Scolytus schevyrewi

 
IDENTITY
Name:   Scolytus schevyrewi
Pest Authorities:  Semenov
Taxonomic Position:  Insecta: Coleoptera: Scolytidae
Sub-specific Taxon:  
Pest Type:   Insect
Common Name(s):
   Banded elm bark beetle (English)
Synonym(s):
 
RISK RATING SUMMARY
Numerical Score:  9
Relative Risk Rating:  Very High Risk
Uncertainty:   Uncertain
Uncertainty in this assessment results from: Even though Scolytus schevyrewi may have been established in parts of North America for several years, its ability to cause economic and ecological damage to forests, windbreaks, shelterbelts and urban plantings, either through direct tree killing or as a vector of pathogenic fungi, is unknown.

RISK RATING DETAILS
Establishment Potential Is High Risk
The relevant criteria chosen for this organism are:  
  • Organism has successfully established in location(s) outside its native distribution
  • Suitable climatic conditions and suitable host material coincide with ports of entry or major destinations.
  • Organism has active, directed host searching capability or is vectored by an organism with directed, host searching capability.
  • Organism has high inoculum potential or high likelihood of reproducing after entry.
Justification: Scolytus schevyrewi was detected in Colorado and Utah, U.S. between April and May 2003. Since this insect is indigenous to the temperate regions of eastern Asia, it would find many areas of North America with climatic conditions suitable for survival. This insect would also find some of its indigenous hosts, such as Siberian elm and Russian olive, readily available in parts of North America. S. schevyrewi has a directed host searching capacity and an established record of reproducing after it is introduced.

Spread Potential Is High Risk
The relevant criteria chosen for this organism are:  
  • Organism is capable of dispersing more than several km per year through its own movement or by abiotic factors (such as wind, water or vectors).
  • Organism has demonstrated the ability for redistribution through human-assisted transport.
  • Organism has a high reproductive potential
  • Potential hosts have contiguous distribution.
  • Newly established populations may go undetected for many years due to cryptic nature, concealed activity, slow development of damage symptoms, or misdiagnosis.
  • Eradication techniques are unknown, infeasible, or expected to be ineffective.
  • Organism has broad host range.
Justification: Adults apparently are weak fliers and prefer to attack trees in close proximity to trees from which they emerged. However, they are subject to dispersal by air currents. This insect can be transported in wood products made from host trees containing strips of bark via international trade. It has a high reproductive potential and a wide host range, which includes several trees that are widely used as ornamentals or for windbreak and shelterbelt plantings. Consequently Scolytus schevyrewi would find hosts with more or less contiguous distributions. This insect breeds in the cambium of host trees and is cryptic. Moreover, both adults and galleries are similar in appearance to the smaller European elm bark beetle, Scolytus multistriatus, which has been present in North America since the early part of the 20th century. Therefore infestations could go undetected for long periods. This would make eradication or containment extremely difficult.

Economic Potential Is High Risk
The relevant criteria chosen for this organism are:  
  • Organism attacks hosts or products with significant commercial value (such as for timber, pulp, or wood products.
  • Organism directly causes tree mortality or predisposes host to mortality by other organisms.
  • Damage by organism causes a decrease in value of the host affected, for instance, by lowering its market price, increasing cost of production, maintenance, or mitigation, or reducing value of property where it is located.
  • Organism may cause loss of markets (domestic or foreign) due to presence and quarantine significant status.
  • No effective control measure exists.
  • Organism has potential to be a more efficient vector of a native or introduced pest.
Justification: Observations made during the summer of 2003 indicate that Scolytus schevyrewi is attacking and killing live elms in communities along the northern Colorado Front Range (Seybold and Negron 2003). Another economic concern regarding S. schevyrewi is its potential to be a vector of new species of exotic tree-killing fungi, although none have been isolated to date. In addition, S. schevyrewi may serve as an efficient vector of the fungi that cause Dutch elm disease, Ophiostoma ulmi and O. 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, S. multistriatus does not already occur (Shi and Chen 1990). Some of its host trees, such as Siberian elm, Ulmus pumila and willow, Salix spp. are widely used as ornamental trees, as well as for windbreaks and shelterbelt plantings throughout much of central and western North America. .

Environmental Potential Is High Risk
The relevant criteria chosen for this organism are:  
  • Organism is expected to cause significant direct environmental effects, such as extensive ecological disruption or large scale reduction of biodiversity.
  • Organism is expected to have indirect impacts on species listed by Federal, Provincial, or State agencies as endangered, threatened, or candidate. This may include disruption of sensitive or critical habitat.
  • Introduction of the organism would likely result in control/eradication programs that may have potential adverse environmental affects.
Justification: This insect could attack and kill a wide range of host trees, especially elms and willows, and could result in significant environmental changes in many urban and rural areas in North America, especially following climatic anomalies such as extended droughts. Several of its known hosts, including Siberian elm and Russian olive, have escaped cultivation in portions of central and western North America and are classified as invasive species. Therefore, this insect has the potential to attack and kill exotic trees that have escaped cultivation and are displacing native plants.

 
HOSTS
In Asia, elms (Family Ulmaceae) are the primary hosts of Scolytus schevyrewi. These include include Siberian elm, Ulmus pumila; European white elm, Ulmus laevis; Japanese elm, Ulmus davidiana var. japonica; bigfruit elm, Ulmus macrocarpa; smooth-leaved elm, Ulmus carpinifolia and Ulmus propinqua.

Other reported hosts in Asia are weeping willow, Salix babylonia (Family Salicaceae); Russian olive, Eleaganus spp. (Family Elaeagnaceae); peaschrub, Caragana korshinskii (Family Fabaceae); European bird cherry, Prunus padus; apricot, Prunus armeniaca var. ansu; Santa Rosa plum, Prunus salicina; peach, Prunus persica; Yedo flowering cherry, Prunus yedoensis; and Prunus pseudocerasus (Family Rosaceae) (Krivolutskaya 1983, Li et al. 1987, Michalski 1973, Wang 1992, Yang et al. 1988, Yin et al. 1984).

In Colorado, U.S., Siberian elm and at least two species of indigenous elms, American elm, Ulmus americana and rock elm, Ulmus thomasi have been reported as hosts (Negron 2003).

 
GEOGRAPHICAL DISTRIBUTION
Asia:
     Scolytus schevyrewi is indigenous to China (Heilongjiang, Hebei, Henan, Shaanxi, Ningxia, and Xinjiang Provinces), Mongolia, Korea, Turkmenistan, Uzbekistan, Tajikistan, Kazakhstan, southern Kyrgyzstan and Russia (Pribaikalye, Zabaikalye, Primorye, Cisbaikalia, and Transbailkalia) (Krivolutskaya 1983, Michalski 1973, Wang 1992, Yin et al. 1984).
North America:
      Adults identified as Scolytus schevyrewi, were collected in pheromone traps established in two sites in Denver, Colorado and four sites in Utah during April and May 2003. These traps were part of the USDA APHIS/Forest Service Rapid Detection/Response Pilot Project (NAPPO 2003). Subsequent surveys have established its presence in Colorado (Denver, Fort Collins, Fort Lupton) (Ragenovitch 2003); Kansas (11 counties stretching from Garden City in the southwest to Kansas City in the northeast) (Miller 2003); New Mexico (Albuquerque and Santa Fe) (LaBonte 2003) and Utah (Ogden, Price, Logan, Salt Lake City, Clearfield and Smithfield) (Ragenovich 2003).
 
BIOLOGY
The genus Scolytus is a large genus of bark beetles (approximately 55 species) found in the forests of Asia, Europe and North America. Several members of this genus are considered important pests of either broadleaf or coniferous trees. Economically important species indigenous to North America include the fir engraver, Scolytus ventralis, the Douglas-fir engraver, S. unispinosus and the hickory bark beetle, Scolytus quadrispinosus (Drooz 1985, Furniss and Carolin 1977). The smaller European elm bark beetle, Scolytus multistriatus, a vector of Dutch elm disease, caused by the fungi Ophiostoma ulmi and O. novo-ulmi was introduced into North America during the early part of the 20th Century and is now present over much of Canada and the U.S.

In China, Scolytus schevyrewi typically undergoes 2-3 overlapping generations a year depending on its geographical location. This insect overwinters as either mature larvae inside the pupal chamber or as adults under the bark. Adults emerge from late April to early May.

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 temperatures are favorable (Li et al. 1987, Wang 1992, Yang et al. 1988).

Newly developed adults remain in their pupal chambers for 2-5 days before boring a 1.6-2.0 mm round exit hole through the bark. Adult emergence occurs mostly in the afternoon hours between 14:00 and 20:00. The sex ratio is slightly female biased (females: males = 1.0:0.9). New adults walk along the trunk for the first half hour after emergence before initiating flight. Adults are most active during warm and sunny weather. Maturation feeding occurs on the bark at the crotches of tender twigs. Following maturation feeding, females attack host trees by constructing individual entrance holes through the bark. It is believed that females release a pheromone to attract males to the entrance hole. Mating occurs on the bark surface at the entrance hole and lasts 1 to 8 minutes (average = 5 minutes). Both males and females can mate multiple times.

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 as a single, vertical tunnel, typically located above the entrance hole, and averaging 4 to 6 cm (maximum 9 cm) long. Egg niches are closely arranged on each side of the gallery and sealed with a mixture of sawdust and adhesive secretions. Egg galleries usually contain an average of about 60 eggs with a range of 23 - 123 eggs. Females guard the entrance hole of their egg galleries until their death (Li et al. 1987, Wang 1992).

Eggs hatch in the order in which they were laid. Newly hatched larvae feed in the cambium and construct individual galleries. Larval galleries are at first perpendicular to the egg gallery but later turn upward or downward. Some larval galleries meander or cross each other. High larval densities lead to complete girdling of the cambium. Larvae have five instars. When feeding is completed, mature larvae construct pupal chambers in the outer bark at the end of their galleries (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 3-5 (average 3.8) days, the larval stage, 18-23 (average 21.0) days, the pupal stage 5-7 (average 6.0) days and the adult stage, 6-43 days (average 20). Typically, 40-45 days are required to complete one generation under field conditions (Wang 1992).

In China, a complex of natural enemy species, including an ectoparasitic mite on adults and three species of hymenopterous parasitoids: Cheiropachus sp., Elachistocontrum sp. (Hymenoptera: Pteromalidae), and an unidentified braconid, on larvae, may contribute to maintaining stable populations of Scolytus schevyrewi (Yang et al. 1988, Wang 1992).

 
PEST SIGNIFICANCE
Economic Impact:    Scolytus schevyrewi usually attacks weakened or stressed trees (Krivolutskaya and Kupyanskaya. 1970, Li et al. 1987, Michalski 1973, Wang 1992, Yang et al. 1988), although during outbreaks it can also attack healthy elms (Krivolutskaya and Kupyanskaya 1970, Liu 1988). Trees older than 4 years of age with trunks or branches greater than 5 cm in diameter are the 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 Karamay region of Xinjiang in China, Scolytus schevyrewi is a major pest of elm 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 indicate that Scolytus schevyrewi is invading and killing live elms (Seybold and Negron 2003).

Environmental Impact:   Provided that Scolytus schevyrewi confines its attacks to stressed and dying trees, its adverse environmental impacts could be minimal and it functions as an agent of wood decomposition. Tree mortality can occur during outbreaks and cause some ecological disruption, however they are believed to be relatively rare in this insect’s natural range.

Control:    The most effective control method against Scolytus schevyrewi in Asia involves maintaining good tree vigor as well as cultural practices such as sanitation felling of wilting and dying trees. Topical insecticide treatment of infested trunks can be conducted prior to adult emergence, whereas soil drenching with systematic insecticides will kill the larvae (Li et al. 1987, Yang et al. 1988).

Eradication or pest management measures for this insect in North America would undoubtedly involve removal and destruction of infested trees.

 
DETECTION AND IDENTIFICATION
Symptoms:    The first evidence of infestation is often the wilting or fading of leaves. Upon close examination, trunks of heavily attacked trees are often covered with brown boring dust and occasionally sap flow on the bark surface near the entrance hole. Consumption of the inner bark by larvae leads to the easy peeling and sloughing of the bark. Round exit holes (1.6-2.0 mm in diameter) can also be found on the bark surface after adults have emerged (Li et al. 1987).

Morphology:    Mature larvae are milky-white in color, C-shaped, and 4.8-7.5 mm long. The head capsule is creamy yellow in color, with its posterior portion retracted into the prothorax. Mouthparts are brown.

Adults are 3.2 - 4.2 (average 3.6) mm long. Body color is reddish-brown and the head is black. The frons is slightly protruding with striations running toward the clypeus in females; but with yellow, inwardly curved frontal hairs on the peripheral edges in males. The elytra are red-brown to black-brown in color, 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 adults. The sterna are extremely retracted toward the notum from the 2nd segment and beyond, resulting in an obtuse angle with the 1st sternite. The process on the 2nd sternite is black, flat and wide at the tip. The 7th tergum of male contains a pair of long setae (Li et al. 1987, Mickalski 1973, Wang 1992, Yin et al. 1984).

Testing Methods for Identification:    While the black process on the 2nd sternite and the elytral banding are a somewhat distinctive characteristic for Scolytus schevyrewi, positive identification of this insect should be done by a taxonomist with expertise in the family Scolytidae.

 
MEANS OF MOVEMENT AND DISPERSAL
Adults apparently are weak fliers and prefer to attack adjacent host trees that are weakened by biotic (diseases, other insects, or rodents, etc.) or abiotic (drought, extreme temperatures, etc.) factors, newly felled logs, and high stumps (Li et al 1987, Yang et al. 1988, Wang 1992). Life stages of this insect in the cambium or bark can easily be transported long distances by movement of infested plant material and wood products containing bark strips. The infestation recently detected in the U.S. probably originated several years ago from infested solid wood packing material that was used in international trade. Two of the Colorado locations where this insect was found occurred in the vicinity of solid wood packing material recyclers near Denver (NAPPO 2003, Ragenovich 2003).

 
BIBLIOGRAPHY
Drooz, A.T. 1985. Insects of eastern forests. USDA Forest Service, Miscellaneous Publication 1426, 608 pp.
Furniss, R.L.; Carolin, V.M. 1977. Western forest insects. USDA Forest Service, Miscellaneous Publication 273, 654 pp.
Krivolutskaya, G. O. 1983. Ecological and geographical characteristics of the northern Asian bark beetle fauna (Coleoptera: Scolytidae). Entomological Review 62: 52-67.
Krivolutskaya, G.O.; Kupyanskaya, A.N. 1970. Bark beetles (Coleoptera, Ipidae) in urban shade-tree plantations of Primorskiy Kray. Entomological Research in the Far East 1: 185-195. (in Russian)
LaBonte, J. 2003. E-mail message dated 22 August 2003 describing collections of Scolytus schevyrewi in New Mexico.
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. (In Chinese)
Liu, H-Z. 1988. Investigation of dying elms with reference to the existence of Dutch elm disease in China. Forest Research 1: 405-413. (in Chinese)
Michalski, J. 1973. Revision of the paleartic species of the genus Scolytus Geoffroy (Coleoptera: Scolytidae). Warsaw: Panstwowe Wydawn. Naukowe. Polska Akademia Nauk Zaklad Zoologii Systematycznej i Doswiadczalnej, pp. 49-52. (In English with both Polish keys).
Miller, T. 2003. E-mail messge dated 19 August 2003, describing results of pheromone trapping in Kansas.
NAPPO (North American Plant Protection Organization) 2003. Detection of Scolytus schevyrewi Semenov in Colorado and Utah. On line: http://www.pestalert.org/notifications.cfm?region=United%20States.
Negron, J. 2003. E-mail message to W.M. Ciesla dated 13 August 2003
Ragenovich, I. 2003. Introducing Scolytus schevyrewi. Presentation made at the 47th Southern Forest Insect Work Conference, New Orleans, LA, 29-31 July 2003.
Seybold, S.; Negron, J. 2003. Personal communication to R. Haack dated 11 August 2003.
Shi, Z-L.; Chen, F. 1990. Breeding behavior of the bark beetle Scolytus schevyrewi Semenov (Col., Scolytidae) in Ulmus pumila. Journal of Applied Entomology 109: 528-530.
Wang, Z-T. 1992. Scolytus schevyrewi Semenov. In: Xiao, G-R (editor) Forest Insects of China (2nd edition), Beijing: China Forestry Publishing House, pp 633-634 (In Chinese)
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 1988: 38-41. (In Chinese).
Yin, H-F.; Huang, F-S; Li, Z-L. (Editors) 1984. Economic Insect Fauna of China, Fasc. 29, Coleoptera: Scolytidae. Beijing: Science Press, p. 22 (In Chinese).
 
AUTHOR(s)
Name(s):
Houping Liu
Robert A. Haack 
 
Name and Address of the First Author:
Houping Liu
Entomology
Michigan State University
208 CIPS Building
East Lansing, MI
USA 48824
 
CREATION DATE:        08/07/03
MODIFICATION DATE:        05/06/04

    
Selected images from Forestry Images (www.forestryimages.org)
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1326205
1326205

Adult(s)
Newly introduced species in western US. Found on Elm, caragana, and Russian olive.
Photo by Whitney Cranshaw,
Colorado State University

1326206
1326206

Adult(s)
Newly introduced species in western US. Found on Elm, caragana, and Russian olive.
Photo by Whitney Cranshaw,
Colorado State University