Scolytus schevyrewi
(banded elm bark beetle)

Pictures

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Identity

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Preferred Scientific Name

• Scolytus schevyrewi Semenov, 1902

Preferred Common Name

• banded elm bark beetle

Other Scientific Names

• Eccoptogaster emarginatus Wichmann, 1915
• Eccoptogaster transcaspicus Eggers, 1922
• Scolytus frankei Wichmann, 1915
• Scolytus seulensis Murayamas, 1930

Taxonomic Tree

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• Domain: Eukaryota
•     Kingdom: Metazoa
•         Phylum: Arthropoda
•             Subphylum: Uniramia
•                 Class: Insecta
•                     Order: Coleoptera
•                         Family: Scolytidae
•                             Genus: Scolytus
•                                 Species: Scolytus schevyrewi

Notes on Taxonomy and Nomenclature

Top of page S. schevyrewi was described from specimens collected in western China by T. Semenov in 1902 (Semenov and Petrovic, 1902). This insect has not undergone changes in nomenclature since its original description (Wood and Bright, 1992).

Description

Top of page Eggs

Scolytidae eggs are smooth, ovoid, white and translucent. The eggs of S. schevyrewi are approximately 1 mm long and individually deposited along opposite sides of the egg gallery.

Larvae

All scolytidae larvae are similar in appearance and difficult to separate. They are white, 'C'-shaped and legless. The head capsule is lightly sclerotized and amber with dark, well-developed mouthparts. Each of the abdominal segments has two to three tergal folds and the pleuron is not longitudinally divided. The larvae do not change in appearance as they grow. The larvae of S. schevyrewi undergo five instars and are 4.8-7.5 mm long when mature.

Pupae

Scolytid pupae are white and mummy-like. They are exarate, with legs and wings free from the body. Some species have paired abdominal urogomphi. The elytra are either rugose or smooth, sometimes with a prominent head and thoracic tubercles.

Adults

Beetles of the genus Scolytus are characterized as follows: the eyes are slightly emarginated; the antennal club is large and oval with sutures medially bowed in an acute angle; the pronotum is large; the anterior is constricted; the post and lateral margins are sharply bordered; the elytra are flat with the abdomen rising from the second sternite to the apices; the tibiae are smooth laterally and posses a long curved distal tooth; and the third tarsal segments are bilobed (Grüne, 1979).

S. schevyrewi adults are 3.2-4.2 mm long (average 3.6 mm). They are reddish-brown and the head is black. The frons is slightly protruding with striae running toward the clypeus in the females but with yellow, inwardly curved frontal hairs on the peripheral edges in the males. The elytra are red-brown to black-brown, with slightly runcinate lateral and posterior margins. A slightly darker transverse fascia (band), 1.9 mm long and 1.6 mm wide, may exist in some individuals. The sterna are extremely retracted toward the notum from the second segment and beyond, resulting in an obtuse angle with the first sternite. The process on the second sternite is black, flat and wide at the tip. The seventh tergum of the male contains a pair of long setae (Michalski, 1973; Yin et al., 1984; Li et al., 1987; Wang, 1992).

Distribution

Top of page S. schevyrewi is indigenous to China, Mongolia, Korea, Turkmenistan, Uzbekistan, Tajikistan, Kazakhstan, southern Kyrgyzstan and Asian Russia. This insect is established in parts of central and western USA where infestations were first discovered in 2003.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Risk of Introduction

Top of page The adults are weak fliers and prefer to attack adjacent, freshly cut logs, stumps or host trees that are weakened by diseases, other insects, rodents, drought, extreme temperatures, etc. (Li et al., 1987; Yang et al., 1988; Wang, 1992).

The life stages of this insect that are present in the cambium or bark can easily be transported via international trade in unprocessed elm logs or pallets, wooden crates or dunnage, containing bark strips. The infestations recently detected in the USA probably originated several years prior to their discovery, from infested solid wood packing material used in international trade. This insect was found in the vicinity of solid wood packing material recycling centres near Denver, Colorado (NAPPO, 2003). Nevertheless, no records exist of interceptions of S. schevyrewi at USA ports of entry. However, 102 interceptions of Scolytus sp. were made between 1985 and 2000 from Belgium, Canada, Russia and Italy (Haack, 2001). Some of the interceptions from Russia may have been S. schevyrewi.

Elms (Ulmus spp.), which are the primary hosts of S. schevyrewi, comprise of approximately 45 recognized species found in Eurasia, North and Central America (Little, 1979). Many species of elms are popular ornamental trees in urban areas throughout the temperate regions of the world, including several countries in the southern hemisphere. Elms are also popular species for shelterbelt and windbreak plantings, and veneer quality lumber. The introduction and establishment of another potentially damaging pest of elms, especially one that is a vector of Dutch elm disease, could have widespread impacts on the future use of this group of popular, multi-purpose trees.

Habitat

Top of page S. schevyrewi will attack susceptible host trees in both natural forests and urban situations. Prolonged droughts increase the susceptibility of trees to attack.

Hosts/Species Affected

Top of page S. schevyrewi has a wide host range and has been reported to attack several families of trees.

In Asia, Ulmus spp. (elms) are the primary hosts. Elms that are known hosts of this insect in its geographic range include Ulmus pumila (Siberian elm), Ulmus laevis (European white elm), Ulmus davidiana var. japonica (Japanese elm), Ulmus macrocarpa, Ulmus carpinifolia [Ulmus minor] (European field elm) and Ulmus propinqua [Ulmus japonica]. In North America, Ulmus americana (American elm) and Ulmus thomasii (rock elm) have been reported as hosts.

Other reported hosts in the geographic range of S. schevyrewi include Salix babylonica (Babylon weeping willow), Elaeagnus spp., Caragana korshinskii, Malus pumila (paradise apple), Prunus padus (bird cherry), Prunus ansu (ansu apricot), Prunus salicina (Japanese plum), Prunus persica (momo), Prunus yedoensis (Tokyo cherry), Prunus pseudocerasus (Chinese sour cherry), Prunus glandulosa (dwarf flowering almond), Prunus amygdalus [Prunus dulcis] and Pyrus bretschneideri (Michalski, 1973; Krivolutskaya, 1983; Yin et al., 1984; Li et al., 1987; Yang et al., 1988; Wang, 1992; Bright and Skidmore, 2002).

Host Plants and Other Plants Affected

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Growth Stages

Top of page Vegetative growing stage

Symptoms

Top of page The most evident symptom of infestation by S. schevyrewi is the wilting or fading of the foliage on trees that have been attacked. The trunks of heavily attacked trees are often covered with brown boring dust and occasionally sap flow on the bark surface near the entrance hole. The consumption of inner bark by the larvae leads to its easy peeling and sloughing. The removal of bark will reveal the life stages and characteristic gallery patterns of this insect. The adult beetles can also be found in the outer bark of infested trees. After adult emergence, round exit holes (1.6-2.0 mm in diameter) can be found on the bark surface (Li et al., 1987).

List of Symptoms/Signs

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Biology and Ecology

Top of page The genus Scolytus consists of about 55 species of bark beetles found in the forests of Asia, Europe and North America. Several species are considered to be important pests of either broadleaf or coniferous trees. Economically important species, indigenous to North America, include Scolytus ventralis, Scolytus unispinosus and Scolytus quadrispinosus (Furniss and Carolin, 1977; Drooz, 1985). Scolytus intricatus is a pest of broadleaf trees in Europe and Scolytus morawitzi is a pest of larch in Asia. The smaller European elm bark beetle, Scolytus multistriatus, was introduced into North America during the early part of the twentieth century and is now present over much of Canada and the USA. It is a vector of Dutch elm disease, which is caused by the fungi Ophiostoma ulmi and Ophiostoma novo-ulmi.

In China, S. schevyrewi typically undergoes two to three overlapping generations a year, depending on its location. This insect overwinters as either mature larvae inside the pupal chamber or as adults under the bark. The adults emerge from overwintering sites in late April to early May, and begin to search for and attack suitable host trees. Studies in Tajikistan indicated that S. schevyrewi has three to four generations per year in central Asia (Makhmadzieev and Shukronaev, 1983).

The larvae of the first generation develop in May and June, and become adults by early July. By late August, most second-generation larvae construct pupal chambers and begin to overwinter. However, some individuals continue to develop and complete a third generation before winter if the temperatures are favourable (Li et al., 1987; Yang et al., 1988; Wang, 1992).

Newly developed adults remain in their pupal chambers for 2 to 5 days before boring a 1.6-2.0 mm round exit hole through the bark. Adult emergence mostly occurs between 14.00 h and 20.00 h. The sex ratio is slightly female biased (1.0 females: 0.9 males). The new adults walk along the trunk for the first 30 minutes after emergence and before initiating flight. The adults are most active during warm and sunny weather.

Maturation feeding occurs on the bark at the intersections of tender twigs. However, in Tajikistan, studies on S. schevyrewi and several other species of Scolytus indicated that these insects could reproduce without maturation feeding (Makhmadzieev and Shukronaev, 1983). Following maturation feeding, the females attack host trees by constructing individual entrance holes through the bark. It is believed that the females release a pheromone to attract the males to the entrance hole. Mating occurs on the bark surface at the entrance hole and lasts for 1 to 8 minutes (average of 5 minutes). Both the males and females can mate more than once.

Since mating occurs on the bark surface, the egg galleries do not contain nuptial chambers. Each female constructs a single egg gallery in the cambium with individual egg niches along the gallery wall. The egg gallery is a single, vertical tunnel, typically located above the entrance hole and is an average of 4 to 6 cm (maximum 9 cm) long. The egg niches are closely arranged on each side of the gallery and sealed with a mixture of sawdust and adhesive secretions. The egg galleries usually contain an average of about 60 eggs with a range of 23 to 123 eggs. The females guard the entrance hole of their egg galleries until their death (Li et al., 1987; Wang, 1992).

The eggs hatch in the order in which they were laid. The newly hatched larvae feed in the cambium and construct individual galleries. The larval galleries are at first perpendicular to the egg gallery but later turn upwards or downwards. Some larval galleries meander or cross each other. High larval densities lead to complete girdling of the cambium and eventually tree death. There are five larval instars. When feeding is completed, the mature larvae construct pupal chambers in the outer bark, at the end of their galleries and pupate (Li et al., 1987; Wang, 1992).

The duration of each life stage is related to temperature (Li et al., 1987; Yang et al., 1988; Wang 1992). For example, at 26°C, the egg stage is 3 to 5 days (average 3.8 days), the larval stage is 18 to 23 days (average 21.0 days), the pupal stage is 5 to 7 days (average 6.0 days) and the adult stage is 6 to 43 days (average 20 days). Typically, 40 to 45 days are required to complete one generation under field conditions (Wang, 1992).

Notes on Natural Enemies

Top of page In China, a complex of natural enemies, including an ectoparasitic mite on the adults and species of hymenopterous parasitoids on the larvae: Cheiropachus sp. and an unidentified braconid, may contribute to maintaining stable populations of S. schevyrewi (Yang et al., 1988; Wang, 1992).

Plant Trade

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Wood Packaging

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Impact

Top of page In its native habitat in Asia, S. schevyrewi usually attacks weakened or stressed trees (Krivolutskaya and Kupyanskaya, 1970; Michalski, 1973; Li et al., 1987; Yang et al., 1988; Wang, 1992), although during outbreaks it can also attack healthy elms (Ulmus spp.) (Krivolutskaya and Kupyanskaya, 1970; Liu, 1988). Trees older than 4 years, with trunks or branches greater than 5 cm in diameter, are most likely to be attacked, especially in open areas or urban settings (Li et al., 1987; Yang et al., 1988). Typically, young trees or healthy trees are more resistant to attack (Shi and Chen, 1990). Occasional outbreaks can occur that result in widespread tree mortality. In the Karamay region of the Xinjiang Province, China, S. schevyrewi is a major pest of elm trees and has caused an average of 3-5% tree mortality of urban elms and 20-25% mortality of rural elms (Li et al., 1987).

Observations along the northern Colorado Front Range, USA, indicated that S. schevyrewi is invading and killing ornamental elms in urban ecosystems (R Haack, USDA, personal communication, 2003). Some of its host trees, such as Ulmus pumila and Salix spp. are widely used as ornamental trees, as well as for windbreaks and shelterbelt-plantings, throughout much of central and western North America. The establishment of S. schevyrewi in these areas could result in severe damage.

Another economic concern regarding S. schevyrewi is its potential to function as a vector of new species of exotic tree-killing fungi, although none have been isolated to date. In addition, S. schevyrewi could be an efficient vector of the fungi that cause Dutch elm disease: Ophiostoma ulmi and Ophiostoma novo-ulmi. It is possible that S. schevyrewi could serve as a vector of the Dutch elm disease pathogens in areas where the smaller European elm bark beetle, Scolytus multistriatus does not already occur (Shi and Chen, 1990).

Environmental Impact

Top of page Provided that S. schevyrewi confines its attacks to dying or recently killed trees, it functions as one of many insects that are instrumental in the decomposition of dead wood. However, tree mortality during outbreaks can cause ecological disruption and alter the species composition of forests in favour of non-host species. This could result in the loss of biodiversity. Within the geographic range of this insect, the outbreaks are believed to be relatively rare. If this bark beetle becomes a major tree-killing insect in areas where it has been introduced, it could cause a major disruption to the ecosystem in both forest and urban ecosystems.

In the USA, several of its known hosts, including Ulmus pumila and Elaeagnus spp. have escaped cultivation in parts of central and western North America and are considered to be invasive plants. Therefore, this insect has a potential beneficial environmental effect, i.e. causing the death of undesired exotic trees that have escaped cultivation and are displacing native plants.

Detection and Inspection

Top of page The bark surface should be inspected for pitch tubes and/or boring dust. Galleries and insect life stages should be looked for in the cambium and inner bark of unprocessed logs or dunnage, crating or pallets that contain bark strips.

Similarities to Other Species/Conditions

Top of page Scolytus is a large genus of bark beetles and many are similar in appearance and difficult to identify to species. The adults of S. schevyrewi are approximately the same size as the adults of the smaller European elm bark beetle, Scolytus multistriatus. Moreover, the gallery patterns of the two species are somewhat similar in appearance. Preliminary field identification of S. schevyrewi can be made from the presence of the dark bands on the elytra. However, to ensure a positive identification, a taxonomist, with expertise in the family Scolytidae, should examine any bark beetle believed to be a new introduction.

Prevention and Control

Top of page Cultural Control

In Asia, the most effective control method against S. schevyrewi involves the maintenance of tree vigour, coupled with cultural practices such as the sanitation-felling of wilting and dying trees (Li et al., 1987; Yang et al., 1988). Cutting and rapid removal of infested trees before brood emergence and the destruction of bark by chipping have been used to treat infestations in the USA.

Biological Control

Relatively little is known about the natural enemy complex that is associated with S. schevyrewi. Therefore, biological control tactics have not been developed for this insect. However, its recent introduction into the USA and the probable lack of natural enemies in this new environment, make it a candidate for a classical biological control programme.

Chemical Control

Topical insecticide treatment of infested trunks to prevent adult emergence has been carried out in China. Soil drenching with systematic insecticides will reportedly kill the larvae (Li et al., 1987; Yang et al., 1988).

Pheromonal Control

Methods of control using pheromones have not been developed for S. schevyrewi.

Field Monitoring

The adults are attracted to funnel traps baited with either commercial Ips lures (ipsenol and ipsdienol) or Scolytus multistriatus lures [alpha-multistriatin plus 4-methyl-3-heptanol (threo isomer)] and alpha-Cubenene.

Funnel traps, baited with commercial Ips lures, established as part of an USDA APHIS/Forest Service Rapid Detection/Response Pilot Project, led to the initial detection of S. schevyrewi in Colorado and Utah, USA (NAPPO, 2003). Follow-up surveys are presently being carried out with S. multistriatus lures.

Integrated Pest Management

Presently relatively little is known about this insect or its ability to cause severe damage to elms in North America. Existing IPM tactics are limited to monitoring for the occurrence of S. schevyrewi with pheromone-baited traps (ensuring that arborists and extension services in North America are aware of this new potential pest), the rapid removal of infested trees and the destruction of the bark prior to brood emergence.

References

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Bright DE; Skidmore RE, 2002. A catalogue of Scolytidae and Platypodidae (Coleoptera), Supplement 2 (1995-1999). Ottawa, Canada: NRC Research Press, 523 pp.

CABI/EPPO, 2009. Scolytus schevyrewi. [Distribution map]. Distribution Maps of Plant Pests, No.December. Wallingford, UK: CABI, Map 729.

Campos-Bolaños R; Atkinson TH; Cibrian-Tovar D; Méndez-Montiel JT, 2015. First record of Scolytus schevyrewi Semenov (Curculionidae: Scolytinae) in Mexico. (Primer registro de Scolytus schevyrewi Semenov 1902 (Coleoptera: Curculionidae: Scolytinae) en Mexico.) Acta Zoologica Mexicana, 31(1):146-148. http://www1.inecol.edu.mx/azm/2015/1/28AZM31-1-Campos-et-al-.pdf

Drooz AT (Compiler), 1985. Insects of eastern forests. US Department of Agriculture Miscellaneous Publication No. 1426, 618 pp.

EPPO, 2014. PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://www.eppo.int/DATABASES/pqr/pqr.htm

Furniss RL; Carolin VM, 1977. Western Forest Insects. Washington DC, USA: US Department of Agriculture Forest Service, Miscellaneous Publication No. 1339.

Grüne S, 1979. Handbuch zur bestimmung der Europäischen Borkenkäfer (Brief illustrated key to European bark beetles). Hannover, Germany: Verlag M & H Schapfer.

Haack RA, 2001. Intercepted Scolytidae (Coleoptera) at US ports of entry: 1985-200. Integrated Pest Management Reviews 6: 253-282.

Houping Liu; Haack RA, 2003. Scolytus schevyrewi. Exotic Forest Pest Information System (EXFOR). http://spfnic.fs.fed.us/exfor.

Humble LM; John E; Smith J; Zilahi-Balogh GMG; Kimoto T; Noseworthy MK, 2010. First records of the banded elm bark beetle, Scolytus schevyrewi Semenov (Coleoptera: Curculionidae: Scolytinae), in British Columbia. Journal of the Entomological Society of British Columbia, 107:21-24. http://www.sfu.ca/biology/esbc

Krivolutskaya GO; Kupyanskaya AN, 1970. Bark beetles (Coleoptera, Ipidae) in urban shade-tree plantations of Primorskiy Kray. Entomological Research in the Far East 1, 185-195.

Krivolutskaya GP, 1983. Ecological-geographical characteristics of the fauna of bark-beetles (Coleoptera, Scolytidae) of northern Asia. Entomologicheskoe Obozrenie, 62(2):287-301

LaBonte JR, 2010. The banded elm bark beetle, Scolytus schevyrewi Semenov (Coleoptera, Curculionidae, Scolytinae) in North America: a taxonomic review and modifications to the Wood (1982) key to the species of Scolytus Geoffroy in North and Central America. Zookeys, No.56 (Special Iss.):207-218. http://pensoftonline.net/zookeys/index.php/journal/article/view/527/605

Lee JC; Aguayo I; Aslin R; Durham G; Hamud SM; Moltzan BD; Munson AS; Negrón JF; Peterson T; Ragenovich IR; Witcosky JJ; Seybold SJ, 2009. Co-occurrence of the invasive banded and European elm bark beetles (Coleoptera: Scolytidae) in North America. Annals of the Entomological Society of America, 102(3):426-436. http://esa.publisher.ingentaconnect.com/content/esa/aesa/2009/00000102/00000003/art00011

Li Q-X; Jiang X-M; Liu F-Z, 1987. Preliminary study on the biology of elm bark beetle Scolytus schevyrewi (Coleoptera: Scolytidae). Journal of August 1st Agriculture College, (3):12-18.

Little EL, 1979. Checklist of United States trees (Native and naturalized). USDA Forest Service, Agriculture Handbook 541.

Liu H-Z, 1988. Investigation of dying elms with reference to the existence of Dutch elm disease in China. Forest Research, 1:405-413.

Makhmadzieev AM; Shukronaev S, 1983. Characteristics of the development of elm (smooth-leaved elm) bark-beetles (Scolytus) in Tajikistan. Izvestiya Akademii Nauk Tadzhikskoi SSR, No. 4:23-26

Michalski J., 1973. Revision of the paleartic species of the Scolytus Geoffroy (Coleoptera, Scolytidae). Warszava, Krakow: Panstwowe Wydawnictwo Naukowe.

NAPPO, 2003. Detection of Scolytus schevyrewi Semenov in Colorado and Utah. http://www.pestalert.org/notifications.cfm?region=United%20States.

Semenov T-S; Pterovic A, 1902. Novae Sloytidarum species e fauna Rossidae et Asiae centralis (Coleoptera). Entomologicheskowoe Obozrenie, 2:265-273.

Seybold SJ; Downing M, 2009. What risks do invasive bark beetles and woodborers pose to forests of the western United States? A case study of the Mediterranean pine engraver, Orthotomicus erosus. General Technical Report - Pacific Northwest Research Station, USDA Forest Service. The Western Bark Beetle Research Group: a unique collaboration with Forest Health Protection. Proceedings of a symposium at the 2007 Society of American Foresters conference, Portland, Oregon, 23-28 October 2007. Portland, USA: Pacific Northwest Research Station, USDA Forest Service, 111-134.

Shi JL; Chen F, 1990. Breeding behaviour of the bark beetle Scolytus schevyrevi Semenov (Col., Scolytidae) in Ulmus pumila. Journal of Applied Entomology, 109(5):528-530

Wang Z-T, 1992. Scolytus schevyrewi Semenov. In: Xiao G-R, ed. Forest Insects of China (2nd edition). Beijing, China: China Forestry Publishing House, 633-634.

Wood SL, Bright Jr. DE, 1992. A catalog of Scolytidae and Platypodidae (Coleoptera), Part 2: Taxonomic Index. Provo, Utah, USA: Bringham Young University, Great Basin Naturalist Memoir No. 13.

Yang P-H; Hu Z-L; Zhao Z-L; Gao Y-T; Liu Y-J, 1988. A preliminary observation on the bionomics of Scolytus schevyrewi Semenov. Shaanxi Forest Science and Technology, 38-41.

Yin H-F; Huang F-S; Li Z-L; eds, 1984. Economic Insect Fauna of China, Fasc. 29, Coleoptera: Scolytidae. Beijing: Science Press, 205 pp.

Distribution Maps

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