Potato Patch Cabinowner's Association

Bark Beetle Infestation

Overview of beetle

Pine Bark Beetles -
Jeff Schalau, County Director, Agent, Agriculture & Natural Resources
Arizona Cooperative Extension, Yavapai County

The forest that stretches from the San Francisco Peaks to Payson and to Prescott is the largest contiguous Ponderosa pine stand in the world. Researchers tell us that the pine forests we see today are not like what we would have seen prior to European settlement. Then, Ponderosa pines grew in park-like stands with grasses and shrubs in the understory. One hundred years of successful fire suppression (thanks to Smokey) has left us with the forests we see today.

As you travel through our Ponderosa pine forests, you can see the affects of this year's drought everywhere. Most noticeable are dead or dying trees either in groups or standing individually. In all likelihood, this mortality was caused by bark beetles. A few dead trees here and there are normal. In fact, drought is a normal condition in the arid southwest and when drought is combined with dense stands of timber, bark beetles can really thrive. I want to provide some more details about the various Ponderosa pine bark beetles so you can appreciate them (and provide some recommendations to keep them from killing pines in your landscape).

There are several species of bark beetles that infest Ponderosa pine in our area. Red turpentine beetles (Dendroctonus valens) generally attack the lower trunk. Engraver beetles (Ips sp.) generally attack the upper portion of the trunk. The male engraver beetle bores into the tree emitting a chemical (pheromone) to attract a female. Then they create a nuptial chamber inside the bark, the couple mates, they create tunnels (egg galleries), the female lays her eggs at the edges of tunnels, and the larvae feed on the inner bark before pupating. In doing so, they interrupt the flow of nutrients in the inner bark (phloem) and cambium killing the tree. After the larvae pupate, they emerge from the host tree and look for new trees to infest. Several generations may breed each summer. The last generation of beetles overwinters as adults under the bark.

Within a few weeks of attack, the needles at the top turn a straw-yellow color. If you look closely, you may also see fine boring dust in the bark crevices and at base of the tree. Pitch tubes (globules of pitch) may also be visible. Removing the bark will expose the galleries and insects if present. The following season, the needles turn a reddish color.

There is nothing that can save a tree once it is attacked by bark beetles. Simply remove infested trees as soon as possible. You may keep the firewood, but the woodpile must be place in a sunny location and covered with heavy, clear plastic which has been sealed at the edges. This will cause heat to build up (160 degrees F) and kill remaining beetles. Individual woodpiles should not be larger than 4 x 4 x 4 feet (1/2 cord). Do not leave slash or other woody debris piles on site. This is an excellent breeding medium for bark beetles.

There are no practical or effective sprays or injections that prevent bark beetle attacks on green trees. Insecticides are not recommended. To protect healthy, high value trees, provide supplemental irrigation to trees during dry periods. This is best accomplished by using a soaker hose placed near the drip line of the tree.

In natural forest situations, pine bark beetles are native insects benefiting the forest by reducing the overall number of trees and making more resources available to those that remain. Dead trees become also breeding grounds for wood boring insects, which provide food and shelter to birds. Down logs also create microenvironments for plants and ground dwelling animals. Remember: dead standing trees are a hazard in most residential landscape situations and should be removed for safety reasons.

The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@verdeonline.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://ag.arizona.edu/yavapai/anr/hort/byg/.



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More details on Beetles

Bark Beetles Biology, Prevention and Control

Jill L. Wilson, Entomologist
USDA Forest Service, Southwestern Region

Bob Celaya, Forest Health Specialist
Arizona State Land Department, Forestry Division

Introduction May 1998

What are bark beetles anyway? Many species of bark beetles affect conifers in the pine forests of Arizona. Of these, the most common ones that one may encounter are the engraver beetles or Ips spp. and Dendroctonus spp., that infest ponderosa pine. These small, cylindrically-shaped insects, are called bark beetles because of their habit of boring in the inner bark, making distinctive galleries or tunnels.

What do they do? The direct effect of bark beetle attack in living trees is tree mortality or sometimes top-killing. In an urban situation, this can be undesirable as the attacked trees may have great value, could become a hazard if not removed, and be expensive to remove. In the forest, beetles can influence resource management in many ways, some positive and some negative. Bark beetles are a natural part of our southwestern forests. They have evolved with ponderosa pine for millenia. In a sense, they function as nature's thinning agents, removing the sick, old or weakened trees. Effects of beetles on wildlife species depend on the species involved.

Dead trees provide habitat for many species which utilize snags for nesting, roosting or foraging. Clumps of dead trees create openings which create habitat for others. Extensive mortality may create habitat for some but may also reduce it for others. Presence of dead trees, especially in large numbers, can also increase fire hazard.

How do I know if my tree is affected? Evidence of attack varies some by species and is discussed later in these notes. In general, if a tree has red boring dust in the bark and small round entrance holes, or pitch tubes, it may be infested. It does take a good number of attacks to kill a tree so just a few pitch tubes or holes on one side usually won't kill a tree. Usually by the time the pine needles change color to reddish brown, the beetles are gone.

Why do we see them kill trees sometimes and not others? Bark beetles are usually associated with stress factors such as drought, disease, or injury. Bark beetle populations may increase when one or more of these stress factors is associated with highly susceptible stand conditions (i.e., dense stands).

What can we do about them? In the long term, preventive strategies are most effective in reducing tree losses. Unacceptable losses can be avoided in most cases by maintaining thrifty, vigorous trees. Thinning dense stands of ponderosa pine so that crowns are no lonser touching, will relieve competitive stress among the remaining trees, making them less susceptible to attack. Proper treatment of pines infected with dwarf mistletoe (a parasitic plant) and removal of trees severely damaged by lightning or construction activities, may also reduce the likelihood of a beetle attack.

In urban settings avoiding damage to tree trunks and roots can also be effective. Damage may be caused by a variety of practices involved in construction activities, including changing grade levels, trenching, soil compaction, paving, etc. Once a tree has been successfully colonized by bark beetles, it cannot be saved. In some situations, removal of infested trees prior to emergence of brood is recommended in an attempt to protect surrounding trees. However, the overall effectiveness of this strategy is unproven. Further, in most forest situations, it is not feasible to locate and remove all trees prior to emergence.

Ips beetles may complete one generation in one month during the summer. If trees are cut, they must either be removed from the site, or if left, the bark should be stripped off to kill the developing beetle brood. Covering the wood with clear, heavy plastic is also effective. Trees can also be protected from attack by bark beetles during particularly hazardous times through the application of pesticides. The entire bole (trunk) of the tree must be covered in order to provide protection. Carbaryl (Sevin) is registered for this purpose for several beetle species in pine. Formulations of this product provide up to two years of protection.

Engraver Beetles

Adult Ips attack smaller trees and tops of larger trees, but their preferred host material is fresh pine debris from construction, logging, firewood cutting, or blowdown. Living trees can be attacked and killed once populations have built up in fresh pine debris. Several generations are produced per year. Adults emerge from overwintering material and fly to find new hosts in spring. Blowdown material or fresh pine debris is preferred. Males initiate attacks and release chemicals which attract females. Adults build galleries (or tunnels) mate and lay eggs.

Galleries are distinctive. Typically there is a central nuptial chamber (an enlarged area) from which radiate several more or less linear adult galleries. Galleries slightly etch the sapwood, hence the common name, engraver beetle. Frequently three galleries originate from the nuptial chamber in the shape of a tuning fork. Adult galleries are open and not packed with boring dust. Larvae (immature beetles) feed in their own galleries perpendicular to the adult galleries for a few weeks before pupating (cocoon stage). Pupae turn into adults to complete the cycle. Evidence of attack includes fading foliage, red boring dust in bark crevices and occasionally small pitch tubes on trunks of live trees.

Prevention is the best way to reduce the chance of a successful attack. Trees infected with dwarf mistletoe or overcrowded are more susceptible so reducing disease and density is very effective. Avoid bringing infested pine firewood home. Splitting firewood and leaving it exposed to the sun will promote drying of the material which will reduce suitability to the beetle. Avoid construction damage to trees and leaving green, down trees on the site for long periods in spring.

In addition to those methods mentioned above, control can be achieved by covering infested material with clear, heavy plastic and placing it in the open. Bury edges with dirt. Brood will be killed by high temperatures. This method may not be effective if brood are nearly mature.

Dendroctonus Beetles

Western Pine Beetle:

The western pine beetle, Dendroctonus brevicomis, attacks trees of all sizes larger than 6 inches in diameter. However, large, old trees are attacked most commonly. Unlike the pine engraver beetles, this insect attacks living trees and rarely is found on pine debris. Best evidence of attack is the presence of pitch tubes (up to 1 inch in diameter) in the bark, often in bark crevices. Under the bark, galleries are mazelike and do not etch the wood (contrast with Ips).

Life cycle is quite similar to engraver beetles. All life stages are found in bark. Between two and four generations are produced per year. Flight and attacks start in late spring or early summer and continue until the onset of cold weather in fall. Attacks are initiated by adult females, usually at mid trunk. The infestation process is mediated by chemical messengers or pheromones released by the beetles in combination with host chemicals. Egg galleries are constructed by adults. They differ from Ips galleries in their shape and by the fact that they are packed with boring dust. Larvae feed in their own galleries perpendicular to the adult galleries. Later larval stages feed in the middle bark before pupating and eventually emerging. One generation requires between 2 and 10 months depending on temperature.

Prevention and control are described above. The main emphasis is on prevention. Removal of infested trees may provide some protection to surrounding trees, but these insects are very common, so removal of a few infested trees is not a guarantee of protection. Trees that are stressed by crowding, disease or human activities will remain susceptible unless some corrective action is taken.

Red Turpentine Beetle

The red turpentine beetle, Dendroctonus valens, is another bark beetle found in ponderosa pine. It is commonly seen in urban situations. It normally attacks injured, weakened or dying trees. Ordinarily it is not an aggressive bark beetle; however, sometimes through repeated attacks it kills trees. More often it weakens them, subjecting them to attack by other bark beetle species such as the engraver beetle or western pine beetle. The red turpentine beetle is the largest beetle in the group. The adult is distinctive because of its size, about 1/4", and reddish brown in color. Attacks are characterized by very large reddish pitch tubes at the point of entry. This species normally colonizes the lower part of the trunk and root crown.

CAUTION PESTICIDES: Please read

Specific chemical recommendations are given with caution. Whenever using chemical pesticides, always check the pesticide label to be certain its registered for use on the site to be treated. Chemical registrations and chemical use regulations frequently change. Contact manufacturers for the most current product information, including supplemental labeling and special local needs regulations. It is a violation of federal law to use any pesticide in a manner inconsistent with its labeling. Check with the Arizona Department of Agriculture, County Extension agents, state or federal forest health management specialists for current information on available insecticides. Trade names listed in these notes are given solely to provide specific information and are not intended as a recommendation, guarantee, or warranty of the product to the exclusion of others that may be suitable.

Chemical treatment for the indigenous bark beetles has never been shown to be effective, does not improve the general health of the forest and raises concerns regarding ground water pollution and human safety. Applying insecticide in the wild also kills wildlife.

For further information about these bark beetles, contact:

ARIZONA STATE LAND DEPARTMENT FORESTRY DIVISION(s):
3650 Lake Mary Road
Flagstaff, AZ 86001
520-774-1425

2901 West Pinnacle Peak Road
Phoenix, AZ 85027
602-255-4059

233 North Main Avenue
Tucson, AZ 85701
520-628-5480

809-C Gail Gardner Way
Prescott, AZ 86301
520-778-9567

HC 66 Box 57202
Pinetop, AZ 85935
520-367-0313

1616 West Adams
Phoenix, AZ 85007
602-542-2517

OR

USDA Forest Service
Southwestern Region
Southwest Forest Science Complex
2500 S. Pine Knoll Drive
Flagstaff, Arizona
520-556-2074

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