In 1987, researchers began tracking 34 Monterey pines (Pinus radiata) at Soquel High School, just a few miles from the coast. By 2000, 11 of those pines were dead.
Every one of them had something else in common: bark beetles had colonized them. Red turpentine beetles attacked near the base of the trees, while Ips beetles colonized the trunks above.
But the beetles weren’t the whole story. The trees were also affected by pitch canker and a years-long drought that researchers flagged as a likely factor.
Nearly four decades later, that distinction still matters when a tree on your property begins to decline. Bark beetles may be killing the tree, taking advantage of one that’s already in trouble, or both. Knowing which beetle you’re dealing with can help reveal what’s going wrong and whether there’s still time to help it.
Which Bark Beetles Are Killing Bay Area Trees?
Several bark beetle species threaten Bay Area trees. Different beetle species target different tree species, and even those that share a host don’t always behave the same way.
Some can overwhelm living trees when conditions are right. Others are more likely to show up after drought, disease, fire, root damage, or another source of stress has already weakened the tree.
That makes the tree itself one of the first clues.
A beetle attacking a Monterey pine in Santa Cruz may be very different from one colonizing a declining oak. Where the beetle attacks, the damage it leaves behind, and the tree’s condition can help narrow down what’s happening.
Here are some of the bark beetles Bay Area property owners should know.
Red Turpentine Beetle
Red turpentine beetles (Dendroctonus valens) are especially common in Monterey pines planted within about 100 miles of the California coast. They attack most species of pine, but unlike more aggressive bark beetles, they rarely kill a healthy, mature tree on their own.
Instead, their presence is often a clue that something else has already put the tree under stress. Drought, fire, root disease, injury, and poor growing conditions can all make a pine more inviting to these native beetles.
If you suspect red turpentine beetles, look low. They typically attack the lower trunk, root collar, and even large roots below the soil line.
One of the easiest signs to spot is a large pinkish, reddish-brown, or whitish pitch tube where the beetle has bored through the bark. You may also find reddish-brown boring dust in bark crevices or around the base of the tree.
A few attacks don’t necessarily mean the tree is lost. Healthy pines can often withstand limited red turpentine beetle activity. Heavy attacks, on the other hand, are more concerning, particularly when other bark beetles are present.
Ips Engraver Beetles
Ips engraver beetles (Ips spp.) are among the most common bark beetles attacking pines in California landscapes.
Several species occur in the state, including the California five-spined ips (Ips paraconfusus) and Monterey pine ips (Ips mexicanus), the two species associated with the dying Monterey pines in the Santa Cruz County study.
While red turpentine beetles tend to work near the base of a pine, Ips beetles generally attack higher on the trunk and in larger branches.
Look for reddish-brown boring dust caught in bark crevices or collecting beneath the tree. If the bark is removed, their galleries often form distinctive branching or wishbone-shaped patterns in the inner bark. A fading or reddish-brown crown can be another sign that an infestation has progressed.
Ips beetles are particularly drawn to stressed trees and freshly cut pine material. Drought, disease, fire damage, and other injuries can give them an opening, but large numbers of beetles can overwhelm even otherwise-healthy trees.
Ips Beetles: Double the Trouble
Research has shown that both I. paraconfusus and I. mexicanus can vector the fungus that causes pitch canker. That means these beetles don’t simply take advantage of some diseased pines; they can also help move the pathogen into fresh wounds on other trees.
Western Oak Bark Beetle
Pines aren’t the only Bay Area trees vulnerable to bark beetles. The native western oak bark beetle (Pseudopityophthorus pubipennis) attacks several oak species, including one of the region’s most familiar trees, the coast live oak (Quercus agrifolia).
Like red turpentine and Ips beetles, western oak bark beetles are often drawn to trees that are already struggling. They typically colonize stressed, dying, or dead portions of an oak, where the adults tunnel through the bark and the larvae feed on tissues just beneath it.
Western oak bark beetles can also spread Geosmithia pallida, the fungus that causes foamy bark canker in coast live oaks. Early symptoms can include reddish sap oozing from beetle entry holes, followed by the cream-colored foam that gives the disease its name.
That relationship makes western oak bark beetle activity worth investigating rather than treating as an isolated insect problem.
How to Tell if Bark Beetles Are Attacking Your Tree
Part of the problem with bark beetles is that they live, well, under the bark. Point being, you may never see the beetles themselves. So, you’ll have to look for other signs and symptoms of their presence.
The first clues are often what they leave behind or how the tree responds. Not every sign means an attack was successful, either. A healthy pine, for example, may be able to push an invading beetle back out with resin.
If you suspect bark beetles, look for these signs and symptoms:
- Pitch tubes or oozing sap. Pines often release resin where beetles attempt to enter the bark. A pitch tube can show that a beetle attacked, but it doesn’t necessarily mean the beetle succeeded in colonizing the tree.
- Boring dust or frass. As beetles tunnel into the tree, fine reddish or brown material may collect in bark crevices, spiderwebs, or around the base of the trunk. It can look a little like sawdust or coffee grounds.
- Small holes in the bark. Depending on the species and stage of infestation, you may find tiny entrance or emergence holes scattered across affected portions of the trunk or branches.
- Galleries beneath the bark. Bark beetles create distinctive tunnels as adults and larvae feed and reproduce beneath the surface. The pattern varies by species, which can make galleries an important identification clue.
- Changes in the canopy. Needles or leaves that fade from green to yellow, red, or brown can signal that the tree is declining. Thinning foliage and branch dieback can also appear as damage progresses.
Canopy discoloration can be a relatively late sign of trouble. That’s why the less dramatic clues on the trunk can matter. Pitch, boring dust, or new holes may be visible before decline becomes obvious from across the yard.
Can a Tree with Bark Beetles Be Saved?
Sometimes, treatments can help save a beetle-infested tree, but identifying the problem early is important.
A few isolated attacks don’t necessarily mean a tree is dying, especially if it’s otherwise healthy enough to defend itself. The outlook changes once beetles have successfully colonized large portions of the trunk or the canopy has begun to decline.
At that point, there isn’t a treatment that can undo damage already occurring beneath the bark. Preventive insecticide treatments may help protect certain healthy, uninfested trees, but they generally can’t save a heavily infested tree.
That’s why it helps to look beyond the beetles themselves. Drought stress, root damage, disease, fire injury, or poor growing conditions may still need attention even when an infestation is caught early. An ISA-certified arborist can assess how far the beetles have progressed, look for underlying problems, and determine whether the tree has a reasonable chance of recovery.
If a tree is already dead or too severely damaged to recover, removal may be the safest option. Dead or severely compromised trees can shed branches or become structurally unstable, and in fire-prone areas, dead vegetation can also add to the fuel around a home.
How to Protect Your Trees from Bark Beetles
For many bark beetles, prevention starts with something much bigger than the beetle: the health of the tree. A vigorous tree is better equipped to resist attacks, while prolonged drought, injury, disease, and other stresses can tip the advantage toward the insects.
You can help make your trees less vulnerable by:
- Watering appropriately during dry periods. The goal is to support the tree through drought stress without overwatering or creating other root problems.
- Protecting trunks and roots from injury. Construction, soil compaction, equipment damage, and improper pruning can create additional stress or entry points for pests and pathogens.
- Managing cut or infested wood carefully. Fresh or infested material can provide breeding sites for bark beetles, so don’t pile it beside susceptible trees.
- Addressing the underlying problem. If disease, irrigation problems, fire damage, or another stressor is weakening the tree, controlling beetles alone won’t necessarily solve it.
The goal isn’t to make a landscape beetle-free. Bark beetles are native parts of California ecosystems, and many spend much of their time in dead, dying, or stressed wood.
The bigger concern is keeping vulnerable trees from becoming easy hosts and recognizing when beetle activity signals a more serious problem.
FAQs About Bark Beetles in the Bay Area
Bark beetle activity can raise plenty of questions, especially when you’re trying to determine whether a tree is under attack or already in decline. Here are answers to a few questions you may still have about these pests:
Do bark beetles attack healthy trees?
Most bark beetles are more likely to successfully colonize trees that are already stressed, injured, diseased, or declining.
But that doesn’t mean a healthy-looking tree is completely safe. Some species can overwhelm living trees when beetle populations are high, and stress isn’t always obvious from the outside.
Do bark beetles spread from tree to tree?
They can. Adult bark beetles fly in search of suitable hosts, and some species use chemical signals that attract additional beetles to a tree once an attack begins.
Infested logs, branches, or firewood can also provide breeding material for certain species, which is one reason proper handling of infested wood matters.
Does watering a tree get rid of bark beetles?
No. Appropriate watering can help a drought-stressed tree maintain the vigor it needs to resist some attacks, but watering isn’t a treatment for an established bark beetle infestation.
Once beetles are successfully reproducing beneath the bark, simply giving the tree more water won’t remove them or repair damaged tissue.
Should a bark beetle-infested tree be removed?
Not automatically. The decision depends on the beetle involved, how extensive the infestation is, the tree’s overall health, and whether it poses a safety risk.
A tree that has repelled a few attacks is a very different situation from one with widespread colonization and a rapidly declining canopy.
Worried About Bark Beetles? Let Adney Take a Look
Bark beetle activity doesn’t always mean a tree is dying, but it does warrant a closer look.
The sooner you know which beetle is present and what may be making the tree vulnerable, the more options you may have for protecting its health or addressing a potential hazard.
If you’ve noticed pitch tubes, boring dust, canopy decline, or other signs of beetle activity, an on-site evaluation can help determine what’s happening. Our ISA-certified arborists can assess the tree, look for underlying stress or disease, and recommend the appropriate next steps.
Contact Adney Tree Service today to have your trees evaluated and receive a free, itemized estimate.
Sources and References
- International Society of Arboriculture – “Impact of Pitch Canker on Ornamental Monterey Pines in Santa Cruz County, California, U.S., 1987–2000”
Long-term study of Monterey pines in Santa Cruz County examining pitch canker, tree mortality, drought, and bark beetle colonization. Provides the local mortality data and red turpentine and Ips beetle findings discussed in this article.
https://joa.isa-arbor.com/request.asp?ArticleID=2943&JournalID=1&Type=2 - UC IPM – “Bark Beetles”
Research-based guidance covering California bark beetle identification, host trees, signs of attack, tree-stress relationships, prevention, and management. Includes detailed information on red turpentine beetles and Ips engraver beetles.
https://ipm.ucanr.edu/home-and-landscape/bark-beetles/ - California Forest Pest Council – “Bark Beetles”
California forest pest reference covering the hosts, biology, damage, and management of bark beetles found throughout the state. Provides species-specific information on red turpentine beetles, Ips engravers, and western oak bark beetles.
https://www.caforestpestcouncil.org/bark-beetles - PubMed / Plant Disease – “First Report of Geosmithia pallida Causing Foamy Bark Canker, a New Disease on Coast Live Oak (Quercus agrifolia), in Association with Pseudopityophthorus pubipennis in California”
Peer-reviewed research documenting foamy bark canker in California coast live oaks and its association with western oak bark beetle. Describes characteristic symptoms and identifies Geosmithia pallida as the causal fungus.
https://pubmed.ncbi.nlm.nih.gov/30699637/ - The Canadian Entomologist – “Engraver Beetles (Scolytidae: Ips Species) as Vectors of the Pitch Canker Fungus, Fusarium subglutinans”
Peer-reviewed research examining the role of Ips engraver beetles in spreading the pitch canker fungus. Documents transmission by Ips paraconfusus and Ips mexicanus in California pines.
https://www.cambridge.org/core/journals/canadian-entomologist/article/abs/engraver-beetles-scolytidae-ips-species-as-vectors-of-the-pitch-canker-fungus-fusarium-subglutinans/E99BF7E2ADA031F9CC15A237FB7319C6
