Bark and Engraver Beetles

Bark beetles are small, cylindrical beetles about the size of a grain of rice. They are
usually dark brown to black. Symptoms of damage include tunnels under loose bark.
Bark and Engraver Beetles - Articles
Bark and Engraver Beetles

Damage from a bark beetle attack. Courtesy of PDA

Ips spp. and Pityogenes hopkinsi Swaine

Hosts

  • Pines

Damage Potential

  • Low (trees in field) to severe (balled-and-burlapped eastern white pine)

Symptoms and Signs

  • Needles turn yellow to red
  • Dying or dead parts of tree or whole dead trees
  • Galleries (tunnels) under loose bark
  • Dry, reddish-brown boring dust in bark crevices and around gallery openings on main trunk
  • White larvae or dark brown adult beetles in the galleries

Causes of Similar Symptoms

  • Pine root collar weevil
  • Pine wilt disease
  • Armillaria root rot

Identification

Bark beetles are small, cylindrical beetles about the size of a grain of rice. They are usually dark brown to black, but newly emerged adults are lighter in color. It may be difficult to see the head on some species. The chestnut brown bark beetle (Pityogenes hopkinsi) is about 1⁄16 inch (1.6 mm) long and is limited to eastern white pine. Ips adults are slightly larger, ranging from 1⁄8 to 3⁄16 inch (3.18 to 4.76 mm) in length. Ips beetles have distinct spines on their posterior end. All species of pine are hosts for one or more species of Ips beetle. The Ips beetles are often referred to as engraver beetles because of the types of galleries they create under the bark.

Larvae of these beetles are legless, creamy white, and have light brown head capsules. They may reach 3⁄16 (4.76 mm) inch long when fully grown, depending on the species.

Biology and Life Cycle

Figure 1. Adult bark beetle. Courtesy of Jim Stimmel, PDA, Bugwood.org (#2120093)

Overwintered males of both engraver (Ips) and bark (Pityogenes) beetles initiate an attack on a tree weakened by disease, environmental conditions, or other pests (Figure 1). Each male chews a small gallery under the bark and deploys an aggregation pheromone, which attracts both sexes of the same species to the target tree (Figure 2). In addition to bringing females for mating, the pheromone attracts more males to begin additional galleries. As a result, the beetles generally attack a single tree en masse (Figure 3). As the beetles enter the gallery, they introduce fungal spores, which quickly germinate. The fungus serves two purposes: (1) food for larvae, and (2) more important, it blocks resin fl ow, the tree’s main defense against bark beetle establishment. Many adults die in the attack, but the tree’s defense is eventually overcome.

Figure 2. Gallery of the bark beetle, Pityogenes hopkinsi. Courtesy of Rayanne D. Lehman, PDA

Figure 3. Bark beetle boring dust on pine trunk (symptom of beetle attack). Courtesy of Jeffrey Eickwort, Florida Department of Agriculture and Consumer Services, Bugwood.org (#5179069)

Females that enter the male’s initial gallery, or nuptial chamber, mate with the male and then continue chewing an egg gallery. Individual eggs are laid in niches along this gallery. When larvae emerge, they each continue a gallery radiating out from their egg niche (Figure 4). Engraver beetles may have Y- or H-shaped galleries in the inner bark. Bark beetles, on the other hand, generally have a star-shaped gallery. Larvae pupate in the galleries (Figure 5) and adults emerge through the bark to continue their life cycle on a different tree.

Figure 4. Engraver beetle (Ips spp.) larva. Courtesy of G. Keith Douce, University of Georgia, Bugwood.org (#1879049)

Figure 5. Ips spp. callow adult, larva, and pupa (from left to right). Courtesy of Roger Anderson, Duke University, Bugwood.org (#0284043)

Engraver beetles can complete a generation in 21–40 days under optimum conditions. How many generations are completed each year is not known. Bark beetles appear to have two main flight periods—one in spring and one later in summer.

Calendar of Activities

Monitoring and Management Strategies

Plantation Establishment

  • Select a site for optimal pine growth.
  • Maintain proper spacing when planting.
  • Remove potential breeding material (e.g., mature pines damaged by disease, insects, wind, or other harmful causes) from the perimeter of the block.

Preseason

  • Remove any dead or dying pines that may act as reservoirs of bark beetles.
  • Chip piles or tree residue can also be reservoirs.

Growing Season

  • Pityogenes hopkinsi will attack eastern white pine under stress during and after digging (Figure 6). Maintain adequate moisture to roots and replant as soon as possible to lessen stress.
  • Threshold level: Regulatory concern exists for dug trees. Consult your local state plant inspector for assistance.
  • Maintain tree vigor by fertilizing and irrigating as required.
  • At the end of the season, evaluate results and update records.

Figure 6. Balled-and-burlapped trees awaiting delivery—prime targets for bark beetles. Courtesy of Rayanne D. Lehman, PDA

Control Options

Biological

• Insect parasites and predators and fungal diseases offer some control. Woodpeckers will feed on engraver (Ips) beetles, especially during the winter.

Mechanical

  • Remove and burn, bury, chip, or debark infested parts of trees or dead trees to get rid of the insects.

Biorational

  • No recommendations are available at this time.

Chemical

  • Chemical control is only necessary for high-valued trees in recreational or residential settings. Stressed balled-and-burlapped white pine may require chemical applications during beetle flight periods.