Scolytus schevyrewi
(banded elm bark beetle)

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.

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.

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

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).

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).

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).

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.

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.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

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.