Texas Invasive Species InstituteScolytus schevyrewi
Banded Elm Bark Beetle
Class: Insecta
Order: Coleoptera
Family: Scolytidae
Photographer: Pest and Disease Image Library
Source: Bugwood.org
Adult Description: 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. Adult emergence occurs mostly in the afternoon hours and the sex ratio is slightly female biased. Adults are most active during warm and sunny weather. Once the beetles are mature they feed on the bark at the crotches of tender twigs. Scolytus schevyrewi is small, brown and has dark horizontal bands across its elytra. The dark band can be absent, and when it is, Scolytus schevyrewi does resemble Scolytus multistriatus; which is another invasive beetle that has been established in the United States longer than the banded elm bark beetle.
Larvae Description: In China, Scolytus schevyrewi typically undergoes 2-3 overlapping generations a year depending on its geographical location. Mature larvae are white in color, C-shaped, and 4.8-7.5 mm long. The head capsule is creamy yellow in color with brown mouthparts, and the posterior portion retracted into the prothorax.
Ecological Threat: Adults 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 for landscaping or for windbreak and shelterbelt plantings.
Both adults and pupae galleries are similar in appearance to, 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. 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. As a result, this insect has the potential to attack and kill exotic trees that have escaped cultivation and are displacing native plants. This beetle also transmits the fungal pathogen Ophimostoma novo-ulmi, Dutch elm disease, which is an aggressive fungus that destroys the vascular system of Elm trees, causing the tree to wilt and die.
For more information on Dutch elm disease click here
Biology: 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. Typically, 40-45 days are required to complete one generation under field conditions.
Host Preferences: American, English, Russian and Rock Elm. In the beetle’s native range it attacks elms, willows and woody plants of the pea family.
History: It was first discovered in 2003 in Colorado and Utah and has since expanded to 19 other states including Texas. However, the dual state identification suggests that by 2003 the banded elm beetle wasn’t new to the United States. The earliest museum specimen was collected in 1994 in Denver, Colorado.
U.S. Habitat: Since Scolytus schevyrewi 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 readily available in parts of North America. Scolytus schevyrewi has an established record of reproducing after it is introduced.
Distribution
Native Origin: China, Central Asia and Russia
U.S. Present: AZ, CA, CO, ID, IL, KS, MI, MO, MN, MT, NB, NM, NV, OK, OR, SD, TX, UT and WY
Management
In China, a complex of natural enemy species, including ectoparasitic mitea on adults and species of hymenoptera parasitoids: Cheiropachus sp., Elachistocontrum sp. (Hymenoptera: Pteromalidae), on larvae, may contribute to maintaining stable populations of Scolytus schevyrewi. However, those insects are invasives of the United States and cannot be readily employed. Therefore, the best management is to remove infected Elms early. Prevention management included debarking, chipping and burning cut stems and branches, along with limiting the movement of elm firewood.
Text References
Liu, H-Z. 1988. Investigation of dying elms with reference to the existence of Dutch elm disease in China. Forest Research 1: 405-413.
Internet Sources
