Dendroctonus spp., Ips spp., Orthotomicus spp.
Bark beetles (Family: Curculionidae, Subfamily: Scolytinae) are small (<1/4 inch) insects that bore underneath a tree’s bark to lay eggs in the phloem. Both adults and larvae live and feed in the phloem, disrupting the tree’s ability to transport nutrients. Many species vector pathogenic wilt diseases, while other vector ambrosia fungus which the larva feed on. Most species of bark beetle attack only stressed trees, though in high populations may move to healthy trees. Pinyon Ips beetle (Ips confuses), Southern pine beetle (Dendroctonus frontalis), red turpentine beetle (Dendroctonus valens), & Western pine beetle (Dendroctonus brevicomis) are just some examples of native bark beetles. Mediterranean pine engraver (Orthotomicus erpsus) is an example of an exotic bark beetle.
Susceptible Hosts
Hundreds of tree species including:
- Pine (Pinus spp.)
- Spruce (Picea spp.)
- Douglas Fir (Pseudotsuga menziesii)
Signs of Damage
- Discolored needles fading from green to yellow to reddish-brown before falling to the ground.
- White pitch tubes and/or saw dust at the base of the tree.
- Small diameter emergence holes in bark.
Biology / Lifecycle
- Females bore through the bark and create galleries under the bark where they mate and lay eggs.
- Eggs hatch and the grubs feed in the inner bark.
- Mature larvae move to the outer bark to pupate.
- Adults emerge through small holes they chew through the bark.
- After emergence adults fly to find new host trees.
- Adults produce pheromone that attracts other beetles to tree.
- Up to 8 generations per year.
- On average 55 days for the insect to complete one generation but can be faster depending upon temperature.
- All life stages can be found overwintering in trees.
Eastern 5 spine engraver beetle
Gerald J. Lenhard, Louisiana State University, Bugwood.org
Pitch tube protruding from stem
Symptoms of Ips bark beetle attack
Whitney Cranshaw, Colorado State University, Bugwood.org
Treatment Strategy/Expectations
Prevention is the most reliable method available. Trunk and limb bark sprays have traditionally been the industry standard for this pest; however, arborists have recently begun using emamectin benzoate on high-value trees that can be root flare injected. Trees that are adjacent to or near infested trees should be considered for preventive treatment.
Maintaining tree vigor can help. Most native species will not attack healthy trees, but attack weakened, dying, or dead trees. Cambistat can also be used to promote tree health and reduce the incidence and severity of stress-mediated diseases and insect problems on trees growing in urban areas. Cultural treatments (e.g. root collar excavation, proper irrigation, soil management, etc.) need to be considered to improve/maintain plant health.
Some exotic species will attack both weakened and healthy trees.
| Product | App. Method | Dosage | Timing | Re-Treatment | Phen. |
| Tree injection | Refer to label. Varies based on tree size and insect pressure | Prior to beetle attack and during periods of optimal tree translocation and when soil has adequate soil moisture | Every other season | Forsythia bloom/red bud bloom | |
| Trunk and limb spray | 2-5 quarts per 100 gallons | Prior to adult emergence & dispersion | 30-60 day intervals | Forsythia bloom/red bud bloom | |
| Trunk and limb spray | 1-2 pints per 100 gallons | Prior to adult emergence & dispersion | 30-60 day intervals | Forsythia bloom/red bud bloom |
*Emamectin benzoate works well to kill the insect but does not prevent the transmission of pathogenic fungus like blue stain (Ophiostoma spp. & Ceratocystis spp.). Research has shown that applying 10ml of Propiconazole 14.3% (e.g. Alamo) per inch DBH can reduce blue stain fungus in pines.
Reach out to Rainbow Ecoscience Technical Support for additional protocol support.
Trunk injection with Quantum
Lower trunk spray
Foliar spray with Maruyama
Always refer to product label for rates and approved uses. Some images courtesy of forestryimages.org or Wikimedia Commons. Use of the images does not imply endorsement of treatments.
