Bark beetles damage trees by boring through the bark and feeding on the cambium layer just beneath it. As they tunnel, they create galleries where eggs are laid, often in the tree’s phloem during mid to late summer. The larvae feed under the bark until reaching the pupal stage, then typically overwinter before emerging as adults.
In addition to physical damage, bark beetles can introduce harmful fungi—such as the one responsible for Dutch Elm Disease—which further compromises tree health. This combination of tunneling and fungal infection disrupts the flow of water and nutrients, weakening the tree and potentially leading to its death if left untreated.
Bark beetle’s four stages to their life cycle:
- Egg
- Larva
- Pupa
- Adult Moth
The life cycles of bark beetles can range from approximately one generation per year to one generation every two years. It varies depending on climate.
Table of Contents
TL;DR: What to be on the lookout for with Bark Beetles?
Answer:
Mountain Pine Beetle
Adults are about 1/4 inch long and brown to black in color. Cylindrical, and stout bodied. Larvae are yellowish white.
Host Trees
- Ponderosa Pine
- Lodgepole Pine
- Limber Pine
Susceptibilities
Mature trees over 8 inches in diameter. Trees under stress from injury, overcrowding, root disease or old age.
Symptoms & Recognition
Masses of resin, or pitch tubes (may be pink, brown, yellow or white) will appear on the trunk around entrance holes. Reddish dust from boring around the tree/on the bark will be present and there might be evidence of a woodpecker feeding. Reddish needles near the crowns may occur (8-10 months after attack). This bug also transmits a bluestain fungi which grows within the tree; gives a blue-gray appearance to sapwood.
Management & Treatment
Woodpeckers, clerid beetles, and extremely cold temperatures are natural ways that they’re managed. Pheromone baiting to concentrate the beetles in one area may make it easier to eradicate the beetles. Preventative measures include: promoting tree health & vigor, diversification of tree species and open spacing when planted. Permethrin sprays can also be used as preventative measures in early July.
Javier E. Mercado, CC BY 4.0, via Wikimedia Commons
Notes
If a fungal colonization occurs in conjunction with larval feeding, host trees can die within a few weeks. Both will aid in girdling the tree, cutting off nutrients and water.
Treatment Window
Turpentine Beetle
Dark reddish brown/black. Larger adults than other bark beetles. Head faces downward. Grubs are legless and creamy white.
Host Trees
- Ponderosa Pine
- Scots Pine
Susceptibilities
Large diameter pines. Trees weakened by drought or construction. Recently transplanted trees. Those already injured or affected by other insects and diseases.
Symptoms & Recognition
Wilted needles. Masses of resin, or pitch tubes (may be pink, amber or white) will appear on the trunk around entrance holes. Exit holes likely on the lower trunk or exposed roots. Boring dust around the tree/on the bark will be present and there might be evidence of a woodpecker feeding.
Management & Treatment
Insecticidal sprays in early spring around the base of the tree before beetles attack. Preventative measures include: avoiding wounding the tree near the base, watering during drought stress, removing nearby infested trees or stumps.
Javier E. Mercado, CC BY 4.0, via Wikimedia Commons
Notes
Turpentine beetles are often secondary invaders, attacking already stressed trees. Severe infestations can contribute to decline or death.
Treatment Window
Douglas Fir Beetle
Adults are similar in appearance to the Mountain Pine beetle. Colors range from black to reddish-brown wing covers. Larvae are legless, whitish grubs with brown heads.
Host Trees
- Douglas Fir
Susceptibilities
Groups of fire or wind-damaged trees. Trees damaged by insect defoliation. Or, healthy stands of trees in a forest with a few infested or weak trees.
Symptoms & Recognition
Pitch streamers will likely appear down the bark. Red or yellow dust from boring will be present either at the base of the tree or nestled in the bark.
Tunnels tend to have characteristic gallery patterns – running perpendicular to egg groupings. Foliage may fade to a deep reddish-brown.
Management & Treatment
Remove already infested trees. Pheromone baiting can be used to concentrate the bark beetles in one area. Preventative measures include: promoting tree health & vigor, avoiding fresh wounds and diversification of tree species and open spacing when planted. Preventative sprays need to be applied by late April.
Notes
Douglas Fir beetles often emerge earlier than Mountain Pine beetles, but most of the population emerges in late June, making it a long emergence period.
Treatment Window
Ash Bark Beetle
Cylindrical, dark brown to black as an adult with fine hairs on the wing covers. Larvae are white and legless with a brown head.
Host Trees
- Green Ash
- White Ash
Susceptibilities
Injured or heavily shaded branches. Transplanted trees. Stressed trees.
Symptoms & Recognition
Sap may be present from ventilation holes constructed during tunnelling. Main egg galleries run perpendicular to branch length. Girdling tunnels may occur around twigs and small branches. This insect allows for the transmission of red-brown wood fungi, which can be found along the wound sites.
Management & Treatment
Clerid beetles, jumping spiders and wasps attack the ash bark beetles. Preventative measures include: promoting tree health & vigor, planting in well sited areas, sprays in mid-spring.
Randy A Nonenmacher, CC BY 4.0, via Wikimedia Commons
Notes
Infestations by borers like the Lilac/Ash borer often make trees more vulnerable to ash bark beetle attacks.
Treatment Window
Spruce Pine/IPS Beetle
In Colorado, there are a variety of species of IPS beetles. 1/8-1/4 inch long. Reddish brown to black. Pronounced cavity at the rear end with several pairs of tooth-like spines. They are similar in appearance to the Mountain Pine Beetle.
Host Trees
- Spruce
- Engelmann Spruce
- Ponderosa Pine
- Lodgepole Pine
- Limber Pine
- Pinyon Pine
- Austrian Pine
Susceptibilities
Weakened trees, transplants, trees previously under beetle attack, drought stressed, over watered, trees with root injuries, recently felled trees, trees already surrounded by an IPS infestation.
Symptoms & Recognition
Yellow to red hued boring dust. Dust
accumulates in crevices of bark and/or base of tree. Possibility of a blue stain fungus which can plug the tree’s tissues. Presence of woodpeckers may be indicative as they enjoy feeding on bark beetles.
Management & Treatment
Preventative measures include promoting vigorous tree growth by planting trees in optimal
places in landscape. Watering and fertilizing are crucial in order to bolster fast and healthy growth. Freshly pruned branches should not be discarded next to healthy trees, as this can attract more beetles. Applying pesticides in March/April will protect your trees for the entire season.
Gilles San Martin, CC BY-SA 2.0, via Wikimedia Commons
Notes
Adult flights of the Spruce Ips beetle have been noted all the way into warm Octobers.
Treatment Window
Plant Health Care Experts
The most effective way to safeguard your trees from insect damage is by combining proper pruning, regular watering, and strategic pest control.
Our Plant Health Care team is skilled at identifying early signs of bark beetle activity and responding quickly to reduce harm. While losing a tree isn’t always unavoidable, it’s a risk we work hard to minimize. If you think your tree may be infested, reach out to the professionals at Front Range Arborists — we’re ready to assist.
Bark Beetles, Moths & Borers
Oh, My
Bark beetles are a major threat to your trees, but they’re not the only ones. It’s important to recognize the signs of bark beetle damage, as well as injuries caused by moths and borers.
Need More?
Want to learn more about insects and how they can negatively impact your trees? CSU Extension has a variety of publications across a range of topics.