch pocket marks the
injury. The usual evidence of such
attacks is roughened patches of bark
or scattered dead branches girdled
at the base by the egg galleries.

The fir engraver is frequently
associated with the roundheaded fir
borer, Tetropium abietis Fall, or the
flatheaded fir borer, Melanophila
drummondi (Kirby); however, the
winding larval galleries of both
borers are largely limited to the
lower, thick-barked areas of the
trunk. During outbreaks, the fir
engraver alone is generally responsi-
ble for most of the damage.

Life Cycle and Behavior

The adult fir engraver is a shiny
black beetle about 0.2 inch (4 mm)
long. Viewed from the side, it has an
incurved posterior with a small cen-
tral bump that is more pronounced
in the male (fig. 5).

In the summer, adults emerge
from infested firs and fly in search
of host material—not only standing
green trees but also freshly cut logs
and recent windthrows. Tempera-
ture probably determines when
adults emerge. Although flights can
occur from June to September,
most of them take place during July
and August.

Fir engravers seem to attack more
or less by chance rather than
because of any characteristic of the
host. But if the first beetles are able
to successfully bore without being
“pitched out,” they emit an attract-
ant that quickly lures many other
beetles. This mass attack will likely
occur when trees are already
stressed by drought, defoliation,
competition, dwarf mistletoe, or
root disease and will kill the host.

The female enters the tree first,
followed by the male. After the pair
mate, the female excavates an egg
gallery that is biramous from the
central nuptial chamber. The egg
gallery is anywhere from 4 to 12
inches (10 to 30 cm) long. During
the 5 to 7 weeks after mating, a
female will lay between 100 and 300
eggs in niches on either side of the
gallery.

5


Selected Bibliography

Berryman, Alan A. Population dynamics
of the fir engraver, Scolytus ventralis (Col-
eoptera:Scolytidae). I. Analysis of popula-
tion behavior and survival from 1964 to
1971. The Canadian Entomologist
105(11):1465-1488; 1973.

Ferrell, George T. Risk-rating systems for
mature red fir and white fir in northern
California. Gen. Tech. Rep. PSW-39.
Berkeley, CA: U.S. Department of
Agriculture, Forest Service, Pacific
Southwest Forest and Range Experiment
Station; 1980. 29 p.

Ferrell, George T.; Hall, Ralph C. Weather
and tree growth associated with white fir
mortality caused by fir engraver and
roundheaded fir borer. Res. Pap.
PSW-109. Berkeley, CA: U.S. Department
of Agriculture, Forest Service, Pacific
Southwest Forest and Range Experiment
Station; 1975. 11 p.

Moore, J.A.; Schenk, J.A.; Hatch, C.R.
Validation and refinement of a hazard
rating model for fir engraver-caused mor-
tality in grand fir stands, Forest Science
24(2):309-312; 1978.

Struble, George R. The fir engraver beetle,
a serious enemy of white fir and red fir.
Cir. 419. Washington, DC: U.S. Depart-
ment of Agriculture; 1937. 11 p.

Pesticides used improperly can be injurious to human beings, animals,
and plants, Follow the directions and heed all precautions on labels. Store
pesticides in original containers under lock and key—out of the reach of children
and animals—and away from food and feed.

Apply pesticides so that they do not endanger humans, livestock, crops,
beneficial insects. fish, and wildlife. Do not apply pesticides where there is
danger of drift when honey bees or other pollinating insects are visiting plants.
or in ways that may contaminate water or leave illegal residues.

Avoid prolonged inhalation of pesticide sprays or dusts: wear protective
clothing and equipment. if specified on the label.

If your hands become contaminated with a pesticide, do not eat or drink
until you have washed. In case a pesticide is swallowed or gets in the eyes.
follow the first aid treatment given on the label, and get prompt medical
attention. If a pesticide is spilled on your skin or clothing. remove clothing
immediately and wash skin thoroughly

NOTE: Some States have restrictions on the use of
certain pesticides. Check your State and local regula-
tions. Also, because registrations of pesticides are under
constant review by the U.S Environmental Protection
Agency, consult your local forest pathologist, county
agriculture agent, or State extension specialist to be sure
the intended use is still registered

Revised September 1986
Approved for Reprinting January 1991


Figure 4—A group of grand firs in Idaho displaying the variety of at-
tack patterns that characterize the fir engraver. One tree has lost its
top and some branches; its neighbor has been killed.

that are often formed when bark
beetles attack pines are not pro-
duced on firs.

Once under the bark, the adults
excavate egg galleries that engrave
the sapwood, the layer of wood
under the cambium (cover photo).
The egg gallery is horizontal, cutting
across the grain; the larval galleries
extend at right angles, along the
grain. This characteristic pattern
can be used to identify the fir
engraver (fig. 3).

Initial attacks in the crown may
girdle the branches, disrupting the
flow of water and nutrients and kill-
ing the branch. The appearance of
yellowed or red branches in an
otherwise green tree, commonly
called “flagging,” is the first easily
seen sign of infestation (fig. 4).

Numerous attacks over part or all
of the bole may kill the upper por-
tion of the crown or the entire tree
in a single summer. The foliage
turns yellow and then red over the 3
to 6 months after an attack.


Figure 6—Larvae at the end of their galleries beneath the bark of a
California red fir.

Four to six days after the female
begins boring the egg gallery, a
yellowish-brown discoloration ap-
pears on the surrounding area. The
stain is caused by the fungus
Trichosporium symbioticum Wright,
which is carried by the beetles.

The eggs incubate for 9 to 14
days. When they hatch, the larvae
mine straight up and down, perpen-
dicular to the egg gallery (fig. 6),
and pass through six molts.

Fir engravers overwinter mainly
as young or mature larvae. In the
spring, they feed for a short period
and then construct pupal cells at the
end of their galleries. Pupation
takes 7 to 14 days; in another 2
weeks, the adults are ready to
emerge from the tree.

It may take anywhere from 40 to
380 days for completion of the lar-
val stage. In warm locations, the fir
engraver completes one generation
and a partial second generation each

year. In cooler sites, such as north-
facing slopes above 6,000 feet (1,800
m) in the Sierra Nevada of Califor-
nia, the fir engraver needs 2 years to
complete its life cycle. Usually,
however, the fir engraver is con-
sidered to have one generation a
year.

Natural Control

Several insect predators and
parasites are commonly associated
with the fir engraver and occasional-
ly destroy a large part of the brood.
The more important predators in-
clude two beetles —the black-bellied
clerid (fig. 7) and the red-bellied
clerid—which prey on larvae and
adults. A major parasite of fir
engraver larvae is a braconid wasp.
The females of this wasp insert their
ovipositors through the bark and lay
their eggs directly on the developing
larvae. A mite and a nematode are


Forest Insect
& Disease
Leaflet 13

U.S. Department
of Agriculture
Forest Service

Fir Engraver

George T. Ferrell!

The fir engraver, Scolytus ven-
tralis LeConte, belongs to the fam-
ily of insects called bark beetles,
which live between the bark and
wood of host trees.

‘Entomologist, U.S. Department of
Agriculture, Forest Service, Pacific
Southwest Forest and Range Experiment Sta-
tion, Berkeley, CA. Previous editions of this
leaflet were written by Robert E. Stevens, a
retired Forest Service entomologist now with
Colorado State University, Fort Collins, CO.

A wide-ranging, native beetle, the
fir engraver attacks most species of
fir in the Western United States.
Epidemics can cause severe tree
mortality. From 1977 to 1978, for
example, the fir engraver killed an
estimated 1.2 million trees, totaling
114 million board feet (650,000 m3),
on the National Forests in northern
California. Other outbreaks have
been more localized, but the
resulting losses have still been



also important parasites on all
stages of the fir engraver.

These and other natural enemies,
especially woodpeckers, which
remove the outer bark to feed on the
larvae, may help to control the fir
engraver. However, they are not ef-
fective in preventing outbreaks.

Control

Fir engraver populations can be
effectively controlled in individual
trees:

© The infested tree can be felled
and the bark burned in place or the
bark peeled and then burned.

© The infested tree can be felled,
limbed, and left fully exposed to the
sun, provided the logs are rolled
every few days to expose all parts of
the bark.

© The infested tree or log can be
submerged in water for at least 6
weeks.

¢ The infested tree can be felled,
and the trunk sprayed with insec-
ticide using a low-pressure sprayer.

Over extensive areas, however,
reducing fir engraver populations is
more complicated. The fir engraver
habitually infests tops and scattered
patches of cambium. It is not prac-
tical to search out and remove the
many trees in a stand that might be
infested. Infested trees might con-
tain only a few active broods; such
trees often recover completely.

Silvicultural practices aimed at
maintaining healthy stand condi-
tions appear to offer the best chance
for minimizing engraver-caused
losses. Diseased, injured, or deca-
dent trees should be removed,
and overly dense stands should be
thinned to reduce tree competition.

Figure 7—Adult black-bellied clerid (two
times natural size) which feeds on larval and
adult fir engravers. This clerid is also a
predator of the western pine beetle.

Windthrown trees and cut logs
should be removed within the year,
before the beetles have had time to
produce new broods.

Assistance

Guides for assessing the risk or
hazard of fir engraver-caused mor-
tality to trees and to stands are
available and included in the
bibliography.

Information about fir engraver
control is also available from
Cooperative Extension agents, from
State foresters, or from Forest Pest
Management, U.S. Department of
Agriculture, Forest Service.


Figure 1—Grand fir killed by the fir engraver during the 1974 out-

break on the Nezperce National Forest in Idaho,

Figure 2— Distribution of the fir engraver.

2

severe. In New Mexico, some 37,000
trees were killed in 1954 on about
700 acres (2,800 ha) in the Cibola
National Forest.

Outbreaks characteristically oc-
cur at irregular intervals and have
been recorded at least once a decade
over the last 60 years (fig. 1).
Although no one knows exactly
when outbreaks will develop,
lowered resistance of the trees ap-
pears to be a contributing factor.
Some outbreaks, such as the
1977-78 outbreak in northern
California and the 1954 one in New
Mexico, have coincided with periods
of drought. Other outbreaks, such
as the one that occurred in 1974-76
in the Blue Mountains of Oregon
and Washington, have taken place
after outbreaks of defoliating
insects.


Figure 3—An egg gallery with an adult fir engraver and larvae at the
end of their parallel galleries.

When fir engraver populations
are endemic, trees are still killed,
but losses are less severe.

Hosts and Distribution

The fir engraver attacks primarily
white fir, grand fir, and red fir; its
range coincides with the distribution
of these three species. Fir engravers
are found from British Columbia
south to Baja California and east to
the Rocky Mountains (fig. 2).

The fir engraver also occasionally
attacks Douglas-fir, subalpine fir,
mountain hemlock, and Engelmann
spruce.

In addition to infesting standing
green trees, the fir engraver will at-
tack freshly cut logs and recent
windthrows.

Evidence of Attack

Fir engravers bore entrance holes
along the main stem, usually in
areas that are greater than 4 inches
(10 cm) in diameter. These holes are
about 0.1 inch (2 mm) wide and are
most often located in bark crevices
or in the roughened bark at the
junction of a branch and the trunk,
but other sites may be attacked as
well.

Reddish-brown or white boring
dust may be seen along the trunk in
bark crevices and in cobwebs.

Streams of clear pitch often flow
from the entrance holes down the
bole, and vigorous firs may exude
enough pitch to drown the beetles or
cause them to abandon their en-
trance holes. The creamy pitch tubes

3