Forest Health Notes:
A Series for the Non-Industrial Private Forest Landowner

Hosts: Ponderosa pine, lodgepole pine, western white pine, occasionally Engelmann spruce.

Quick ID:

• Galleries have a central nuptial chamber from which 2-3 egg galleries radiate
  
• Galleries free from frass
  
• Yellow or reddish boring dust in bark crevices or on ground
  
• Foliage discoloration
  
• Top-killed trees
  
• Insects small, dark beetles 1/8 to 1/6" in length.

Field Identification

Tree: Yellow or reddish boring dust is found in bark crevices, around entrance holes, or on the ground beneath. Pitch tubes are seldom formed. After attack, the foliage of the tree discolors from green to yellow, reddish, and then reddish brown. This happens rapidly in the summer and more slowly in fall and winter. Ips beetles typically attack near the top of the trunk, and frequently girdle the tree, causing topkill. Galleries mine the bark and score the sapwood. Unlike the galleries of mountain or western pine beetles, ips galleries are free from frass (boring dust and insect droppings). A central nuptial chamber has several egg galleries leading off in different directions.

Insect: Ips beetles are reddish brown to nearly black and from 1/8 to 1/6" in length. The posterior of the abdomen is notched and has pronounced toothlike "spines."

May be confused with: Mountain pine beetle, western pine beetle.

Life cycle: There are a number of species of ips beetles found in Washington. The most common is Ips pini, which is generally found attacking and killing ponderosa and lodgepole pine. Adult insects may attack trees or fresh slash over 2" in diameter. A quantity of fresh slash or debris after a windstorm will almost certainly be used to produce a large beetle population, which may subsequently attack living trees. Fortunately, attacks are of short duration, often confined to a single year. A male bores through the bark to the cambium and constructs a nuptial chamber. Several females then join him and construct separate egg galleries leading off in different directions. Eggs are laid in niches along the sides of these galleries. Larvae hatch and feed in the inner bark, working away from egg galleries. Larval tunnels are packed with frass. Larvae construct oval pupation cells at the end of their tunnels and pupate, emerging as new adults about 1-1/2 to 2 months after hatching. Between two and five generations can be produced in a single year, depending on altitude, latitude and species. Adults may re-emerge after laying eggs and attack a second or even third time in a year. Insects generally overwinter as adults, either in large groups under the bark or in large stumps or bark crevices. Beetles also overwinter in leaf litter on the forest floor.

Predisposing agents: Large numbers develop in fresh slash. Warm, drought-like spring weather will lead to ips damage. Ips beetles frequently attack the tops of trees recently killed by western or mountain pine beetles. Sufficient host material will lead to epidemics where living trees are attacked in groups. These may resemble mountain pine bark beetle kills.

Impact: In 1991, the USFS estimated that an ips outbreak had affected 23 acres in Washington. However, that doesn't reflect the thousands of single trees that were killed by ips infestations too small to be identified by overflying aircraft. Damage occurs most frequently as killing of trees 2 to 8" in diameter and top-kills on older trees.

Management: Direct means of control (e.g. spraying, felling, etc.) are not useful against pine engravers, especially as outbreaks rarely last more than one season. They may be useful in high-value areas like campgrounds or near houses. Outbreaks may be prevented by appropriate slash disposal and thinning in overstocked immature stands. Lopping and scattering slash is the preferred way to dispose of slash from a nutrient cycling standpoint, but can cause problems with ips. However, scattering slash in the open where the sun will dry it out will make it unsuitable as a breeding medium. During the spring and early summer, particularly when precipitation is below normal, slash disposal is critical. Slash should be scattered, not piled, during these times. Windthrown trees should be salvaged promptly. Low fires in late autumn may kill beetles overwintering in leaf litter.

Note: Use pesticides with care. Apply them only to plants, animals, or sites listed on label. When mixing and applying pesticides, follow all label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. If pesticides are spilled on skin or clothing, remove clothing and wash skin thoroughly. Store pesticides in their original containers and keep them out of the reach of children, pets and livestock.