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   Dendroctonus valens (insect)
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    Taxonomic name: Dendroctonus valens LeConte, 1860
    Synonyms: Dendroctonus beckeri Thatcher, Dendroctonus rhizophagusThomas & Bright
    Common names: dendroctone rouge de l'epinette, dendroctone rouge de l'épinette (French), hong zhi da xiao du, qiang da xiao du, red turpentine bark beetle, red turpentine beetle
    Organism type: insect
    Timber imports into China in the 1980s probably translocated the North American pest Dendroctonus valens (red turpentine beetle) into the country. It has since established itself vast tracts of ecologically and economically valuable pine forest in northern China, threatening reforestation and forest protection programmes in the country. The Chinese State Forestry Administration ranks the red turpentine bark beetle as the second most important national forest pest.
    Description
    The 1 mm long eggs of Dendroctonus valens are white, shiny and ovoid cylindrical in shape. The grub-like legless larvae are off-white with a brown head capsule and hind end. Small, pale-brown tubercles are evident in rows along each side of the body. The larva grows to a length of up to 12 mm. The pupae are slightly shorter than the larva and white. They develop into a beetle about the size of a grain of rice. At first the beetle is tan and is called a callow adult. It then rapidly darkens to a reddish brown (Smith 1971). The red turpentine beetle's color is similar to that of bark giving it good camouflage (Yan et al. 2005).
    Bark beetles have strong mandibles for chewing; antennae are elbowed with the outer segments enlarged and club-like; when viewed from above, the head is partly or completely hidden by the pronotum (Seybold Paine & Dreistadt 2008). The pronotum is the upper surface of the prothorax; the shape of the pronotum is often important in identification of beetles.
    Identification: Pitch Tubes & Frass (Smith 1971; Randall 2006; Seybold, Paine & Dreistadt 2008): Beetle mining activity produces a mix of resin and sawdust-like frass. This mass of congealed resin oozes out of the boring hole and forms what is known as a pitch tube on the bole of the tree. These are usually found up to a height of two or three meters above the ground. Pitch tubes vary in size, texture and color, depending on the kind of tree and the relative amounts of bark borings and frass embedded in the resin. The resin is usually white to yellow and the borings are red. The pitch tube may vary in colour from white to light pink to reddish brown. The pitch tube may be as large as 5 cm in diameter. On fir or spruce, which produce little resin, pitch tubes are small or absent, but pitch pellets may be found on the ground at the tree base in the form of small white granules. Frass accumulates in bark crevices or drops to the ground or into spider webs. Small emergence holes in bark indicate the possibility of bark beetles. Bark should be removed to inspect signs of dead and degraded inner bark and new adult beetles that have not emerged. Red turpentine beetles usually pack their egg-laying galleries with granular, reddish, pitchy borings or frass (whereas engraver beetles maintain clean open galleries). Galleries vary from 13 mm to 25 mm in diameter and from a few centimeters to a meter or more in length and are generally vertical. Stressed trees often exhibit crown symptoms which are usually the direct result of associated attacks by other bark beetles. Symptoms include: shorter needles, poor needle retention resulting in tufts of foliage, a thin crown, off-color chlorotic foliage fading to yellow or sorrel/copper-red, slow height growth and/or dead or dying branches.
    Similar Species
    Dendroctonus beckeri, Dendroctonus terebrans, Ips emarginatus, Ips mexicanus, Ips paraconfusus, Ips pini, Ips plastographus

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    Occurs in:
    agricultural areas, natural forests, planted forests, ruderal/disturbed, urban areas
    Habitat description
    Dendroctonus valens is found in coniferous and mixed coniferous forests in North and Central America where it colonises stressed pines (Erbilgin Nadir & Raffa 2002; Yan et al. 2005; Cai et al. 2008). It is a common pest of forest and park trees of pole-size or larger; in North America the beetle may attack freshly cut stumps and trees that are injured or weakened by roadbuilding, construction, logging, drought, fire or other insects (Smith 1971).

    The most heavily attacked forests in China are located in mountains ranges in the Shanxi province from 600 to 2000 meters elevation (Zhang et al. 2002, in Yan et al. 2005). P. tabuliformis is a major reforestation species widely planted on degraded land; this increases tree stress and predisposes it to D. valens attack (Li et al. 2001 Yan et al. 2005). Mature and over-mature P. tabuliformis forests are infested, while younger forests are seldom attacked (Miao et al. 2001, in Yan et al. 2005).
    D. valens occurs within a climatic region of China described as “warm temperature semi-moist” (Wu and Feng 1994, in Yan et al. 2005). Precipitation in northern China is generally lower than in other regions, especially from October to May (Sun et al. 2002, Yan et al. 2005), which may create favourable conditions for D. valens. High humidity and consecutive rainfall disrupts the growth of larvae and eggs of D. valens (Miao et al. 2001, in Yan et al. 2005). Parts of Northern China are becoming drier, hotter and plagued by drought leaving the primary pine host P. tabuliformis stressed and contributing to the current outbreak of D. valens (Sun & Shuqing et al. 2002, Li et al. 2001, Miao et al. 2001, in Yan et al. 2005). Winter temperatures, in particular, have been warmer than in previous years and appear to be a critical factor for beetle survival (Xu et al. 1986; Li et al. 2001).

    General impacts
    Bark beetles (family: Scolytidae) are common pests of conifers, especially pine (Seybold Paine & Dreistadt 2008). The red turpentine beetle has been recorded on at least 40 species of conifer (Liu et al. 2006). Dendroctonus valens has a high intrinsic capacity for adaptation with new hosts compared to other species of Dendroctonus (Sturgeon & Mitton 1982, Kelley & Farrell 1998, in Erbilgin et al. 2007).
    D. valens attacks all pine species, and occasionally spruce and larch, within its range in North America (Yan et al. 2005). Major Pinus spp. affected are P. ponderosa, P. contorta, P. jeffreyi, P. lambertiana, P. monticola, P. radiata, P. strobes, P. resinosa, P. rigida, P. echinata and Pinus banksian (Yan et al. 2005). Damage to Pinus armandi and Picea meyeri is unconfirmed (Zhang et al. 2002, in Yan et al. 2005). P. ponderosa is reported as the tree most frequently infested with D. valens and P. radiata as the tree most frequently killed by D. valens infestations (Smith 1971). In China D. valens primarily attacks P. tabuliformis and P. bungeana. Occasional hosts include Picea meyeri and P. sylvestris (Yan et al. 2005). P. sylvestris var. mongolica is a rare pine species found in Shanxi province and it has occasionally been attacked by D. valens. The oleoresin compositions of P. massoniana and P. armandi are so similar to P. tabuliformis that they are presumed hosts. However, it is believed that all Asian pine are potentially at risk of D. valens infestation (Yan et al. 2005). In China D. valens will colonise both stressed and healthy pines rather than only stressed pines as is the case in North America. The enormous damage caused D. valens in China is thought to be facilitated by drought conditions, degradation of pine sites, the presence of fungal associates and the use of monocultures (Li et al. 2001, in Yan et al. 2005). Logging and farming activities may also contribute to the spread of the beetle (Furniss & Carolin 1977; Miao et al. 2001).The red turpentine beetle is spreading throughout four Chinese provinces. In these provinces it has infested and killed more than 6 million P. tabulaeformis, covering an area of half a million hectares of ecologically and economically valuable forest (Cognato et al. 2005; Liu & Dai 2006). In northern China the land is very dry, the watershed is low and soil conservation is paramount. Billions of tons of agricultural and other soils are annually washed down the Yellow River. Reforestation and forest protection programs, begun in the 1900s, have since involved the planting of P. tabulaeformis and P. armandi pine to reforest the land and prevent soil erosion. The status of these reforestation programs is currently threatened by D. valens infestations. The potential damage inflicted by D. valens to reforested and naturally forested lands in northern Chinis enormous (LUBIES 2004). The interaction between D. valens and native pine-infesting diseases, beetles and insects (including two congeners D. Kugelann and D. armandi) is unknown (Yan et al. 2005). Secondary bark beetles such as D. valens may vector root disease organisms (Joseph et al. 2001). In the United States D. valens is known to carry the virulent fungus Leptographium terebrantis which infects ponderosa pine and may contribute to host pine mortality (LUBIES 2004; Yan et al. 2005). It is unknown what fungal species may be associated with D. valens in its range in China.
    Notes
    In parts of China where temperatures reach below -18 degrees C Dendroctonus valens may survive over-winter in pine roots (but not tree boles) (Wu et al. 2002, in Yan et al. 2005); this may be an important survival strategy of the beetle in Chinese forests (Miao et al. 2001, Wu et al. 2002, in Yan et al. 2005).
    Geographical range
    Native range: Dendroctonus valens is the most widely distributed pine bark beetle in North America (Owen 2003, in Liu et al. 2006). Except for the southern Atlantic Coast and Gulf Coast States, D. valens is common in pine and mixed conifer forests of the northeastern and western United States, southern Canada (Nova Scotia), Mexico and Honduras (Bright 1976, in Yan et al. 2005; Cognato 2003; Wood 1982b, in Erbilgin et al. 2007). Its native range extends roughly from 15 degrees N to 60 degrees N latitude, but it is concentrated between 30 degrees N to 50 degrees N (Wood 1963, 1982, Bright 1976, in Yan et al. 2005). It's range may extend farther north in Canada and into Alaska and there is one record of its occurrence in Guatemala (Smith 1971).
    Known introduced range: In China D. valens is widely distributed in Shanxi province and parts of the adjacent provinces of Hebei, Henan, and Shaanxi. The most heavily attacked forests are located in the Taihang, Lulang, and Zhongtiao Mountains in Shanxi province 35 degrees N to 39 degrees N latitude, from 600 to 2000 meters elevation (Zhang et al. 2002, in Yan et al. 2005).
    Potential Range: Considering its wide host range and geographic distribution in North America and the abundance of suitable pine hosts throughout Eurasia (Critchfield and Little 1966, in Erbilgin et al. 2007), the distribution of D. valens in the Palearctic region are expected to increase. (The Palearctic ecoregion consists of Europe, North Africa, northern parts of the Arabian Peninsula and parts of Asia north of the Himalaya foothills and not including Southeast Asia or the Indian subcontinent.) In China D. valens has many potential new pine hosts which may provide a continuous corridor for its spread from its region of introduction in northeastern China across Eurasia to Europe (Critchfield and Little 1966, in Erbilgin et al. 2007). Because pines are a major reforestation species in China and P. tabuliformis is widely planted across a large portion of the country, the potential range of D. valens is nationwide (Britton & Sun 2002, in Yan et al. 2005).
    Introduction pathways to new locations
    Forestry: The quantity of imported timber is increasing rapidly with the economic development of China. Longicorn beetles, bark beetles and termites are important timber pests that may be introduced by importing timber. These organisms are a considerable threat to Chinese forestry (Liu & Dai 2006). Bark-covered conifer logs shipped from the western US to Shanxi during the 1980s are thought to be origin of the current infestation of the red turpentine beetle in China (Cai et al. 2008).
    Natural dispersal: D. valens is capable of flying long distances. It spread rapidly from Shanxi province to three other adjacent provinces (Hebei, Henan, and Shaanxi) (Yan et al. 2005). The flight distance of D. valens in the United States of America can exceed 16 km. In China flight distances of up to 35 km have been documented (Smith 1971, Zhang et al. 2002, in Yan et al. 2005).
    People sharing resources:
    Seafreight (container/bulk):
    Solid wood packing material: Bark beetles (Coleoptera: Scolytidae) are particularly liable to bypass quarantine undetected in wood articles (Smith 1971). Bark beetles are most often intercepted in dunnage and solid wood packing material at US ports of entry (Haack 2001, in Cognato et al. 2005).
    Transportation of habitat material: Humans facilitate the spread of D. valens between otherwise widely separated pine strands. Pine material with intact bark may harbor D. valens. The harvesting of dying, infested trees and logs facilitates D. valens spread through China (Yan et al. 2005). Such materials are considered to be high risk goods as they are suitable habitat material for D. valens. The harvesting of pine trees and logs is considered to be a high risk activity (Yan et al. 2005).


    Local dispersal methods
    Forestry (local):
    Natural dispersal (local): D. valens is capable of flying long distances. It spread rapidly from Shanxi province to three other adjacent provinces (Hebei, Henan, and Shaanxi) (Yan et al. 2005). The flight distance of D. valens in the United States of America can exceed 16 km. In China flight distances of up to 35 km have been documented (Smith 1971, Zhang et al. 2002, in Yan et al. 2005).
    People sharing resources (local): The principle means of spread of D. valens in areas where pine stands are widely separated appears to be spread by humans. Any pine material with intact bark is considered to be high risk goods as it is suitable habitat material for D. valens. Harvesting of pine trees and logs is a high risk activity in terms of facilitating D. valens spread (Yan et al. 2005).
    Transportation of habitat material (local): The principle means of spread of D. valens in areas where pine stands are widely separated appears to be spread by humans. Any pine material with intact bark is considered to be high risk goods as it is suitable habitat material for D. valens. Harvesting of pine trees and logs is a high risk activity in terms of facilitating D. valens spread (Yan et al. 2005).
    Management information
    Preventative measures: Quarantine restrictions in northern China prevent the unauthorised movement of infested material including trees, logs and wood products (Yan et al. 2005). Cargo is currently checked by hand. To avoid over-sights improved equipment and methods are needed (Yang 1993, in Liu & Dai 2006).
    Pine plots in China are inspected in the summer and the fall for indicators of D. valens attack, such as the presence of pitch tubes or boring material (Yan et al. 2005). Flight traps, funnel traps and pitfall traps are all used to monitor beetle numbers (Erbilgin Nadir & Raffa 2002). Lower stem flight traps have been shown to catch relatively high numbers of D. valens (Yan et al. 2005).

    Chemical: Bark beetles are good candidates for semiochemical-based control methods (Borden 1997, in Rappaport Owen & Stein 2001). The use of ecologically-selective semiochemicals are environmentally friendly and non-toxic (Carmona Undated). Research on bark beetle response to pine host volatiles and beetle pheromones in China and North America is on-going. Anti-aggregation pheromones such as verbenone repel red turpentine beetles. Verbenone acts as a chemical message to D. valens that host food resources are limited. Release rates of the pheromone must be carefully controlled as low release rates of verbenone will actually increase D. valens response to host attractant molecules.Pine monoterpenes are highly attractive to bark beetles (Liu & Dai 2006) and have applications in the monitoring and trapping of beetles. (+)-3-carene and the standard North American D. valens lure of a 1:1:1 ratio of (+) alpha-pinene & beta-pinene (+)-3-carene are effective in attracting D. valens (Erbilgin et al. 2007). The standard lure was used in a mass-trapping program in the Guandi Mountains (west of Shanxi province, China). The proportion of infested forest decreased by 64.4% and the average number of attacks per tree decreased by 59.2% (Guo et al. 2003, in Yan et al. 2005). Ethanol attracts various scolytid beetles including D. valens when released at relatively low or medium concentrations (Yan et al. 2005). A 1:1 ration of ethanol:turpentine captured 60 times more D. valens than turpentine alone (Klepzig et al. 1991, in Yan et al. 2005). 4-Allylanisole (4AA), released by some pines, may prove useful in protecting high-value logs or individual trees by it ability to reduce bark beetle attraction to ethanol (in combination with alpha-pinene & beta-pinene) (Jospeh et al. 2001).
    Insecticides: Fumigation or injection of beetle galleries or spraying of basal tree trunks with insecticides may result in 90 to 98% beetle mortality (Shanxi Forestry Bureau Unpub. Data). Fumigation is costly and difficult and is not effective at controlling beetle populations over large areas. It can result in environmental contamination and decreased natural enemy populations.

    Biological: Research from the Université Libre de Bruxelles showed that Rhizophagus grandis is able to successfully complete its life-cycle with D. valens. R. grandis responds to attractants produced by D. valens, enters D. valens galleries and oviposits a relatively high number of eggs. (LUBIES 2004). Steinernema ceratophorum, a nematode isolated from Jilin province in northeast China, has also produced high infection rates of D. valens larva, causing a larval mortality rate of 90% (Jian et al. 2002).

    Please follow this link for detailed information on the management of the Red turpentine beetle (Dendroctonus valens).

    Nutrition
    Bark beetles mine wood, gaining nutrition from the inner bark (the phloem-cambial region) of twigs, branches, trunks and roots of host trees or woody plants (Seybold, Paine & Dreistadt 2008). Red turpentine bark beetles mine the lower trunk and upper root system only. Red turpentine beetle adults bore through the corky outer layer (bark) to the surface of the wood. Larvae emerge to feed on the inner bark tissue between the outer dry bark and the wood; larvae chambers are within the phloem and do not expand significantly into the sapwood (Smith 1971).
    Reproduction
    Dendroctonus valens may lay over a hundred eggs (Yan et al. 2005).
    Lifecycle stages
    The rate of development of Dendroctonus valens is largely dependent on temperature (Smith 1971). In most areas there is at least one generation of D. valens per year. In southern areas at low elevations, there may be as many as three per year (Smith 1971, Vite et al. 1964, Zhang et al. 2002, in Yan et al. 2005; Randall 2006). In northern areas and at high elevations, two years may be required for one generation (Randall 2006). For a time-line of red turpentine beetle showing the overlap in life stages please see Randall. 2006. Red Turpentine Beetle Ecology and Management. Forest Health Protection and State Forestry Organizations (pg 2).
    The following description of life cycle stages is primarily from Smith (1971):

    Adult colonisation: In spring beetles locate suitable plant host by detecting chemicals such as ethanol, monoterpenes (eg: alpha pinene and beta pinene) and pheromones (Byers 1995, LUBIES 2004). The female bores a hole in the bole of the tree and is soon joined by a male. Resin and frass pitch tube are formed on the bark or drop to the ground in pellets. Boring may exceed 2.5cm per day and the gallery may be extended to the larger roots. One or two pairs of beetles may be found per gallery. Beetles remain in their pine for several months, enlarging their galleries laterally.
    Egg stage: 2 weeks in California, USA 1 to 2 weeks in China (Yan et al. 2005). The female red turpentine beetle oviposits (lays its eggs) within the phloem of trees or fresh stumps. Eggs are laid in an elongate mass along the side of the gallery.
    Larval stage: Length = 8 weeks in California, USA; 8 to 10 weeks in China (Yan et al. 2005). Larvae live in groups in communal chambers within the phloem. A unique feature of the beetle is that the larvae are gregarious whereas most other bark beetle larvae maintain separate feeding tunnels. Gregarious insects live and feed in communities (of the same kind). The larvae tunnels appear as irregularly-margined fan-shapes.
    Pupa stage: Length = 1 week in California, USA; 1 to 2 weeks in China (Yan et al. 2005). As larvae complete their feeding they scoop out bits of wood or bark to make separate pupation cells. In the pupal, or resting stage, the wings, legs and antennae are held against the body. Pupation of over-wintering larva begins in early June, and eclosion (emergence) begins in early July; adults can be detected from May to October (Miao et al. 2001 in Yan et al. 2005).
    Adult emergence & flight: Length of young adult stage = 1 week (Yan et al. 2005). Within a few days to several months warm Spring weather induces emerged beetles to bore out, take flight and disperse in the search for a suitable new host. Flight temperature ranges have been recorded from 19 degrees C to 23 degrees C. In relatively warmer regions emergence and new attacks may occur at nearly any time of the year. In colder regions winter hibernation of the adult or larva may occur, often taking place under root bark (Britton and Sun 2002, Wu et al. 2002, in Yan et al. 2005). (Pupae and eggs rarely overwinter.)

    Compiled by: IUCN/SSC Invasive Species Specialist Group (ISSG) with support from the Forestry Division (Council Of Agriculture) Taiwan
    Last Modified: Friday, 13 February 2009


ISSG Landcare Research NBII IUCN University of Auckland