| European spruce bark beetle | |
|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Coleoptera |
| Family: | Scolytidae |
| Genus: | Ips |
| Species: | I. typographus |
| Binomial name | |
| Ips typographus (Linnaeus, 1758) |
|
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,[1] and has been expanding its range throughout the northern spruce forests.
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Adults are usually 4.0–5.5 millimetres (0.16–0.22 in) long, cylindrical and robust, black or brownish-black. Elytral 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.
Bark beetles are so named because they reproduce in the inner bark, living and dead phloem tissues, of trees.[2] 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.[3] 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 semiochemicals, a chemical substance or mixture that carries a message.[4] 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 semiochemicals 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.[2]
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 spores in structures called mycangia, which are adapted for transport of symbiotic fungi from tree to tree.[5]
European bark beetles have the ability to spread quickly over large areas. Some scientists hypothesize that long-distance movements originating from the Iberian Peninsula may have contributed to their invasion of northern European Spruce forests, which is another name for Norway Spruce forests.[6] 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.[7] However, under outbreak conditions, the beetles can overwhelm the tree's defenses.[7]
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.[8] 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.[8]
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.[7] Some scientists consider spruce bark beetles to be a keystone species.[3] 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.[3]
Outbreak species, in general, assist in the renewal of the forest. Spruce beetles are detritivores. 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.
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 pathogens 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.[2] 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.[7] When this cycle affects the lumber industries by attacking spruce tree farms, they become known as serious pests.[1]
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 woodpecker 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.[9]
The way in which beetle outbreaks should be dealt with have become heated political debates in locations such as the Sumava National Park 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.[3] 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.[10] 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.
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 larvae 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 pheromones can then be sprayed with insecticide, or chemical treatment of emerging beetles are two other options.[11] 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.