Bark Beetles in the Genus Dendroctonus
setae equipped with projections pointed backward
(to the base, or away from the point) that cause them
to remain imbedded once contact with them is made.
Presumably they function in defense, especially
against vertebrate predators. Structures bearing such
projections are said to be barbed, and the occurrence
of numerous setae is ­sometimes described as barbate.
A small barb is called a barbule.
Barber, Herbert Spencer
Herbert Barber was born in South Dakota on April
12, 1882. His father, an engineer, encouraged his
son’s interest in natural history. At the age of 16 he
was given employment as an insect preparator at the
U.S. National Museum. He worked at such tasks as
arranging the Hubbard and Schwarz ­collection of
Coleoptera, but including a collecting trip with
Schwarz to Arizona and New Mexico. Although he
was employed continuously at the museum until
retirement, his pay was, after some years, and until
his retirement, provided by the U.S. Department of
Agriculture. In time, by association with entomo­
logists and through experience, he began to ­publish
results of his own studies. His publications eventually
amounted to some 90 papers. One of the most
intriguing was on his ­discovery of the strange life history of Micromalthus (Coleoptera: Micromalthidae)
in which there are several forms of larvae, and that
some larvae may produce eggs and larvae. He died
in Washington, DC, on June 1, 1950.
Reference
Mallis A (1971) Herbert Spencer Barber, pp 281–283. In:
American entomologists. Rutgers University Press, New
Brunswick, NJ, 549 pp
Barberry Whitefly, Parabemisia
myricae (Kuwana)
A whitefly (Hemiptera: Aleyrodidae) pest of citrus.
 Citrus Pests and Their Management
B
Bark Beetles
Some members of the subfamily Scolytinae (order
Coleoptera, family Curculionidae).
 Beetles
 Bark Beetles in the Genus Dendroctonus
Bark Beetles in the Genus
Dendroctonus
barbara j. bentz
U.S. Department of Agriculture Forest Service,
Logan, UT, USA
The genus Dendroctonus (Coleoptera: Curculionidae, Scolytinae), originally described by Erichson in
1836, currently includes 19 species that are widely
distributed. Seventeen species occur between Arctic
North America and northwestern Nicaragua, and an
additional two species are in northern Europe and
Asia. Dendroctonus species attack and infest conifer
hosts (Pinaceae) in the ­genera Larix, Picea, Pinus,
and Pseudotsuga. ­Species within the genus can be
identified by the host ­species they attack, egg gallery
patterns, population behavior, and morphological
distinctions. The smallest ­species is D. frontalis (male
length 2.0–3.2 mm) and the largest is D. valens (male
length 5.3–8.3 mm). ­Members of the Dendroctonus
genus, which means “tree killers,” are noted as the
most economically and ecologically significant species affecting forest ecosystems in western North
America. Tree ­mortality resulting from Dendroctonus outbreaks can adversely affect timber management, forest planning, and recreational opportunities.
In contrast, disturbance events caused by native bark
beetle species are important drivers of forest succession, foster heterogeneity and biodiversity, promote­
­biomass recycling, and play a critical role in the fire
ecology and overall health of many ecosystems.
Dendroctonus beetles are monogamous, and
spend the majority of their lifecycle in a cryptic
habitat beneath the bark of host trees where larvae
feed within the inner bark or phloem. Relative to
the length of their life cycle, only a short time is
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B
Bark Beetles in the Genus Dendroctonus
spent as an adult moving from tree to tree. The
majority of the species in this genus is capable of
killing the host tree in one generation. In fact, death
of the host is often a requirement for successful
brood production. Although most of the species
are capable of attacking and killing standing,
­vigorous trees, recently fallen trees are favored by
some species. The female is the colonizing sex in
the majority of Dendroctonus species. After attack
of a new host, mating typically occurs in a nuptial
chamber beneath the bark and an egg gallery is
­initiated. Adults of a few species, however, mate
before emerging from the brood host. Eggs are laid
either singly along the sides of the gallery, or in
clumps. Egg galleries may be either vertical or
­sinuous, and larvae mine and feed horizontally in
the phloem, either singly or en mass, depending on
the species. Pupation takes place in individual
niches within the phloem or in the outer bark of
the host tree. Upon adult emergence, which is usually ­temperature dependent, beetle dispersal to a
new host occurs and the process begins again.
Aggregation, which facilitates host selection
and mating, is an important life history strategy of
most, although not all, Dendroctonus species.
Aggregation is often a response to chemicals
­produced by the host tree, adults from the same or
a different species attacking the host tree, microbes,
or a combination of these factors. Aggregation on
a single host tree allows for a mass attack by
­conspecific beetles, thereby overcoming the resin
defensives of the conifer hosts. To overcome the
defenses of healthy, vigorous hosts, many beetles
must attack within a short time (1–3 days). Conversely, trees of poor health may be overcome by
fewer beetles (e.g., endemic population levels).
Because a single tree is a limited resource, some
Dendroctonus species have evolved a response to a
series of chemicals that interrupt aggregation.
These chemicals act to space beetle attacks along a
single tree and signal incoming beetles to begin
attack on another, nearby tree. Synthetic forms of
both attractive and interruptive aggregation chemicals have been developed for many Dendroctonus
species. The attractive aggregant chemical(s) are
commonly used, often with traps, for monitoring
and control of many economically important
­species in the genus. The complexity of the signal
for interruption of aggregation has made it difficult
to identify the chemical makeup of compounds, as
well as, the specific biological action of the
­compounds within the population ecology of
many Dendroctonus species. Consequently, the
current use of synthetic interruptive aggregation
chemicals is limited.
As with most poikilothermic organisms, temperature is a strong driving force of Dendroctonus
population dynamics and an important controller
of seasonality. Diapause, which is often temperature related, is typically considered the universal
adaptation of insects for maintaining seasonality.
However, with the exception of an adult reproductive diapause in D. rufipennis and D. pseudotsugae,
and a prepupal diapause in D. rufipennis, this
physiological timing mechanism appears to be
absent in the Dendroctonus genus. Instead,
­Dendroctonus seasonality appears to be under
direct temperature control. Life cycle duration in
the genus is variable depending on the species,
latitude, elevation, and microclimate of the population. Species in the south can have as many as
seven ­generations per year, whereas in the north,
or at high elevation some species require up to 3
years to ­complete a single generation. Intraspecific
lati­tudinal differences in many temperature-­
associated life history traits exist as well. Global
climate warming will undoubtedly have significant
impacts on the distribution and seasonality of the
Dendroctonus species.
Many Dendroctonus species carry spores of
symbiotic fungi either passively on the exoskeleton or in specialized structures of the integument
called mycangia. The fungi are disseminated
among host trees via adult Dendroctonus beetles.
Although little research has been conducted on
fungal associations of the majority of Dendroctonus species, the work that has been done shows
both a benefit and a detriment to the beetle,
depending on the particular fungal associate.
­Benefits gained include protecting the beetle brood
Bark-Lice, Book-Lice or Psocids (Psocoptera)
from other antagonistic associates, aiding beetles
in overcoming host tree defenses through pathogenic action of the fungi, altering the moisture
composition of the phloem, and providing or
­concentrating nutrients essential for reproduction
or development.
Native Dendroctonus bark beetles play significant roles in long term forest ecosystem function
and structure. However, forest conditions in many
parts of the Dendroctunus range in North America
have changed from conditions that existed prior to
pre-European colonization. The result is large
­landscapes vulnerable to Dendroctonus outbreaks
which are often in conflict with current land use
objectives. The formulation of effective management strategies for Dendroctonus populations
requires careful consideration of all aspects of land
use including timber production, the urban/wildland interface, wilderness, watershed, recreation
and wildlife. Synthetic attractive and interruptive
­aggregation chemicals and silvicultural options
are available for some species to aid in the prevention and suppression of large scale outbreaks. Any
action, including no action, should be tightly tied
to the management objectives for the landscape
under ­consideration. Restoration of the landscape
to reestablish ecological integrity after an outbreak
is also important for maintaining long-term
­ecosystem health.
 Mountain Pine Beetle
 Douglas-Fir Beetle
 Roundheaded Pine Beetle
References
Coulson RN, Witter JA (1984) Forest entomology, ecology
and management. Wiley, New York, NY, 669 pp
Mitton JB, Sturgeon KB (1982) Bark beetles in North
­American conifers, a system for the study of evolutionary biology. University of Texas Press, Austin, TX
Schowalter TD, Filip GM (1993) Beetle-pathogen interactions in conifer forests. Academic Press, London, UK.
252 pp
Samman S, Logan J (2000) Assessment and response to bark
beetle outbreaks in the rocky mountain area. Report to
Congress from Forest Health Protection Washington
B
Office, Forest Service, U.S. Department of Agriculture.
USDA Forest Service, Rocky Mountain Research ­Station,
General Technical Report RMRS-GTR-62
Seybold SJ, Bohlmann J, Raffa KF (2000) Biosynthesis of
coniferophagous bark beetle pheromones and conifer
isoprenoids: evolutionary perspective and synthesis.
Can Entomol 132:697–753
Wood SL (1982) The bark and ambrosia beetles of North and
Central America (Coleoptera: Scolytidae), a taxonomic
monograph. Great Basin Naturalist Memoirs, Number 6
Brigham Young University Provo, UT, 1359 pp
Bark-Gnawing Beetles
Members of the family Togossitidae (order
Coleoptera).
 Beetles
Bark-Lice, Book-Lice or Psocids
(Psocoptera)
arturo baz
Universidad de Alcalá, MadridSpain
The insects of the order Psocoptera (=Copeognatha, Corrodentia) are commonly called psocids,
although outdoor species living on tree trunks and
branches have been called bark-lice, whereas
indoor species, sometimes found in old books,
have been called book-lice. The Psocoptera are a
small order of paraneopteran insects (near 4,000
species have been described around the world)
which are found in a wide range of terrestrial ecosystems throughout the world. Most psocids
inhabit trees and shrubs, some others occur in
ground litter, others are found on rocks and in the
nests of birds and mammals. Some live on herbs
and grasses, and a few in moss, whereas others are
found in caves. Lastly, several species are found in
domestic habitats. The Psocoptera share certain
morphological features with the lice (orders Mallophaga and Siphunculata; Phthiraptera of some
authors), and these taxa are grouped together in
the superorder Psocodea by some authors. Fossil
insects identified as psocids have been reported
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