Banded Elm Bark Beetle

Scolytus schevyrewi (Semenov)

A bark beetle affecting elm trees, identified in Cheyenne in 2003, has since been found throughout Cheyenne and areas surrounding Cheyenne. Due to the number of locations that it has been found, the beetle had probably been in Cheyenne for several years prior to 2003. The banded elm bark beetles were found feeding in the cambium layer under the bark on Siberian elm (Ulmus pumila), commonly, but incorrectly known as Chinese elm. The banded elm bark beetle is thought to primarily attack trees under stress. Stress, for example, caused by drought, herbicide damage, hail damage, root damage, or other insect or disease attack.

 
Adult Banded elm bark beetles and larva on a dime.

 
          Adult Banded elm bark beetle showing dark band over the back wing coverings. 
Photos: Cheyenne Forestry Division


The banded elm bark beetle, (Scolytus schevyrewi), originally comes from parts of Russia, Mongolia, China and Korea. It is suspected that the banded elm bark beetle was introduced into the United States in wood packing material such as wooden crates, and pallets.

An article from China states that the banded elm bark beetle overwinters in the tree in mature larva form. The larva will pupate when temperatures exceed 15°C (60°F). Under field conditions it took 41-45 days to complete a generation. A generation consists of these stages: egg, larva, pupa, adult. The larva stage is the most destructive since it feeds on the cambium layer (growth cells under the bark) and phloem cells (food conduction tissue under the bark). The adult banded elm bark beetle emerges from a tree after pupation and can fly to a different tree or unaffected parts of the same tree. The extent of beetle flight and the infestation range can be dependent on prevailing winds. In the banded elm bark beetle's native range there are two to three generations per year. At two discovery sites on September 29, 2003, in Cheyenne, all life stages were present, eggs, larvae, pupae, and adults.

                
Two separate Siberian elm trunks showing the oozing of sap from Banded Elm Bark Beetle entry holes. Sometimes the sap flow pushes out the attacking beetle. If the beetle successfully enters the cambium layer of the tree trunk or limb, eggs are laid. The eggs hatch and the larvae begin to feed in the cambium and phloem layers under the bark. One adult beetle entry hole can equal 20 - 50 exit holes.
Photos: Cheyenne Forestry Division

                                                          
                                     Exit holes in a Siberian elm trunk made by the adult banded elm bark beetle.
                                                   When you see this, the insect is gone and the damage is done.
                                                                        Photo: Wyoming State Forestry Division

Presently, it is not known if the banded elm bark beetle carries Dutch elm disease fungal spores. The European elm bark beetle is a common bark beetle in the area and a known carrier of Dutch elm disease fungal spores. The Scolytus schevyrewi seems to be closely related in formation to the European elm bark beetle (Scolytus multistriatus).

Trees affected by the Banded elm bark beetle in the native range are various species of elm, willow, Caragana (peashrubs), Russian-olive, and some fruit trees in the Prunus genus like plums, and cherries. In Cheyenne, Siberian elms are the only trees known to be attacked, so far.

Control of the Banded elm bark beetle includes: Removing infested wood and burning it immediately, chipping it into small chips, or burying it in a landfill. Chipping the wood will allow the living tree cells to quickly dry out. Adult beetles present in the wood could survive the chipping process and fly away to infect other nearby trees. Chipping is probably not the best solution, although it is better than doing nothing. In no case should the infested wood be stored as firewood. Chemical control for borers in general includes: Surface spraying the trunk to the point of runoff, in mid April, with Astro, a Pyrethroid insecticide or an insecticide containing Carbaryl.

Links:

Colorado State University Cooperative Extension

University of Wyoming - Cooperative Extension Service, publication B-1035 is particularly helpful for tree care. This online publication contains information on: Aphids, Borers, Cottonwood blotch leaf miners, Cytospora canker, Fireblight, Gall makers, Aspen leaf spots, Oystershell scale, Pear slugs, Powdery mildew, and Spider mites.