Fir engraver is a native insect and an integral part of Colorado’s mixed-conifer ecosystems, playing a key role in the dynamics of these ecosystems
Fir Engraver Beetle
Fir engraver (Scolytus ventralis) is a bark beetle that attacks and kills true fir tree species (Abies spp.) in western North America. In Colorado, white fir is the only host tree of fir engraver beetles.
Adult males and females are shiny, dark-brown to black beetles, ¹⁄₆-inch (4 mm) long, or about the size of a small grain of rice.
Females construct a horizontal egg gallery perpendicular to the main tree stem. The gallery can range in length from about 4 to 12 inches (10-30 cm).
The larvae feed on the tree phloem (conductive tissue containing carbohydrates) and construct additional side galleries that are oriented vertically, or perpendicular to the original egg gallery.
Symptoms of Infestation
As is the case with most bark beetles, the most conspicuous evidence of fir engraver infestation is the occurrence of dead and dying trees. In Colorado, the foliage of dying white firs fades from a typical blue-green color to a light orange. Outbreaks may consist of a scattering of dead and dying trees, or small groupings of five to 10 trees. Trees with either top-kill or dying branches often can be seen in combination with dead and dying trees. Fir engraver prefers trees that are stressed by other causes, such as root diseases, prolonged periods of drought, defoliating Douglas-fir tussock moths and western spruce budworms, or physical wounds from lightning, snow breakage, other trees falling against them, or human activity.
- These beetles typically prefer trees greater than 4 inches (10 cm) in diameter.
- Entrance holes are frequently located in bark crevices and furrows, and successful attacks are accompanied by the presence of reddish-brown boring dust in bark crevices.
- Streams of clear resin also may flow from entrance holes, and more vigorous trees may exude enough resin to successfully resist beetle attack.
- Once adults emerge from infested trees, the bark surface also will then be covered with tiny exit holes about the size of a pinhead.
It is important to remember that the fir engraver beetle is a native insect in Colorado’s forest ecosystems, and part of an ever-changing forest. However, the potential negative impacts of natural disturbances, such as from this beetle and other insects and diseases, can be reduced through proactive forest management. However, in cases where treatment is necessary, a few options exist including:
- Individual, high-value trees can be protected by spraying the trunk with a preventive pesticide prior to beetle attacks (by mid-May in many parts of Colorado). Be sure the pesticide is registered for use on bark beetles in fir trees, and apply only as directed on the label.
- Mechanical treatments for fir engraver often can be effective, but also time consuming and costly, and may not be practical or effective for all situations. Treatments involve felling infested trees and then destroying larvae through burning, solar radiation, or submergence in water.
Learn More About Fir Engraver Beetle
Fir Engraver Beetle (7 MB PDF) – New 2016