When we talk about signs and symptoms in forest health, we are referring to the clues used to help diagnose a tree health problem.

Signs

Signs are physical evidence of the pest itself. General examples of signs include:

Insect or animal evidence
- Holes in bark or chewed in leaves
- Frass
- Actual insects present causing damage
Fruiting bodies of fungi
- Conks
- Mushrooms
Bacterial ooze

Signs of bark beetle activity include:

Boring dust accumulating in bark fissures or at base of tree (finer than that of wood borers, also usually reddish-brown in color)
Galleries beneath the bark
Actual beetles (any lifestage)

: Bark beetle galleries. Photo by Edward H. Holsten, USDA Forest Service, Bugwood.org

: Reddish-brown boring dust created by bark beetles. Photo by Edward H. Holsten, USDA Forest Service, Bugwood.org

Symptoms

Symptoms are the plant’s response to a pest. General examples of symptoms include:

Leaf discoloration, spots, or distortion
Branch dieback
Stem lesions
Galls
Dead stems

Symptoms of bark beetle activity include:

Fading needle color. Color usually changes from green to yellow to reddish-brown.
Pitch tubes on main stem

A pitch tube resulting from a bark beetle attack. Photo by Darren Blackford, USDA Forest Service, Bugwood.org

Symptoms for multiple pests/disorders can be similar. Never confirm a diagnosis on symptoms alone!

Invasive bark beetles

Bark beetles can be unintentionally moved from place to place in several ways. Common pathways for introduction include:

In solid wood packing material
In living plants
In firewood
In bark-on wood products

Invasive bark beetles are challenging in similar ways as other invasive species. Invasive bark beetles may overlap in host preferences and timing with native bark beetles and other pests making it difficult to distinguish or isolate damage between different pests. Invasive bark beetles may also vector potentially invasive pathogens, and invasive bark beetles lack natural enemies in their new location that would help to keep their populations in check. Additionally, bark beetles are very small and invasive ones may be difficult to distinguish from our native bark beetle species.

A few invasive bark beetles threaten Alaskan forests. While none have been detected or currently exist in Alaska, they all pose a threat and could be introduced through travel or trade.

An important bark beetle of concern for Alaska’s forests is the European spruce bark beetle, Ips typographus.

Ips typographus infestation (the yellow-ish tan trees) in Norway spruce. Photo by Daniela Lupastean, University of Suceava, Bugwood.org

The European spruce bark beetle (ESBB) is considered one of the most destructive spruce pests in Europe. While ESBB is not established in the United States, it has been detected at ports and is a target of Early Detection Rapid Response (EDRR) trapping efforts in the state.

ESBB attacks spruce, pine, larch, and fir hosts, though they prefer spruce, and attacks mainly occur in the lower to middle parts of the stem.

Ips typographus adult. Adult beetles are between ⅛ and ¼ inch long. Photo by Jim Stimmel, Pensylvania Department of Agriculture, Bugwood.org

ESBB adults are around 3/16 inch long, cylindrical, brown beetles. The larvae are white, legless grubs similar in size to the adults. Because of their size and the general difficulty of identifying bark beetles, species-level identifications must be made from adult specimens by trained taxonomists. Several species native to Alaska may look similar to the European spruce bark beetle.

Signs and Symptoms of ESBB include:

Pitch tubes and boring dust on bark surfaces
Fading foliage in the crown (green to yellow to reddish-brown)
Galleries under the bark
Blue-stain in woody tissue under bark
Round exit holes (~1/10 inch diameter)

These signs and symptoms are fairly consistent for most bark beetles. Native species producing similar symptoms include the spruce bark beetle and the northern spruce engraver.

Our native spruce bark beetle will differ significantly by size. Spruce bark beetles are longer and wider and will not have the distinct declivity (scooped out rear end) that is characteristic of Ips and a few other closely related genera.

Spruce beetle adult. Note the rounded posterior and the head is not completely covered. Photo by Steven Valley, Oregon Department of Agriculture, Bugwood.org

Ips typographus adult. Note the scooped appearance to the posterior end and the head is slightly more concealed. Photo by Jim Stimmel, Pennsylvania Department of Agriculture, Bugwood.org

Closeup of the Ips typographus declivity. While it may be hard to see in this image, each side of the declivity will have four spines. Photo by Jim Stimmel, Pennsylvania Department of Agriculture, Bugwood.org

ESBB is most likely to be confused with one of our native Ips species. We have 5 Ips species in Alaska. Northern spruce engraver, Ips perturbatus, is the species most likely to cause damage and is common in interior Alaska, though it can be found throughout the state where white spruce grows. Northern spruce engraver is smaller than ESBB, between 5/32 and 3/16 inches long.

While ESBB attacks middle parts of the main stem, Northern spruce engraver attacks and kills the upper portion of the main stem. Northern spruce engraver will also attack and kill small diameter trees.

Ips typographus adult. Note the scooped appearance to the posterior end and the head is slightly more concealed. Photo by Jim Stimmel, Pennsylvania Department of Agriculture, Bugwood.org

: Ips perturbatus adult. Photo by Derek Sikes, University of Alaska Museum, accessed from bugguide.net