A
bark beetle is one of approximately 220
generaGenera is a commercial operating system and development environment for Lisp machines developed by Symbolics. It is essentially a fork of an earlier operating system originating on the MIT AI Lab's Lisp machines which Symbolics had used in common with LMI and Texas Instruments...
with 6,000
speciesIn biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of beetles in the subfamily
Scolytinae. Traditionally, this was considered a distinct
familyIn biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Scolytidae, but now it is understood that bark beetles are in fact very specialized members of the "true
weevilA weevil is any beetle from the Curculionoidea superfamily. They are usually small, less than , and herbivorous. There are over 60,000 species in several families, mostly in the family Curculionidae...
" family (
CurculionidaeCurculionidae is the family of the "true" weevils . It was formerly recognized in 1998 as the largest of any animal family, with over 40,000 species described worldwide at that time...
). Well-known species are members of the
type genusIn biological classification, a type genus is a representative genus, as with regard to a biological family. The term and concept is used much more often and much more formally in zoology than it is in botany, and the definition is dependent on the nomenclatural Code that applies:* In zoological...
ScolytusScolytus is a genus of bark beetles . It includes several species notorious for destroying trees in the forests. The Dutch elm disease is spread in North America by two species : the native elm bark beetle, Hylurgopinus rufipes, and the European elm bark beetle, Scolytus multistriatus...
- namely the
European elm bark beetleDutch elm disease is a disease caused by a member of the sac fungi category, affecting elm trees which is spread by the elm bark beetle. Although believed to be originally native to Asia, the disease has been accidentally introduced into America and Europe, where it has devastated native...
S. multistriatus and the large elm bark beetle
S. scolytus, which like the American elm bark beetle
Hylurgopinus rufipes, transmit
Dutch elm diseaseDutch elm disease is a disease caused by a member of the sac fungi category, affecting elm trees which is spread by the elm bark beetle. Although believed to be originally native to Asia, the disease has been accidentally introduced into America and Europe, where it has devastated native...
fungi (
Ophiostoma). The
mountain pine beetleThe mountain pine beetle Dendroctonus ponderosae, is a species of bark beetle native to the forests of western North America from Mexico to central British Columbia. It has a hard black exoskeleton, and measures about 5 millimeters, about the size of a grain of rice.Mountain pine beetles inhabit...
Dendroctonus ponderosae, southern pine beetle
Dendroctonus frontalisDendroctonus frontalis, the southern pine beetle, is a species of bark beetle native to the forests of southern United States, Mexico and Central America. It has a hard reddish brown to black exoskeleton and measures approximately , about the size of a grain of rice...
and their near relatives are major pests of conifer forests in North America. A similarly aggressive species in Europe is the spruce Ips
Ips typographus. A tiny bark beetle—the coffee berry borer,
Hypothenemus hampei is a major pest of coffee around the world.
Ecology
Bark beetles are so-named because the best known species reproduce in the inner bark (living and dead phloem tissues) of
treeA tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...
s. Some species, such as the
mountain pine beetleThe mountain pine beetle Dendroctonus ponderosae, is a species of bark beetle native to the forests of western North America from Mexico to central British Columbia. It has a hard black exoskeleton, and measures about 5 millimeters, about the size of a grain of rice.Mountain pine beetles inhabit...
(
Dendroctonus ponderosae), attack and kill live trees. Most, however, live in dead, weakened, or dying hosts. Bark beetles are ecologically and economically significant. Outbreak species help to renew the forest by killing older trees. Other species aid in the decomposition of dead wood. However, several outbreak-prone species are known as notorious pests.
Bark beetles often attack trees that are already weakened by
diseaseA disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
,
droughtA drought is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region...
,
smogSmog is a type of air pollution; the word "smog" is a portmanteau of smoke and fog. Modern smog is a type of air pollution derived from vehicular emission from internal combustion engines and industrial fumes that react in the atmosphere with sunlight to form secondary pollutants that also combine...
, conspecific beetles or physical damage. Healthy trees may put up defenses by producing
resinResin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...
or
latexLatex is the stable dispersion of polymer microparticles in an aqueous medium. Latexes may be natural or synthetic.Latex as found in nature is a milky fluid found in 10% of all flowering plants . It is a complex emulsion consisting of proteins, alkaloids, starches, sugars, oils, tannins, resins,...
, which may contain a number of insecticidal and fungicidal compounds that can kill or injure attacking insects, or simply immobilize and suffocate them with the sticky fluid. Under outbreak conditions, the sheer number of beetles can, however, overwhelm the tree's defenses, and the results can be disastrous for the lumber industry.
In some places, such as the Šumava National Park in the
Czech RepublicThe Czech Republic is a landlocked country in Central Europe. The country is bordered by Poland to the northeast, Slovakia to the east, Austria to the south, and Germany to the west and northwest....
's
Bohemian forestThe Bohemian Forest, also known in Czech as Šumava , is a low mountain range in Central Europe. Geographically, the mountains extend from South Bohemia in the Czech Republic to Austria and Bavaria in Germany...
, problems with bark beetles have become a heated issue with a political dimension. On one side, some experts (usually with a background in
environmental scienceEnvironmental science is an interdisciplinary academic field that integrates physical and biological sciences, to the study of the environment, and the solution of environmental problems...
s) demanded that nature be left alone and that natural processes be allowed to take their course, even if it meant the bark beetle would destroy most of the forest. On the other side, other experts (usually with a background in
forest management200px|thumb|right|[[Sustainable development|Sustainable]] forest management carried out by [[Complejo Forestal y Maderero Panguipulli|Complejo Panguipulli]] has contributed to the preservation of the forested landscape around [[Neltume]], a sawmill town in Chile...
) demanded intervention. During the 1980s and 1990s, the Šumava park management mostly favored intervention. Many outside groups became involved in the dispute, such as the lumber industry (which supported intervention because of possible profit to be made), or some local politicians, afraid that tourists would turn back from a forest decayed after a beetle invasion. The anti-intervention side got support from entomologists from the
Czech Academy of SciencesThe Academy of Sciences of the Czech Republic was established in 1992 by the Czech National Council as the Czech successor of the former Czechoslovak Academy of Sciences. The Academy is the leading non-university public research institution in the Czech Republic...
and from several
environmental organizationAn environmental organization is an organization that seeks to protect, analyze or monitor the environment against misuse or degradation or lobby for these goals....
s, such as
Friends of the EarthFriends of the Earth International is an international network of environmental organizations in 76 countries.FOEI is assisted by a small secretariat which provides support for the network and its agreed major campaigns...
. At the height of the dispute, there were cases where activists literally defended the trees with their bodies, tying themselves to the trunks, and the dispute was widely covered in the main Czech daily newspapers and on TV news.
Some bark beetles form a symbiotic relationship with certain
OphiostomatalesThe Ophiostomatales are an order of fungi within the class Sordariomycetes....
fungi, and are named "
ambrosia beetleAmbrosia beetles are beetles of the weevil subfamilies Scolytinae and Platypodinae , which live in nutritional symbiosis with ambrosia fungi and probably with bacteria...
s" after these "
ambrosia fungiAmbrosia fungi are fungal symbionts of ambrosia beetles.There are a few dozen described ambrosia fungi, currently placed in polyphyletic genera Ambrosiella, Rafaellea and Dryadomyces . Probably many more species remain to be discovered...
". The ambrosia beetles (such as
Xyleborus) feed on fungal "gardens" and are one of only three insect groups known to farm fungi. The other two groups are ants and
termiteTermites are a group of eusocial insects that, until recently, were classified at the taxonomic rank of order Isoptera , but are now accepted as the epifamily Termitoidae, of the cockroach order Blattodea...
s, neither of which is particularly closely related to beetles. Courtesy of the fungus, ambrosia bark beetles are able to indirectly feed from many more species of trees than their evolutionary relatives that do not feed on fungi, by having the fungi do the work of overcoming the plants' chemical defenses. The beetles carry the fungal spores in special structures, called
mycangiaThe term mycangium is used in biology for special structures on the body of an animal that are adapted for the transport of symbiotic fungi . This is seen in many xylophagous insects , which apparently derive much of their nutrition from the digestion of various fungi that are growing amidst the...
, and inoculate the trees as they attack them.
Like many other insects, Scolytinae will emit pheromones to attract conspecifics which are thus drawn to trees already colonized by bark beetles. This can result in heavy infestations and eventually death of the tree. Many are also attracted to ethanol, one of the byproducts of microbial growth in dead woody tissues.
External links and further reading
on the
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/
IFASThe University of Florida’s Institute of Food and Agricultural Sciences is a federal-state-county partnership dedicated to developing knowledge in agriculture, human and natural resources, and the life sciences, and enhancing and sustaining the quality of human life by making that information...
Featured Creatures Web site
- Nordhaus, Hannah. Bark Beetle Outbreaks in Western North America: Causes and Consequences. University of Utah Press: Salt Lake City, 2009. ISBN 978-0-87480-965-7