1
Screening Aid
This CAPS (Cooperative Agricultural Pest Survey) screening aid produced for and distributed by\
:
USDA-APHIS-PPQ National Identification Services (NIS)
This and other identification resources are available at: http://caps.ceris.purdue.edu/taxonomic_services
Joseph Benzel
1) Identification Technology Program (ITP) / Colorado State University, USDA-APHIS-PPQ-Science & Technology (S&T), 2301 Research
Boulevard, Suite 108, Fort Collins, Colorado 80526 U.S.A. (Email: itp@USDA.gov)
The great spruce bark beetle, Dendroctonus micans (Kugelann) (Fig.
1), is a widely distributed pest in Europe and Asia. The primary host
of this species is spruce ( Picea ) but it will also infest a variety of other
conifer species including pine ( Pinus ) and Douglas fir ( Pseudotsuga ).
The adults and larvae feed in the cambium of the trunk (Figs. 2 and 4),
damaging the tree by girdling it and spreading pathogenic fungi (Fig.
3).
Dendroctonus micans is a member of the Curculionidae (subfamily
Scolytinae) which is comprised of weevils and bark beetles. Members
of this family are highly variable but almost all species share a distin\
ct
club on the end of their antennae consisting of three segments. The
Scolytinae, to which Dendroctonus belongs, consists of the bark
beetles. In general, members of Scolytinae are small (
pill shaped beetles of a reddish brown or black color. Some authors
consider Scolytinae to be a distinct family (Scolytidae).
The genus Dendroctonus contains twenty species, thirteen of which
are native to North America. The genus is primarily Nearctic in its
distribution with the six non-native species occurring in Eurasia. It can
be distinguished by the procurved and armed elytral bases, a convex
frons modified by grooves and ridges, hairlike vestiture, and a five
segmented antennal funicle
Dendroctonus micans has not yet been detected in the United States.
A quality, high powered microscope is required to examine the
characters necessary to identify these beetles.
This aid is designed to assist in the sorting and screening of D. micans
suspect adults collected through visual survey in the continental
United States. It covers basic Sorting of traps, Level 1, and Level 2
screening, all based on morphological characters. Basic knowledge of
Coleoptera morphology is necessary to screen for D. micans suspects.
Fig. 1: Dendroctonus micans in
tree (photo by Jacques Regad,
Département de la Santé des Forêts,
Bugwood.org).
Fig. 2: Dendroctonus micans gallery
(photo by Beat Forster, Swiss Federal
Institute for Forest, Snow and
Landscape Research, Bugwood.org).
Version 5
18 June 2015
Great Spruce Bark Beetle
Dendroctonus micans (Kugelann)
Coleoptera Scolytinae
2
Sorting
Insects collected during Dendroctonus micans surveys should be sorted initially for the presence of
beetles of the appropriate size color and shape.
1. Beetles are between 6 mm (0.5 inches) and 8 mm (0.7 inches) in length.
2. Beetles are pill-like in shape.
3. Beetles are black, reddish-brown, or tan colored.
Beetles meeting these requirements should be forwarded to Level 1 Screening (Page 3).
Fig. 3: Tree attacked by Dendroctonus micans . During a bark
beetle attack trees will show little sign of damage other than a
series of small bore holes. Often it is not apparent that bark beetles
have infested a tree until after they have emerged from it (photo by
Stanislaw Kinelski, Bugwood.org).
Fig.4: Dendroctonus micans larvae in gallery. Unlike most other
scolytids, Dendroctonus larvae feed in a single large communal
gallery rather than in individual galleries. Other unique behaviors
include facultative inbreeding in D. micans and the closely related
D. punctatus (photo by Louis-Michel Nageleisen, Département de
la Santé des Forêts, Bugwood.org).
Great Spruce Bark Beetle
Dendroctonus micans (Kugelann)
Coleoptera Scolytinae
3
Level 1 Screening
Suspect adults should be pointed and properly labeled. Level 1
Screening is based on characteristics of the antennae and general
dorsal surface.
Antennae
Scolytids have relatively stout, geniculate, clubbed antennae. The
clubs are made up of three antennomers and can be solid, annulated,
or occasionally lamellate. The scape will always be noticeable if not
well developed (Fig. 5). Dendroctonus species have a five segmented
antennal funicle and an oblong flattened club.
General Dorsal Surface
Beetles in the tribe Hylurgini have the basal margins of their elytra
procurved and armed with a row of crenulations (Fig. 6). The
scutellum of tribe members is usually large and flat and the head is
usually concealed at least partially by an enlarged pronotum. The
anteriolateral areas of the pronotum are unarmed.
Fig. 5: Antennae of Dendroctonus sp.
Note the scape and large three part
club and five segmented funicle.
Fig. 6: Pronotum, base of elytra and
scutellum of Dendroctonus sp. Note
the row of crenulations along the
elytral margins .
Figs. 7-8: Dorsal views of the
common native Dendroctonus species
D. pseudotsugae and D. ponderosae.
These two species rank among the
most destructive scolytid species
currently present in the United States.
Fig. 8: Dendroctonus ponderosae Fig. 7: Dendroctonus pseudotsugae
Great Spruce Bark Beetle
Dendroctonus micans (Kugelann)
Coleoptera Scolytinae
4
Level 2 Screening
Level 2 screening is designed to screen out potential D. micans (Fig.
9) from other members of the genus (Figs. 7, 8, and 11). Screening is
based on features of the frons and stria patterning of the elytral decli\
vity.
It should be noted that the widespread native species D. punctatus is
almost identical in form to D. micans (Figs. 9-10). The two can only be
differentiated through careful examination by a scolytid expert, or through
genetic testing. Dendroctonus micans is 6-8 mm in length.
Frons
The frons of D. micans lacks a median groove and any form of lateral
expansion. The epistomal process is rather narrow and flattened. The
frons is smooth and polished interrupted only by deep close punctures.
Distance between the eyes is at least three times an eye width (Fig. 12).
Other Dendroctonus species have variable frons and epistoma (Fig. 13-
17).
Elytral Declivity
The interstriae on the D. micans declivity are smooth and shining. The
strial punctures are rather large, at least three times the size of the
interstriae (Fig. 18). Other Dendroctonus species have dull decliveties or
smaller punctures (Figs. 19-21) .
Fig. 9: Dendroctonus micans (target) Fig. 10: Dendroctonus punctatus
Fig. 11: Dorsal view of the common
Nearctic species Dendroctonus
rufipennis . This species is one of the
most destructive beetles currently in
the US. At times it can be difficult to
distinguish from D. micans but the red
colored elytra of the former allow for
easy identification.
Figs. 9-10: Dendroctonus micans (far
left) and D. punctatus (left) dorsal
surfaces. These two bark beetles
are almost identical in appearance
and separation is only through
careful comparison or genetic
testing. Dendroctonus punctatus is
widespread but uncommon across the
Nearctic.
Great Spruce Bark Beetle
Dendroctonus micans \(Kugelann\)
Coleoptera Scolytinae
5
Fig. 18-21 (right): Declivities of
assorted Dendroctonus species.
Note the smooth shining declivity of
D. micans with large strial punctures
Level 2 Non-targets
Fig. 19: Dendroctonus rufipennis
Fig. 15: Dendroctonus ponderosae Fig. 16: Dendroctonus pseudotsugae
Suspect D. micans specimens
(hylurgini with five segmented
funicles, a shining polished
frons with dense punctures but
no median groove, and large
shining strial punctures on the
declivity) should be sent forward
for identification. Specimens must
be labeled and carefully packed to
avoid damage during shipping.
Fig. 13: Dendroctonus punctatus.
Fig. 17 Dendroctonus brevicomis
Fig. 21: Dendroctonus brevicomis
Fig. 14: Dendroctonus rufipennis Fig. 12: Dendroctonus micans (target).
Figs. 12-17 (above): Dendroctonus
frons. Note the smooth shining frons
of D. micans (top left). adorned
only with a series of deep close
punctures.
Fig. 18: Dendroctonus micans (target)
Fig. 20: Dendroctonus ponderosae
Great Spruce Bark Beetle
Dendroctonus micans \(Kugelann\)
Coleoptera Scolytinae
6
Key and References
Key to Sort and Screen Dendroctonus micans Suspects in the United States
1. Beetles approximately 6-8 mm long; pill shaped and with black, brown, or tan coloration .............. 2
1’. Beetles larger or smaller than 6-8 mm long; not pill shaped; or color not a shade of black,
brown, or tan ........................................................................\
........................................ Not D. micans
2. Antennae geniculate with a large club made up of three segments on the end (Fig. 5); anterior
margins of elytra armed with a crenulate ridge and procurved (Fig. 6); scutellum small; head not
covered by pronotum; antennal funicle five segmented .................................................................. 3
2’. Antennae not geniculate or without a large club made up of three segments on the end; basal
margins of elytra unarmed and forming straight transverse line across the body; scutellum large;
head may or may not be covered by pronotum; funicle not five segmented, club not
flattened ........................................................................\
.............................................. .Not D. micans
3. Frons smooth and shiny with close deep punctures but no medial groove (Fig.12); distance
between eyes at least three times eye width; declivity smooth and shining with large
punctures (Fig. 18) ........................................................................\
...................... D. micans suspect
3’. Frons dull or armed with granules or medial groove (Figs. 14-17). Declivity with interstria
dull or strial punctures not wider than those of interstria ............................................ Not D. micans
Citation
Benzel, J. S. 2015. Screening aid: Great Spruce Bark Beetle, Dendroctonus micans (Kugelann). Identification Technology
Program (ITP), USDA-APHIS-PPQ-S&T, Fort Collins, CO. 6 pp.
References for more information on Dendroctonus micans and non-targets
Anderson, R. S. 2002 . Family 131 Curculionidae. Pp. 722-815. In Arnett R. H. American Beetles: Volume II. CRC Press.
Boca Raton, Florida. 861 pp.
Armendariz-Toledano, F. Nino, A. Sullivan, B. T. Kirkendall, L. R. Zuniga, G. 2015 . A new species of bark beetle
Dendroctonus mesoamericanus sp. nov. (Curculionidae: Scolytinae ), in southern Mexico and Central America. Annals of
the Entomological Society of America. 108 (3). 403-414.
CERIS. 2011. Exotic Wood Borer/ Bark Beetle Survey Reference: Dendroctonus micans. https://caps.ceris.purdue.edu/
dmm/1979.
Six, D. L, & Bracewell, R. 2015. Dendroctonus, Pp. 305-350. In Vega, F. E., & Hofstetter. R. W. Bark Beetles: Biology and
Ecology of Native and Invasive species. Academic Press, Elsevier. Amsterdam, Netherlands. 620 pp.
Wood, S. L. 1982. The Bark and Ambrosia Beetles of North and Central America (Coleoptera: Scolytidae) a taxonomic
monograph. Great Basin Naturalist Memoirs No 6 . pp. 151-203.
Acknowledgments
Funding for this project was provided to J. S. Benzel through section 10201 of the FY2014 Farm Bill. I would like thank
Terrence Walters (USDA-APHIS-PPQ-S&T ITP) and USDA-APHIS-PPQ National Identification Services for support of this
work and access to imaging equipment. Boris Kondratieff, Donald Bright, and Todd Gilligan (Colorado State University)
provided advice on species identification, image editing, and screening aid formatting.
Great Spruce Bark Beetle
Dendroctonus micans (Kugelann)
Coleoptera Scolytinae
