European spruce bark beetle
Encyclopedia
The European spruce bark beetle (Ips typographus), is a beetle
in the family Scolytidae of European origin. Originally ranging from Europe to Asia Minor
and some parts of Africa, it was introduced to areas such as Norway Spruce forests via imported solid wood packing material, and has been expanding its range throughout the northern spruce
forests.
declivity is slightly shiny, with 4 teeth on each margin side. The third tooth is the biggest and club like on its top. The egg is yellowish-white. The larva
is white and legless. The pupa
is also white.
s are so named because they reproduce in the inner bark, living and dead phloem
tissues, of trees. Adult beetles hibernate in forest litter and host trees when environmental conditions are not favorable for reproduction. When conditions are right, they travel miles in search of a vulnerable host. Once the host is located, the adult burrows through the weakened bark
in order to build tunnels where they can mate and lay eggs. They release pheromones to attract more individuals to the host tree. Two to five weeks after contamination, they may migrate to another host and repeat the process. Once the larvae hatch, they feed and pupate under the bark. Each year, up to three generations may be produced.
Bark beetles communicate with one another using semiochemical
s, a chemical substance or mixture that carries a message. Some electrophysiological
and behavioral statistics show that bark beetles can not only sense olfactory
signals directly from other bark beetles, but also a subset of the angiosperm semiochemical
s from trees not yet deflated by the prey of the clerids
.
It is also possible that beetles are attracted to the pheromone Ipslure
. They are also thought to be attracted to ethanol
, one of the by-products of microbial growth in dead woody tissues.
Bark beetles can form a symbiotic relationship
with certain Ophiostomatales fungi
. These beetles feed on and keep fungal "gardens". The relationship between the ambrosia bark beetles
and spruce beetles is symbiotic and the ambrosia bark beetles
can indirectly feed from many more tree species than those who do not farm fungi
. They allow the fungi to do most of the work in overcoming the tree's chemical defenses before invading the tree. The beetles will then carry the fungal spore
s in structures called mycangia
, which are adapted for transport of symbiotic
fungi from tree to tree.
may have contributed to their invasion of northern European Spruce forests, which is another name for Norway Spruce forests. Movements like this can happen when various environmental factors such as severe storms, drought
, or mass fungal infections damage or kill host trees. Trees in the genera Picea
(spruce), Abies
(fir), Pinus
(pine), and Larix
(larch) are the bark beetles trees of choice. The most recent spruce bark beetle invasive outbreaks are found mainly in fallen, diseased or damaged Norway Spruce. Healthy trees use defenses by producing resin
or latex
, which might contain several insecticidal and fungicidal compounds that kill or injure attacking insects. However, under outbreak conditions, the beetles can overwhelm the tree's defenses.
The invasive European spruce bark beetles attack the Norway spruce. However, they cannot be found in all regions where the Norway Spruce is found. Some scientists hypothesize that the beetles may not be capable of enormous success in the Northern-most reaches of the spruce forests. This is probably due to inadequate climatic oscillations. Other researchers argue that the beetle populations that have evolved in such regions have an active, directed host searching ability, are not equipped for high-dispersal ability.
. Others argue that they cannot be a keystone species
because they are invasive
to the area. However, Muller et al. defines them as such, based on the fact that they have an unusually high number of relationships with other organisms in the surrounding community. Also, they can be considered a keystone species
by virtue of how drastically they can change their environment.
Outbreak species, in general, assist in the renewal of the forest. Spruce beetles are detritivore
s. They feed on and break down dead plant matter, returning essential nutrients to the ecosystem. Also, they further the evolution of stronger, more resistant trees by instigating a range of adaptations to ward off their attacks.
s can be transmitted to conifer spruce by the invasive beetles. One of the most damaging is known as blue stain fungus
, Ophiostoma polonicum Sium. This fungus is capable of destroying healthy trees by hindering the upward flow of water, wilting its foliage
. It also stains the wood with blue streaks, which destroys its commercial value. The results of such beetle outbreaks could be devastating for the lumber industry
in that area because of the amount of time required for natural regression to take place. When this cycle affects the lumber industries by attacking spruce tree farms, they become known as serious pests.
activity. Other common ways that infection can be detected is the presence of red-brown dust in bark crevices, many round exit holes, or small pitch tubes extruding from the bark. Large populations can be detected from a distance by one or many red-topped areas.
in Czech Republic
's Bohemian Forest
. Some groups of experts demand that nature be left alone and outbreaks be allowed to run their course; even at the expense of most of the forest. Others, such as the lumber industry, demand intervention. Some experts argue that salvage logging
tends to have a greater negative effect on the vegetation than the bark beetle outbreak alone. The results found by Magda Jonášová and Karel Prach comparing the effect of forestry intervention on changes in the herb and moss layers of mountain spruce forests after an extensive bark beetle outbreak to letting the forest revive itself show that if the spruce forests were left alone after a bark beetle outbreak, the ecosystem would most likely avoid a pioneer stage and recovery of the forests would be possible. Salvage logging
also had negative effects on the composition of species of the spruce forests, delayed the overall forest recovery. The forest that was studied was the in the Šumava National Park
in Czech Republic, Central Europe in the 1990s. This park is made up of coniferous forests, which are sensitive to both natural and human-made disturbances. However, they can usually easily regenerate after natural disturbances, which are even often needed for persistence of the health of the forests.
e are found. Another method is called clear-cutting
. Infested and surrounding at-risk trees are removed two to three weeks after the first beetle bore into the trees so as to remove the adult beetles as well. Pheromone
traps are yet another proposal: one trap per four hectare
in slightly infested stands, one-two groups of two-three traps per hectare
in moderately infested stands, and three-four groups of four-six traps per hectare in heavily infested stands. In healthy stands, a distance from the trap and the nearest trees should be a minimum of fifteen meters in lowlands and thirty meters in the mountains. Trap trees baited with pheromone
s can then be sprayed with insecticide
, or chemical treatment of emerging beetles are two other options. Removal of all potential breeding material, which include logs with bark, weakened trees, and wind throws, from the forest in the period from October to April may help prevent outbreaks. However, further studies need to be conducted in order to support this particular proposal.
Beetle
Coleoptera is an order of insects commonly called beetles. The word "coleoptera" is from the Greek , koleos, "sheath"; and , pteron, "wing", thus "sheathed wing". Coleoptera contains more species than any other order, constituting almost 25% of all known life-forms...
in the family Scolytidae of European origin. Originally ranging from Europe to Asia Minor
Anatolia
Anatolia is a geographic and historical term denoting the westernmost protrusion of Asia, comprising the majority of the Republic of Turkey...
and some parts of Africa, it was introduced to areas such as Norway Spruce forests via imported solid wood packing material, and has been expanding its range throughout the northern spruce
Spruce
A spruce is a tree of the genus Picea , a genus of about 35 species of coniferous evergreen trees in the Family Pinaceae, found in the northern temperate and boreal regions of the earth. Spruces are large trees, from tall when mature, and can be distinguished by their whorled branches and conical...
forests.
Morphology
Adults are usually 4–5.5 mm (0.15748031496063–0.216535433070866 ) long, cylindrical and robust, black or brownish-black. ElytralElytron
An elytron is a modified, hardened forewing of certain insect orders, notably beetles and a few of the true bugs ; in most true bugs, the forewings are instead called hemelytra, as only the basal half is thickened while the apex is membranous...
declivity is slightly shiny, with 4 teeth on each margin side. The third tooth is the biggest and club like on its top. The egg is yellowish-white. The larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
is white and legless. The pupa
Pupa
A pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...
is also white.
Life cycle and interactions
Bark beetleBark beetle
A bark beetle is one of approximately 220 genera with 6,000 species of beetles in the subfamily Scolytinae. Traditionally, this was considered a distinct family Scolytidae, but now it is understood that bark beetles are in fact very specialized members of the "true weevil" family...
s are so named because they reproduce in the inner bark, living and dead phloem
Phloem
In vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...
tissues, of trees. Adult beetles hibernate in forest litter and host trees when environmental conditions are not favorable for reproduction. When conditions are right, they travel miles in search of a vulnerable host. Once the host is located, the adult burrows through the weakened bark
Bark
Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines and shrubs. Bark refers to all the tissues outside of the vascular cambium and is a nontechnical term. It overlays the wood and consists of the inner bark and the outer bark. The inner...
in order to build tunnels where they can mate and lay eggs. They release pheromones to attract more individuals to the host tree. Two to five weeks after contamination, they may migrate to another host and repeat the process. Once the larvae hatch, they feed and pupate under the bark. Each year, up to three generations may be produced.
Bark beetles communicate with one another using semiochemical
Semiochemical
A semiochemical is a generic term used for a chemical substance or mixture that carries a message. These chemicals acts as messengers within or between species...
s, a chemical substance or mixture that carries a message. Some electrophysiological
Electrophysiology
Electrophysiology is the study of the electrical properties of biological cells and tissues. It involves measurements of voltage change or electric current on a wide variety of scales from single ion channel proteins to whole organs like the heart...
and behavioral statistics show that bark beetles can not only sense olfactory
Olfaction
Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates...
signals directly from other bark beetles, but also a subset of the angiosperm semiochemical
Semiochemical
A semiochemical is a generic term used for a chemical substance or mixture that carries a message. These chemicals acts as messengers within or between species...
s from trees not yet deflated by the prey of the clerids
Cleridae
Cleridae are a family of beetles of the superfamily Cleroidea. They are commonly known as checkered beetles. The Cleridae family has a worldwide distribution, and a variety of habitats and feeding preferences....
.
It is also possible that beetles are attracted to the pheromone Ipslure
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
. They are also thought to be attracted to ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
, one of the by-products of microbial growth in dead woody tissues.
Bark beetles can form a symbiotic relationship
Symbiosis
Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...
with certain Ophiostomatales fungi
Ophiostomatales
The Ophiostomatales are an order of fungi within the class Sordariomycetes....
. These beetles feed on and keep fungal "gardens". The relationship between the ambrosia bark beetles
Ambrosia beetle
Ambrosia beetles are beetles of the weevil subfamilies Scolytinae and Platypodinae , which live in nutritional symbiosis with ambrosia fungi and probably with bacteria...
and spruce beetles is symbiotic and the ambrosia bark beetles
Ambrosia beetle
Ambrosia beetles are beetles of the weevil subfamilies Scolytinae and Platypodinae , which live in nutritional symbiosis with ambrosia fungi and probably with bacteria...
can indirectly feed from many more tree species than those who do not farm fungi
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
. They allow the fungi to do most of the work in overcoming the tree's chemical defenses before invading the tree. The beetles will then carry the fungal spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s in structures called mycangia
Mycangium
The 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...
, which are adapted for transport of symbiotic
Symbiosis
Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...
fungi from tree to tree.
Dispersal ability
European bark beetles have the ability to spread quickly over large areas. Some scientists hypothesize that long-distance movements originating from the Iberian PeninsulaIberian Peninsula
The Iberian Peninsula , sometimes called Iberia, is located in the extreme southwest of Europe and includes the modern-day sovereign states of Spain, Portugal and Andorra, as well as the British Overseas Territory of Gibraltar...
may have contributed to their invasion of northern European Spruce forests, which is another name for Norway Spruce forests. Movements like this can happen when various environmental factors such as severe storms, drought
Drought
A 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...
, or mass fungal infections damage or kill host trees. Trees in the genera Picea
Spruce
A spruce is a tree of the genus Picea , a genus of about 35 species of coniferous evergreen trees in the Family Pinaceae, found in the northern temperate and boreal regions of the earth. Spruces are large trees, from tall when mature, and can be distinguished by their whorled branches and conical...
(spruce), Abies
Fir
Firs are a genus of 48–55 species of evergreen conifers in the family Pinaceae. They are found through much of North and Central America, Europe, Asia, and North Africa, occurring in mountains over most of the range...
(fir), Pinus
Pine
Pines are trees in the genus Pinus ,in the family Pinaceae. They make up the monotypic subfamily Pinoideae. There are about 115 species of pine, although different authorities accept between 105 and 125 species.-Etymology:...
(pine), and Larix
Larch
Larches are conifers in the genus Larix, in the family Pinaceae. Growing from 15 to 50m tall, they are native to much of the cooler temperate northern hemisphere, on lowlands in the north and high on mountains further south...
(larch) are the bark beetles trees of choice. The most recent spruce bark beetle invasive outbreaks are found mainly in fallen, diseased or damaged Norway Spruce. Healthy trees use defenses by producing resin
Resin
Resin 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 latex
Latex
Latex 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 might contain several insecticidal and fungicidal compounds that kill or injure attacking insects. However, under outbreak conditions, the beetles can overwhelm the tree's defenses.
The invasive European spruce bark beetles attack the Norway spruce. However, they cannot be found in all regions where the Norway Spruce is found. Some scientists hypothesize that the beetles may not be capable of enormous success in the Northern-most reaches of the spruce forests. This is probably due to inadequate climatic oscillations. Other researchers argue that the beetle populations that have evolved in such regions have an active, directed host searching ability, are not equipped for high-dispersal ability.
Ecological
European spruce beetles have a significant impact on both the ecological and economic environment of Norway Spruce forests. Together with storm events, bark beetle outbreaks are thought by some to be one of the most important natural disturbances in this region. Some scientists consider spruce bark beetles to be a keystone speciesKeystone species
A keystone species is a species that has a disproportionately large effect on its environment relative to its abundance. Such species play a critical role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem and helping to determine the types and...
. Others argue that they cannot be a keystone species
Keystone species
A keystone species is a species that has a disproportionately large effect on its environment relative to its abundance. Such species play a critical role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem and helping to determine the types and...
because they are invasive
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
to the area. However, Muller et al. defines them as such, based on the fact that they have an unusually high number of relationships with other organisms in the surrounding community. Also, they can be considered a keystone species
Keystone species
A keystone species is a species that has a disproportionately large effect on its environment relative to its abundance. Such species play a critical role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem and helping to determine the types and...
by virtue of how drastically they can change their environment.
Outbreak species, in general, assist in the renewal of the forest. Spruce beetles are detritivore
Detritivore
Detritivores, also known as detritophages or detritus feeders or detritus eaters or saprophages, are heterotrophs that obtain nutrients by consuming detritus . By doing so, they contribute to decomposition and the nutrient cycles...
s. They feed on and break down dead plant matter, returning essential nutrients to the ecosystem. Also, they further the evolution of stronger, more resistant trees by instigating a range of adaptations to ward off their attacks.
Economical
The bark beetles of the European Spruce forests are generally associated with various types of fungi, who each have different basic ecological roles. Several fungi pathogenPathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
s can be transmitted to conifer spruce by the invasive beetles. One of the most damaging is known as blue stain fungus
Blue stain fungus
The blue stain fungus, Grosmannia clavigera, is a species of sac fungus. It spreads to Lodgepole pine, Ponderosa pine, Douglas-fir, and Whitebark pine trees from the body and a special structure in the heads of Mountain Pine Beetles...
, Ophiostoma polonicum Sium. This fungus is capable of destroying healthy trees by hindering the upward flow of water, wilting its foliage
Leaf
A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....
. It also stains the wood with blue streaks, which destroys its commercial value. The results of such beetle outbreaks could be devastating for the lumber industry
Logging
Logging is the cutting, skidding, on-site processing, and loading of trees or logs onto trucks.In forestry, the term logging is sometimes used in a narrow sense concerning the logistics of moving wood from the stump to somewhere outside the forest, usually a sawmill or a lumber yard...
in that area because of the amount of time required for natural regression to take place. When this cycle affects the lumber industries by attacking spruce tree farms, they become known as serious pests.
Detection
Spruce beetles usually infest the lower and middle parts of trunks. Trees that have been attacked are easy to recognize by concentrations of brown dust from bark at the basal areas of stems and trunks. However, sometimes apparently infected trees with green crowns can be without bark because of larval and woodpeckerWoodpecker
Woodpeckers are near passerine birds of the order Piciformes. They are one subfamily in the family Picidae, which also includes the piculets and wrynecks. They are found worldwide and include about 180 species....
activity. Other common ways that infection can be detected is the presence of red-brown dust in bark crevices, many round exit holes, or small pitch tubes extruding from the bark. Large populations can be detected from a distance by one or many red-topped areas.
Conservation
The way in which beetle outbreaks should be dealt with have become heated political debates in locations such as the Sumava National ParkŠumava National Park
Šumava National Park is a National Park in the Plzeň and South Bohemian Regions of the Czech Republic along the border with Germany and Austria...
in Czech Republic
Czech Republic
The 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 Forest
Bohemian Forest
The 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...
. Some groups of experts demand that nature be left alone and outbreaks be allowed to run their course; even at the expense of most of the forest. Others, such as the lumber industry, demand intervention. Some experts argue that salvage logging
Salvage logging
Salvage logging is the practice of logging trees in forest areas that have been damaged by wildfire, flood, severe wind, disease, insect infestation, or other natural disturbance.The primary motivation of salvage logging is economic...
tends to have a greater negative effect on the vegetation than the bark beetle outbreak alone. The results found by Magda Jonášová and Karel Prach comparing the effect of forestry intervention on changes in the herb and moss layers of mountain spruce forests after an extensive bark beetle outbreak to letting the forest revive itself show that if the spruce forests were left alone after a bark beetle outbreak, the ecosystem would most likely avoid a pioneer stage and recovery of the forests would be possible. Salvage logging
Salvage logging
Salvage logging is the practice of logging trees in forest areas that have been damaged by wildfire, flood, severe wind, disease, insect infestation, or other natural disturbance.The primary motivation of salvage logging is economic...
also had negative effects on the composition of species of the spruce forests, delayed the overall forest recovery. The forest that was studied was the in the Šumava National Park
Šumava National Park
Šumava National Park is a National Park in the Plzeň and South Bohemian Regions of the Czech Republic along the border with Germany and Austria...
in Czech Republic, Central Europe in the 1990s. This park is made up of coniferous forests, which are sensitive to both natural and human-made disturbances. However, they can usually easily regenerate after natural disturbances, which are even often needed for persistence of the health of the forests.
Prevention and control methods
Several methods have been proposed to prevent the start of beetle outbreaks. Some suggest using “trap trees” at the beginning of each reproductive cycle. This should be done in March, May, and in late June or early July. The trap trees should be debarked when distinct larval galleries with small larvaLarva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e are found. Another method is called clear-cutting
Clearcutting
Clearcutting, or clearfelling, is a controversial forestry/logging practice in which most or all trees in an area are uniformly cut down. Clearcutting, along with shelterwood and seed tree harvests, is used by foresters to create certain types of forest ecosystems and to promote select species that...
. Infested and surrounding at-risk trees are removed two to three weeks after the first beetle bore into the trees so as to remove the adult beetles as well. Pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
traps are yet another proposal: one trap per four hectare
Hectare
The hectare is a metric unit of area defined as 10,000 square metres , and primarily used in the measurement of land. In 1795, when the metric system was introduced, the are was defined as being 100 square metres and the hectare was thus 100 ares or 1/100 km2...
in slightly infested stands, one-two groups of two-three traps per hectare
Hectare
The hectare is a metric unit of area defined as 10,000 square metres , and primarily used in the measurement of land. In 1795, when the metric system was introduced, the are was defined as being 100 square metres and the hectare was thus 100 ares or 1/100 km2...
in moderately infested stands, and three-four groups of four-six traps per hectare in heavily infested stands. In healthy stands, a distance from the trap and the nearest trees should be a minimum of fifteen meters in lowlands and thirty meters in the mountains. Trap trees baited with pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
s can then be sprayed with insecticide
Insecticide
An insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
, or chemical treatment of emerging beetles are two other options. Removal of all potential breeding material, which include logs with bark, weakened trees, and wind throws, from the forest in the period from October to April may help prevent outbreaks. However, further studies need to be conducted in order to support this particular proposal.
External links
- Species Profile- European Spruce Bark Beetle (Ips typographus), National Invasive Species Information Center, United States National Agricultural LibraryUnited States National Agricultural LibraryThe United States National Agricultural Library is one of the world's largest agricultural research libraries, and serves as a National Library of the United States and as the library of the United States Department of Agriculture...
. Lists general information and resources for European Spruce Bark Beetle.