Conifer Bark Beetles Biology, Symptoms and Management FOREST HEALTH FACTSHEET Wisconsin Department of Natural Resources, Division of Forestry, Forest Health Program, Revised February 2021

LOCATIONS water table, wounds, fire, storm ark beetles are found through- damage and thinning during a Bout Wisconsin. Ranges vary drought. Bark beetles may also with each beetle species and its attack trees that are dying, freshly preferred host tree(s). Common cut trees, and logging debris. conifer bark beetle species include: Stressed trees are more vulnerable pine engraver (Ips pini), red tur- to bark beetle attack because their Left: An adult spruce beetle, Dendroctonus rufipennis. Photo: Edward H. Holsten, USDA Forest Service, Bugwood. pentine beetle (Dendroctonus defensive mechanisms are com- org • Right: An adult red turpentine beetle, Dendroctonus valens), chestnut-brown bark beetle promised. Healthy conifers pro- valens. Photo: Joseph Berger, Bugwood.org (Pityogenes hopkinsi), spruce beetle duce large quantities of pitch that (Dendroctonus rufipennis),eastern often prevents bark beetle attacks. larch beetle (Dendroctonus sim- Occasionally, extremely large plex), and balsam fir bark beetle populations of bark beetles are able (Pityokteines sparsus). to mass attack and overwhelm the defenses of healthy trees. IMPACT Many species of bark beetles attack BIOLOGY conifers in Wisconsin. Most prefer Adult beetles emerge in spring to attack only one or a few host after spending the winter in the species of conifers. Bark beetles layer of needles and other debris can attack trees under stress; stress on top of the soil or from an can be caused by overcrowding, infested tree. Beetles bore into drought, flood, damage from other a tree, mate and lay eggs. Fungi Red pine trees dying because of bark beetle feeding insects, disease, changes in the that may impact tree health are under the bark. Photo: Michael Hillstrom, Wisconsin DNR

An adult two-toothed pine beetle, Pityogenes bidentatus, Two Ips pini bark beetles in a gallery. Photo: Linda Williams, Wisconsin DNR gallery. Photo: Michael Hillstrom, Wisconsin DNR sometimes introduced during col- MANAGEMENT onization. Larvae hatch and feed Management strategies will vary beneath the bark creating galleries depending on the bark beetle that disrupt the flow of water and species, host species, and site nutrients in the tree. Some species, conditions. Recommendations for such as the pine engraver (Ips pini) managing conifer bark beetles may complete development rapidly (in include: as little as 30 days) and go through • If trees are stressed from drought, multiple generations per year. storm damage, or disease consid- Numerous tiny bark beetle exit holes. Photo: Michael Other species, including the spruce Hillstrom, Wisconsin DNR er a pre-salvage harvest. beetle (Dendroctonus rufipennis), • Promptly salvage trees that are take up to two years to complete severely damaged by storms, fire, their life cycle. Warmer tempera- disease, insects, or other destruc- tures allow beetles to develop more tive agents before bark beetles quickly whereas cooler weather have a chance to infest them. will lengthen the cycle. Popula- • Harvest conifers during winter or tions of bark beetles can build up when bark beetles are not active. rapidly in hot, dry years. Remove cut logs and tops down to 2 inches in diameter from the SIGNS AND SYMPTOMS site by March if cut during the • Individual or groups of trees with winter, or within three weeks of Pitch tube resulting from attack by a red turpentine light green, straw yellow, red beetle, Dendroctonus valens. Photo: Michael Hillstrom, being cut from March through Wisconsin DNR or brown foliage. Brown, dead August. needles and tree mortality may • Logging debris remaining on the occur abruptly. site should be left attached to the • Small, round exit holes in the main stem, scattered into open- bark or pitch tubes near the base ings, or driven over to break it up of the tree. and allow faster drying. • Feeding galleries (tunnels) under • Minimize damage to remaining the bark. trees during logging operations. • Fine dust in bark crevices, at the Avoid large wounds, soil com- base of the tree, or on understory paction and root injury which plants. can stress trees and attract bark beetles. PREVENTION • Plant site-appropriate conifer Conduct sustainable forest man- species, taking into consideration Woodpeckers remove bark from beetle infested trees to agement activities such as thinning soil types and other factors that eat the larvae hiding beneath. Photo: Brian Schwingle, stands at the proper time to main- impact tree health and survival. Minnesota DNR tain healthy, vigorous trees. Avoid stressing conifers in multiple ways, such as thinning during a drought,

whenever possible. Remove har- Printed on vested logs within three weeks of recycled paper. being cut during the months of Wisconsin Department of Natural Resources March through August. PO Box 7921, Madison, WI 53707-7921 PUB-FR-622c 2021 The Wisconsin Department of Natural Resources provides equal oppor- tunity in its employment, programs, services and functions under an Affirmative Action Plan. If you have any questions, please write to Equal Opportunity Office, Department of Interior, Washington, DC 20240. Remove harvested pine logs within three weeks from This publication is available in alternative format (large print, Braille, audio tape, etc.) upon request. Please call the Department of Natural March through August to prevent bark beetle infesta- Resources Accessibility Coordinator at 608-267-7694 for more tions. Photo: Michael Hillstrom, Wisconsin DNR information.

For more information visit dnr.wi.gov, keyword “bark beetle.”