****Forest Insect & Disease Leaflet 127**U. S. Department of								Agriculture Forest ServiceForestServiceThe Spruce Beetle E.H. Holsten1, R.W. Thier2, A.S.				  Munson3, and K.E. Gibson41 Entomologist, U.S. Department of				Agriculture, Forest Service, Anchorage, AK.2 Entomologist, U.S.				Department of Agriculture, Forest Service, Boise, ID. 3				Entomologist, U.S. Department of Agriculture, Forest Service, Ogden, UT.				4 Entomologist, U.S. Department of Agriculture, Forest Service,				Missoula, MT. The spruce beetle,				*Dendroctonus rufipennis* (Kirby), is the most significant natural				mortality agent of mature spruce. Outbreaks of this beetle have caused				extensive spruce mortality from Alaska to Arizona and have occurred in every				forest with substantial spruce stands. Spruce beetle damage results in the loss				of 333 to 500 million board feet of spruce saw timber annually. More than 2.3				million acres of spruce forests have been infested in Alaska in the last 7				seven years with an estimated 30 million trees killed per year at the peak of				the outbreak. In the 1990's, spruce beetle outbreaks in Utah infested more than				122,000 acres and killed more than 3,000,000 spruce trees. In the past 25				years, outbreaks have resulted in estimated losses of more than 25 million				board feet in Montana, 31 million in Idaho, over 100 million in Arizona, 2				billion in Alaska, and 3 billion in British Columbia (fig. 1). Spruce				beetle outbreaks cause extensive tree mortality and modify stand structure by				reducing the average tree diameter, height, and stand density. Residual trees				are often slow-growing small and intermediate-sized trees which eventually				become dominant. Spruce beetle outbreaks can affect non-timber				resources as well. For example, as mature spruce are killed, forage may				increase, benefiting some wildlife species. But species that depend on mature				spruce or clumps of spruce to meet habitat requirements may be adversely				affected. There has been a significant change in fuel type and an increase in				large woody debris accumulating on the forest floor following spruce beetle				outbreaks in Alaska. Uncharacteristic, stand-replacing fires occurred in				central Idaho spruce stands following ten years of spruce beetle outbreaks.				Extensive spruce mortality can also affect water yields resulting in water				increases in rivers, lakes, and streams because of reduced transpiration from				dead and dying trees. Scenic quality may also be diminished throughout affected				landscapes. **Hosts** The spruce beetle infests all				species of spruce within its geographical range (fig. 2). The more important				commercial species of spruce attacked include white (*Picea glauca*				[Moench] Voss), Lutz (*P. X lutzii Little), Sitka (*P. sitchensis*				[Bong.] Carr.), and Engelmann (*P. engelmannii* Parry ex Engelm.).***Evidence of				Infestation** On standing trees, the first sign of spruce beetle				infestation is reddish-brown boring dust accumulating at the beetle's entrance				holes, in bark crevices, and on the ground around the trunk of infested trees.				Masses of pitch may accumulate around the entrance sites. These signs are most				visible during the summer of attack and become less noticeable the following				season.  On windthrown trees and logging residuals, spruce beetle				attacks are readily detected on the lower surfaces of the material and should				not be confused with engraver beetle (*Ips* spp.) attacks more commonly				found on the upper surfaces.				Some standing trees				may be attacked on only one side of the bole, creating a "strip attack. " The				infested area may die, but the tree usually remains alive, so the foliage does				not discolor. Trees with "strip attacks" frequently are infested by subsequent				spruce beetle generations and may host two or more generations simultaneously.				 During the first fall and winter following spruce beetle infestation,				look for trees "debarked" by woodpeckers (fig. 3). Partially debarked, green				trees are easily noticed. However, on trees without significant debarking, one				must be relatively close to see sawdust in bark crevices and around the tree				base. The needles of infested trees do not usually fade or discolor				within the first year following attack. However, during the second summer, most				needles turn yellowish-green or orange-red (Alaska). Some even remain green				until the third summer, or up to 2 years after the initial infestation. The				needles on separate branches of the same tree discolor at different times.				Needles on infested trees commonly drop to the ground as a result of wind or				thunderstorms the second summer after the tree was attacked, leaving the upper				crowns of exposed twigs with a yellowish-orange to reddish hue later turning to				grey. **Identification of				the Life Stages**Adult beetles are dark brown to black with				reddish-brown or black wing covers. The beetles are cylindrical, approximately				1/4 inch (6 mm) long, and 1/8 inch (3 mm) wide (fig. 4).  Spruce beetles				are similar to other *Dendroctonus* beetles and, if no host material is				present, can only be distinguished by microscopic examination. At first glance,				spruce beetles may also be confused with *Ips* beetles in spruce. It is				important to remember that the posterior margins of the wing covers on spruce				beetles are evenly rounded, while *Ips* beetles have concave margins with				teeth like projections.  The eggs of the spruce beetle are oblong,				pearly white, and 1/16 inch (1.5 mm) long. The cream colored larvae are stout,				cylindrical, legless grubs that pass through four larval stages (instars) and				reach a length of l/4 inch (6 mm) at maturity. The pupae are opaque white,				inactive, and somewhat similar in size and shape to adults.**Life Cycle**				Spruce beetles may complete their life cycle in 1 year on warm sites at lower				elevations or take up to 3 years in cool, well-shaded locations on north				slopes.  However, throughout most of its range and in most seasons, two				years are generally required for the spruce beetle to complete its life cycle.				Although adults may emerge any time from May to October, depending on				temperature, most attacks occur in early summer. Adult beetles attack host				material soon after emerging. Adults that appear in August to October may				represent a re-emergence of parent adults or a movement of maturing brood				adults to hibernation sites.  To deposit eggs, females bore through the				outer bark of host trees and create egg galleries in the underlying phloem				tissue. Eggs are laid on either side of the egg gallery (fig. 5). Egg galleries				are slightly wider than the beetle and, except for the terminal portion, are				packed with frass and boring dust. Egg gallery length ranges from about 2.5 to				12 inches (6 to 13 cm) (fig. 6). Eggs are usually deposited in short rows along				alternate sides of the gallery in numbers ranging from 4 to 14 eggs per				centimeter of gallery. Most of the eggs hatch by August. The larvae				bore outward from the egg gallery and feed as a group for the first and second				instars. Third and fourth instars construct individual feeding galleries. The				larval stage predominates during the first winter, although parent adults and				eggs may also be present. During the 2-year life cycle, most larvae pupate				approximately 1 year after attack. Pupation lasts 10 to 15 days and usually takes place in pupal				chambers at the end of larval galleries. During the second winter of				the 2-year cycle in standing trees, some beetles overwinter in their pupal				sites, others emerge, move to the base of the tree, and bore into the bark near				the litter line to hibernate. During the second winter of the 2-year life cycle				in standing trees, some beetles overwinter in their pupal sites but the				majority, often as high as 95 percent, of the new adults emerge, move to the				base of the tree, and bore into the bark near the litter line to overwinter.				Overwintering at the base of the infested tree reduces predation by woodpeckers				and reduces winter mortality due to extreme cold temperatures. In windthrown				trees, most adults overwinter in place.  Approximately 2 years after				attack, adults emerge from overwintering sites and attack new host material.				**Stand Conditions Conducive To				Infestations** Endemic spruce beetle populations usually live in				windthrown trees (fig. 7). When populations increase to high levels in downed				trees, beetles may enter susceptible, large-diameter standing trees. Most				outbreaks in standing timber originate in windthrown trees.In mature stands, larger				diameter (> or = 18") trees usually are attacked first, an obvious				characteristic denoting susceptibility to spruce beetle attack. If an				infestation persists in a stand, smaller diameter trees are attacked. Recent				evidence from Alaska indicates that tree diameter is important in determining				susceptibility only when coupled with less-than-average radial growth in the				preceding five years.In the Rocky Mountain area, susceptibility, or				hazard, of a stand to spruce beetle attack is based on the physiographic				location, tree diameter, basal area, and percentage of spruce in the canopy.				Spruce stands are highly susceptible if they grow on well-drained sites in				creek bottoms, have an average diameter-at breast-height (dbh) of 16 inches or				more, have a basal area greater than 150 square feet per acre, and have more				than 65 percent spruce in the canopy. In Alaska, susceptibility of				spruce stand is based on average tree diameter, age of stand, condition of the				stand, and proportion of spruce in the canopy. A spruce stand of old-growth or				damaged larger host trees is very susceptible to spruce beetle attack				particularly if larger diameter spruce trees have a slower-than-average growth				rate, have an average dbh greater than 12 inches, and if the stand has more				than 70 percent spruce. Susceptibility of a spruce stand to spruce				beetle attack in British Columbia and the Northeastern United States is based				on criteria similar to that used in the Rocky Mountains and Alaska.				Hazard and risk (= probability of an outbreak) rating systems based on the				stand and site conditions discussed above have been developed which enable				managers to identify stand susceptibility to spruce beetle attack.				**Management Strategies**				Forest managers can develop various strategies to avoid or reduce resource				losses to spruce beetles. Before developing a strategy, the forest manager must				evaluate resource values and economics of management actions for each stand				combined with overall management objectives. The beetle population level must				also be considered because population levels will determine the priority of				management actions and the type of strategy to be invoked. A principal				strategy that should be considered for susceptible sites would consist of				silvicultural treatments of moderate-high hazard stands that result in				maintaining their health with a moderate growth rate. The first step in this				strategy is to hazard-rate spruce stands, which will designate the most				susceptible stands. Moderate-high hazard stands can then be treated using				silvicultural strategies that reduce stand susceptibility. Infested logging				residuals will not become a significant contributor to spruce beetle				populations if stump height is kept below 18 inches (45 cm) and cull logs and				tops are limbed, cut into short lengths, and left unshaded, unpiled, and				exposed to sunlight. Silvicultural treatments have greater long-term				effectiveness, because treatments modify stand conditions that contribute to				spruce beetle population increases.**Silvicultural** strategies may				be more effective if beetle populations are not immediately threatening				resource values. If beetle populations are threatening, then strategies that				include suppression methods are more appropriate. Suppression methods,				including silvicultural, physical (fire & solar heat), and chemical				measures, are available to forest managers for reducing spruce beetle				populations. Some methods are suitable only for populations in windthrown host				material; other methods are better suited for infestations in standing trees.				Most suppression methods are short-term responses to existing beetle				populations and, therefore, address only an immediate need.**Silvicultural Methods****Sanitation				overstory removal** - Removal of all infested and susceptible spruce to				encourage regeneration of a new vigorous stand. Sanitation partial cut includes				the removal of infested and susceptible spruce to improve the growth of the				residual stand. Sanitation partial cut removes most of the larger trees but may				leave a residual stand that is below the recommended level of basal area. This				residual stand may be more susceptible to windthrow. Pruning the lower 1/3 of				the live crown of smaller diameter trees significantly reduces the				susceptibility of spruce to beetle attack in Alaska.**Trap trees** are green trees with a dbh greater than 12				inches that are felled before beetle flight. Trap trees can absorb up to 10				times the number of spruce beetles that a standing tree will absorb. Once				infested, trap trees **must** be removed. Trap trees shaded from				direct sunlight attract the most beetles. Spruce beetles attack cool, shaded				portions of the trap tree boles (fig. 8). Felled trees should not be delimbed.				Limbs on the upper side of the bole provide shade while limbs on the underside				permit the beetles to colonize the underside of the bole by keeping it off the				ground. Past ratios of trap trees to				infested standing trees have ranged from 1:2 to 1:10. Current ratios vary with				the size of the green trees to be felled as traps compared to the number and				size of infested trees and the existing beetle population.**Physical Methods****Solar				heat** involves exposing infested logging residuals or windthrow to direct				sunlight to kill inhabiting larvae. To maximize brood mortality, all host				material greater than eight inches dbh should be cut into 5-foot lengths. All				branches and debris shading the host material should be removed. The infested				material should be rotated at 2- week intervals during the summer to expose all				surfaces. While using solar heat is effective on some sites in the Rocky				Mountains, it is not effective in Alaska, because summer temperatures are not				warm enough. Fire involves piling and burning infested logging				residuals and windthrow to destroy inhabiting broods. The infested material is				usually green and difficult to burn, but only the bark has to be burned to				destroy the inhabiting brood. **Chemical Methods****Pheromones** are				chemical substances, produced by insects, that influence their behavior.				Synthetic aggregating and anti-aggregating pheromones increase attractiveness				of trap trees, attract beetles into trees to be cut, or discourage infestation				of high-value trees. Aggregating pheromones are effectively used with trap				trees. Under some circumstances, aggregating pheromones have also been used				successfully in catchment traps to reduce small, isolated beetle populations.				**Insecticides**, such as carbaryl and pyrethroids, can be				applied to the boles of uninfested trees to kill attacking adults. In Alaska,				carbaryl applied as a 2-percent spray has provided 100 percent protection from				attacking beetles for at least 2 years.**Assistance** More information about the				management of the spruce beetle may be obtained from the State Forester's				office or the U.S. Department of Agriculture, Forest Service, Forest Health				Protection. The publications listed in the references provide more				information on the biology, ecology, and management of the spruce				beetle.**References** Alexander, R.R. 1986.				Silvicultural systems and cutting methods for old-growth spruce-fir forests in				the central and southern Rocky Mountains. Gen. Tech. Rep. RM-126. USDA Forest				Serv., Rocky Mtn. Forest & Range Exp. Sta., Ft. Collins, CO. 33 p.				British Columbia Ministry of Forests. 1981. Spruce beetle management seminar				and workshop. In: Proceedings, 1980 seminar and workshop; 1980 October 7-8;				Prince George, B.C. Pest Mgmt. Rep. No. 1, Province of British Columbia,				Ministry of Forests, Victoria, B.C., Canada. 16 p. Gibson, K.E. 1984.				Use of trap trees for the reduction of spruce beetle-caused mortality in				old-growth Engelmann spruce stands in the Northern Region. Rep. No. 84-10. USDA				Forest Serv., Northern Region, Missoula, MT. 11 p. Hard, J.S.; Holsten,				E.H. 1985. Managing white and Lutz spruce stands in south central Alaska for				increased resistance to spruce beetle. Gen. Tech. Rep. PNW-188. USDA Forest				Serv., Pacific NW Forest & Range Exp. Sta., Portland, OR. 21 p.				Hard, J.S.; Werner, R.A.; Holsten, E.H. 1983. Susceptibility of white spruce to				attack by spruce beetles during the early years of an outbreak in Alaska. Can.				J. For. Res. 13:678-684. Hodgkinson, R.S. 1985. Use of trap trees for				spruce beetle management in British Columbia: 1979-1984. Pest Mgmt. Rep. No.				5., Province of British Columbia, Ministry of Forests, Victoria, B.C., Canada.				39 p. Holsten, E.H. 1990. Spruce beetle activity in Alaska: 1920-1989.				Tech. Rep. R10-90-18. USDA Forest Serv., Alaska Region, Anchorage, AK. 28				p. Holsten, E.H.; Werner, R.A.; DeVelice, R.L. 1995. Effects of a				spruce beetle (Coleoptera: Scolytidae) outbreak and fire on Lutz spruce in				Alaska. Environ. Entomol. 88(6):1539-1547. Johnson, K.J. 1996.				Effectiveness of carbaryl and pyrethroid insecticides for protection of				Englemann spruce from attack by spruce beetles (Coleoptera: Scolytidae). MS				Thesis. Utah State Univ., Logan, UT. 87p. Massey, C.L.; Wygant, N.D.				1954. Biology and control of the Engelmann spruce beetle in Colorado. Agric.				Cir. No. 944. USDA, Washington, D.C. 35 p. Reynolds, K.M.; E.H.				Holsten. 1994. Estimating priorities of risk factors for spruce beetle				outbreaks. Can. J. For. Res. 24:3027-3033. Reynolds, K.M.; E.H.				Holsten. 1996. Classification of spruce beetle hazard in Lutz and Sitka spruce				stands on the Kenai Peninsula, Alaska. For. Ecology and Management.				84:251-262. Reynolds, K.M.; E.H. Holsten. 1997. SBexpert user guide				(version 2.0): A knowledge-based decision-support system for spruce beetle				management. Gen. Tech. Rep., PNW-GTR-401. USDA Forest Serv., Pacific NW Forest				& Range Exp. Sta., Portland, OR. 62p. Schmid, J.M.; Frye, R.H.				1976. Stand ratings for spruce beetles. Res. Note RM-309. USDA Forest Serv.,				Rocky Mtn. Forest & Range Exp. Sta., Ft. Collins, CO. 4 p. Schmid,				J.M.; Frye, R.H. 1977. Spruce beetle in the Rockies. Gen. Tech. Rep. RM-49.				USDA Forest Serv., Rocky Mtn. Forest & Range Exp. Sta., Ft. Collins, CO. 38				p. Thier, R.W. 1994. Chronology of the current spruce beetle				infestation on the Payette National Forest, Idaho. Rep. R4-94-02. USDA Forest				Serv., Intermountain Region, Ogden, UT. 23p. Werner, R.A.; Baker, B.H.;				Rush, P.A. 1977. The spruce beetle in white spruce forests of Alaska. Gen.				Tech. Rep. PNW-61. USDA Forest Serv., Pacific NW Forest & Range Exp. Sta.,				Portland, OR. 13 p. Werner, R.A.; Hastings, F.L.; Holsten, E.H.; Jones,				A.S. 1986. Carbaryl and lindane protect white spruce from attack by spruce				beetles (Coleoptera: Scolytidae) for three growing seasons. J. Econ. Entomol.				79:1121-1124. Wood, S.L. 1963. A revision of the bark beetle genus				Dendroctonus Erichson (Coleoptera: Scolytidae). The Great Basin Naturalist.				23:1-117. Pesticides used improperly can be injurious to human				beings, animals, and plants. Follow the directions and heed all precautions on				labels. Store pesticides in original containers under lock and key out of the				reach of children and animals -- and away from food and feed. Apply				pesticides so that they do not endanger humans, livestock, crops, beneficial				insects, fish, and wildlife. Do not apply pesticides where there is danger of				drift when honey bees or other pollinating insects are visiting plants, or in				ways that may contaminate water or leave illegal residues. Avoid prolonged				inhalation of pesticide sprays or dusts: wear protective clothing and				equipment, if specified on the label. If your hands become contaminated with a				pesticide, do not eat or drink until you have washed. In case a pesticide is				swallowed or gets in the eyes, follow the first aid treatment given on the				label, and get prompt medical attention. If a pesticide is spilled on your skin				or clothing, remove clothing immediately and wash skin				thoroughly.**NOTE:** Some States have restrictions on the use of				certain pesticides. Check your State and local regulations. Also, because				registrations of pesticides are under constant review by the U.S. Environmental				Protection Agency, consult your local forest pathologist, county agriculture				agent, or State extension specialist to be sure the intended use is still				registered. **NOTE:** Registration of pesticides are under constant review				by the Federal Protection Agency. Use only pesticides that bear the EPA				registration number and carry appropriate directions.  Revised November 1999 Formatted for the Internet March 2000				 Return to the				Forest and Tree Health				Publications**