| Xyleborus dispar | |
|---|---|
 | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Coleoptera |
| Infraorder: | Cucujiformia |
| Family: | Curculionidae |
| Genus: | Xyleborus |
| Species: | X. dispar |
| Binomial name | |
| Xyleborus dispar (Fabricius), 1792 | |
Xyleborus dispar is a species of bark beetle commonly called the Pear blight beetle, or the European shothole borer. It is an invasive species in North America, and can be a pest in orchards and forests throughout its range.
Xyleborus dispar was first described by Fabricius in 1792 as Apate dispar. Current status was given in 1992 by Wood & Bright. [1] North American beetles were once believed to be a separate species, but are now recognized as an invasive branch of the European species. [2] [3] [4] It was named after the similarity of the beetle’s effect on trees to the pear blight fungus. [3]
The body is wide and stout, and black-brown with a cylindrical shape. The legs and antennae are reduced to facilitate movement through tunnels. The female is 3.2-3.7 mm long, and is elongated and cylindrical compared with the smaller male (1.8-2.1 mm long). [2] The females are about twice as long as wide. The elytra are dark in color with longitudinal streaks. The eggs are oval-shaped (1mm x 0.06mm) and white. [5] [6]
It is native to temperate and boreal regions of Europe and Asia. It has been introduced to North America prior to 1817, [7] and is known to be present in the eastern United States from the Great Lakes states south to North Carolina, and the Pacific Northwest, suggesting that two separate introduction events occurred. [2] [4]
This beetle usually attacks compromised trees, however in its exotic range or when populations are especially high it has been known to infest healthy trees. [3] [4] The holes that the beetle makes in trees are small in diameter and circular. The holes in trees have a short (1–3 cm) entrance hole leading to a series of transverse tunnels containing eggs and larvae. [6] Each female lays about 50 eggs, and once pupation is complete, the beetles stay in the galleries until the following spring. [5]
The adult is known to overwinter in the holes they have created, and true hibernation occurs. [8] [5] [6] One generation per year is produced. [6] In early spring the female exits the hole and disperses, the male is smaller and wingless and stays in their natal tree. [4] Once a female discovers a suitable tree, she sends out an aggregation hormone that attracts many other beetles, so a tree may have a large infestation, but usually not more than 40 beetles. [4] Beetles may be found into June; the peak of activity is March and early April. [4]
The beetle is strongly polyphagous, and has been known to infest many types of trees over its wide host range. These include Acer, Aesculus, Alnus, Betula, Castanea, Celtis, Crataegus, Corylus, Cydonia, Fagus, Fraxinus, Juglans, Liriodendron, Magnolia, Malus, Platanus, Populus, Prunus, Punica, Pyrus, Quercus, Salix, Styrax, Tilia, Ulmus, and Vitis. [2] [5] [9] [4] This beetle could be able to infect such a wide variety of trees because of its association with fungi potentially overcoming some of the plant’s natural defenses. [10] In the field of forest ecology, ambrosia beetles such as Xyleborus dispar that attack dead or dying plant matter are important for the decay process and leads to nutrient cycling. [11] [6]
Xyleborus dispar is the only species in the tribe Scolytidae to exhibit a true diapause. [6]
Xyleborus dispar forms a symbiotic relationship with the fungus Ambrosiella hartigii. [10] [8] [9] Adults introduce the fungi to their offspring, and it is stored in intersegmental pouches between pro- and mesonotum in the female. [12] [6] Larvae and adults then consume the fungus as it grows on the wood inside the galleries. The fungus often stains sapwood in the areas surrounding the larval galleries. [3] [11]
This species is an invasive species in North America, and though it is already widely dispersed, it has the potential to invade new areas due to inbreeding among galleries enabling a small number of females to colonize new areas. [4] [6] The beetle is mostly an economic pest of fruit trees including apple, [13] pear, [14] apricot, and peach, but damage has also been reported from vineyards. It is a serious pest of Chestnut. [5]
The species can be detected on damaged trees by the presence of sap flows, and sawdust on tree limbs or the ground indicating recent excavations. [5] [11] Drought, waterlogged soils, and temperature damage can make trees more susceptible to Xyleborus dispar infestations. [14] [4] Infested trees experience delayed growth. [4] [5]
Control
Xyleborus dispar, as well as other species of ambrosia beetles, are often attracted by the scent of alcohol traps, due to the fact that stressed trees produce ethanol as a byproduct of microbial growth in the dead woody tissues. [15] [13] Red winged sticky traps or window flight traps baited with ethanol can be an effective control of this species. [15] [5] Synthetic aggregation hormones may also be effective for controlling ambrosia beetles. [11]
It is not known to have a large number of natural enemies, as larvae are typically well-protected in their galleries. [4] [6] No effective method of biological control exists at present, but bacteria found on the adult has been proposed as a means of treatment. [16] [17] Typically pesticides are ineffective due to the protected nature of the galleries, [5] and very direct spraying is needed. Destroying branches on the trees that are affected may be necessary, and is effective at controlling outbreaks. [5]
The Curculionidae are a family of weevils, commonly called snout beetles or true weevils. They are one of the largest animal families with 6,800 genera and 83,000 species described worldwide. They are the sister group to the family Brentidae.
Ambrosia beetles are beetles of the weevil subfamilies Scolytinae and Platypodinae, which live in nutritional symbiosis with ambrosia fungi. The beetles excavate tunnels in dead, stressed, and healthy trees in which they cultivate fungal gardens, their sole source of nutrition. After landing on a suitable tree, an ambrosia beetle excavates a tunnel in which it releases spores of its fungal symbiont. The fungus penetrates the plant's xylem tissue, extracts nutrients from it, and concentrates the nutrients on and near the surface of the beetle gallery. Ambrosia fungi are typically poor wood degraders, and instead utilize less demanding nutrients. Symbiotic fungi produce and detoxify ethanol, which is an attractant for Ambrosia beetles and likely prevents growth of antagonistic pathogens and selects for other beneficial symbionts. The majority of ambrosia beetles colonize xylem of recently dead trees, but some attack stressed trees that are still alive, and a few species attack healthy trees. Species differ in their preference for different parts of trees, different stages of deterioration, and in the shape of their tunnels ("galleries"). However, the majority of ambrosia beetles are not specialized to any taxonomic group of hosts, unlike most phytophagous organisms including the closely related bark beetles. One species of ambrosia beetle, Austroplatypus incompertus exhibits eusociality, one of the few organisms outside of Hymenoptera and Isoptera to do so.
A bark beetle is the common name for the subfamily of beetles Scolytinae. Previously, this was considered a distinct family (Scolytidae), but is now understood to be a specialized clade of the "true weevil" family (Curculionidae). Although the term "bark beetle" refers to the fact that many species feed in the inner bark (phloem) layer of trees, the subfamily also has many species with other lifestyles, including some that bore into wood, feed in fruit and seeds, or tunnel into herbaceous plants. Well-known species are members of the type genus Scolytus, namely the European elm bark beetle S. multistriatus and the large elm bark beetle S. scolytus, which like the American elm bark beetle Hylurgopinus rufipes, transmit Dutch elm disease fungi (Ophiostoma). The mountain pine beetle Dendroctonus ponderosae, southern pine beetle Dendroctonus frontalis, 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 on coffee plantations around the world.
Xyleborus is by far the largest ambrosia beetle genus in the tribe Xyleborini, with over 500 species.
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 wood fibers. In some cases, as in ambrosia beetles, the fungi are the sole food, and the excavations in the wood are simply to make a suitable microenvironment for the fungus to grow. In other cases, wood tissue is the main food, and fungi weaken the defense response from the host plant.
Xyleborus glabratus, the redbay ambrosia beetle, is a type of ambrosia beetle invasive in the United States. It has been documented as the primary vector of Raffaelea lauricola, the fungus that causes laurel wilt, a disease that can kill several North American tree species in the family Lauraceae, including redbay, sassafras, and avocado.
Ips is a genus of beetles in the family Curculionidae, the true weevils. They are bark beetles, members of the subfamily Scolytinae. Species are distributed throughout the Northern Hemisphere. Some are known as introduced species in Australia and Africa. Many species are pests of forest trees, especially pines and spruces. They are known commonly as engraver beetles, ips engraver beetles, and pine engravers.
Euwallacea fornicatus is a species complex consisting of multiple cryptic species of ambrosia beetles, known as an invasive species in California, Israel and South Africa. The species has also been unintentionally introduced into exotic greenhouses in several European countries. As the rest of the ambrosia beetles, E. fornicatus larvae and adults feed on a symbiotic fungus carried in a specific structure called mycangium. In E. fornicatus, the mycangium is located in the mandible. The combination of massive numbers of beetles with the symbiotic fungus kills trees, even though the fungus alone is a weak pathogen.
Xylosandrus compactus is a species of ambrosia beetle. Common names for this beetle include black twig borer, black coffee borer, black coffee twig borer and tea stem borer. The adult beetle is dark brown or black and inconspicuous; it bores into a twig of a host plant and lays its eggs, and the larvae create further tunnels through the plant tissues. These beetles are agricultural pests that damage the shoots of such crops as coffee, tea, cocoa and avocado.
Platypus cylindrus, commonly known as the oak pinhole borer, is a species of ambrosia beetle in the weevil family Scolytinae. The adults and larvae burrow under the bark of mature oak trees. It is native to Europe.
Species which are not native to a forest ecosystem can act as an agent of disturbance, changing forest dynamics as they invade and spread. Invasive insects and pathogens (diseases) are introduced to the United States through international trade, and spread through means of natural and human-dispersal. Invasive insects and pathogens are a serious threat to many forests in the United States and have decimated populations of several tree species, including American chestnut, American elm, eastern hemlock, whitebark pine, and the native ash species. The loss of these tree species is typically rapid with both short and long-term impacts to the forest ecosystem.
Xyloterinus is a genus of typical bark beetles in the family Curculionidae. This is a monotypic genus and the one described species is Xyloterinus politus. It is native to North America where it infests both hardwood and softwood trees, as well as stacks of logs.
Xylosandrus germanus, known generally as the alnus ambrosia beetle or black stem borer, is a species of ambrosia beetle in the family Curculionidae. The black stem borer is native to eastern Asia, but is an invasive species in Europe and North America. This species carries and feeds on associated ambrosia fungus, Ambrosiella grosmanniae.
Platypus quercivorus, the oak ambrosia beetle, is a species of weevil and pest of broad-leaved trees. This species is most commonly known for vectoring the fungus responsible for excessive oak dieback in Japan since the 1980s. It is found in Japan, India, Indonesia, New Guinea, and Taiwan.
Euplatypus parallelus, previously known as Platypus parallelus, is a species of ambrosia beetle in the weevil family Curculionidae. The adults and larvae form galleries in various species of tree and logs. It is native to Central and South America but has spread globally, is present in Africa and is well established in tropical Asia.
Cnestus mutilatus, commonly known as the camphor shot borer, camphor shoot borer, or sweetgum ambrosia beetle, is a species of ambrosia beetle in the subfamily Scolytinae of the weevil family Curculionidae. It is native to Asia, but has been established as an invasive species in the United States since 1999.
Euwallacea interjectus, is a species of weevil native to Asia but introduced to Westerns parts of the world.
Euwallacea perbrevis, commonly known as tea shot-hole borer, is a species of weevil native to South and South-East Asia through to Australia, but introduced to Western countries.
Euwallacea similis, is a species of weevil native in the Oriental region through to Australia but shows a cosmopolitan distribution due to introduction to many parts of the world.
Ambrosiella roeperi is the fungal symbiont of the granulate ambrosia beetle, Xylosandrus crassiusculus, facilitating this insect’s capacity to accumulate on and damage a diverse array of woody plants from around the world. It is one of several important nutritional partners derived from order Microascales that sustain and are transported by xylomycetophagous scolytine beetles.
