The Northern Spruce Engraver: Ips perturbatus
Ips beetles, or more commonly referred to as engraver beetles, are one of the most commonly encountered bark beetles of coniferous trees. More information has been written about this group of bark beetles than any other genus of Scolytidae (family of bark beetles) except possibly Dendroctonus. Most species of Ips breed in slash, broken, fallen, or dying conifers. Some species, however, are capable of attacking, killing, and breeding in healthy trees. To date, the spruce beetle, Dendroctonus rufipennis, is the most important insect pest of Alaska's spruce stands. More than 2.3 million acres of Alaska spruce forests have been infested in the last ten years. There is a wealth of information about the spruce beetle in Alaska and most is available from the Sbexpert System (http://www.fsl.orst.edu/usfs/sbexpert/): A knowledge-based decision-support system for spruce beetle management. Ips beetles, although commonly encountered in Alaska's boreal forests, have seldom been considered a "problem". In recent years, however, there has been a noticeable increase in tree killing by Ips beetles in interior and south-central Alaska's white and Lutz spruce forests. The engraver species most commonly associated with this tree killing is the northern spruce engraver, Ips perturbatus. This "increase" in I. perturbatus activity is thought to be a reflection of increased spruce beetle-caused tree mortality, increased forest management, and the increase in mean annual temperature which has been occurring for at least 80 years in south-central and interior Alaska.
The following is an "electronic" textbook which provides background information on the biology, ecology, and management of Ips perturbatus. There is also an annotated reference section of the most pertinent Ips information. Subject matter of this hypermedia textbook is displayed by selecting a chapter and section to view. Within chapter sections, expanded discussions on selected topics, literature references, and graphic illustrations are accessed by selecting hypertexts or links.
Ips perturbatus Textbook
Chapter List:
Additional information pertaining to I. perturbatus or other Alaska Forest Health Issues can be obtained from the following links:
USDA Forest Service, Alaska Region Forest Health Highlights(http://www.fs.fed.us/r10/spf/fhp/fhpr10.htm)
State of Alaska DNR Forest Health Information(http://www.dnr.state.ak.us/forestry/insects.htm)
For specific information concerning this textbook; please contact:
Jim Kruse jkruse@fs.fed.usINTRODUCTION
ROLE OF INSECTS AS DISTURBANCE AGENTS
HOSTS
INTRODUCTION - Role of Insects as Disturbance Agents
A key premise of ecosystem management is that native species have adapted to, and in part, evolved with natural disturbance events. Species loss and ecosystem change have been observed in areas where "natural" disturbance regimes have been substantially altered. Disturbances, large and small, are responsible for the way current landscapes appear and function today. Disturbances of various kinds and intensities will determine the structure, composition, and function of future landscapes. The vegetation of forest ecosystems is best thought of as a mosaic, frequently changing and being redefined, not as a uniform, stable cover. Alaska ecosystems are shaped/produced by disturbances. Just note the effects of glaciation, earthquakes, tidal waves, fire, wind, flooding, etc. Disturbance events such as fire and insect and disease outbreaks create and maintain a shifting mosaic of landscape patterns. Both fire and flooding are responsible for spruce and birch regeneration in south-central and interior Alaska; windthrow is important in southeast Alaska.
Alaska insect communities, probably one of the largest components of forest ecosystems, are also "creatures" of disturbance as well as agents of disturbance. Arctic/boreal insect communities are characterized by having few species and large population numbers. These insects are opportunistic in their behaviors. They respond quickly to disturbances in climate, food, and breeding material.
Bark beetles, such as the spruce and engraver beetle, respond quickly to large scale blowdown, fire scorched trees, snow and ice breakage, or spruce impacted by flooding; all of which provide both food and breeding habitat. Large bark beetle populations can be produced by such breeding material, leading to outbreaks.
As agents of disturbance, bark beetles are one of the most important mortality agents of spruce stands in Alaska. At low, stable population levels, small isolated patches of dead trees appear throughout the mixed forest landscape creating habitat for cavity nesting birds such as woodpeckers and golden-eye ducks. That is, the effects of the disturbance are kept to a minimum due to the variety of tree species (birch, spruce, aspen) in the affected area. On the other hand, enormous bark beetle outbreaks, such as those of the spruce beetle, are occurring in many of south-central Alaska's uniform, extensive spruce forests. More than 2.3 million acres of spruce forests have been infested in the last ten years. 90% of the spruce overstory in many areas of south-central Alaska has been killed in less than five years.
Boreal and arctic plant and animal communities are regulated with respect to their ranges, population sizes, etc. by climatic factors such as temperature and precipitation. There is a strong indication that Alaska has significantly warmed in the last 80 years or more and this warming trend may be the most significant in thousands of years (Juday, Pers. Comm. 1997). The current spruce beetle epidemic, which is both intensive as well as extensive, is thought to have been brought about, in part, by a recent warming trend. Increased temperature can "benefit" bark beetles in a number of ways: (1) Spring weather is earlier and warmer thereby increasing water stress to spruce; (2) Emerging bark beetles are dispersed sooner and for a longer time because of the warmer temperatures; and most importantly in the case of the spruce beetle, (3) The normal 2-yr life cycle, under warmer temperatures, is condensed into 1-yr. In essence, the beetle population doubles every year! This same scenario (e.g. warming trend) can or is affecting other boreal forest insects such as the spruce budworm, larch sawfly, and the northern spruce engraver. As previously mentioned, insect outbreaks are major disturbance factors in Alaska's boreal forests. If global warming occurs (and there is more than ample evidence that it has), the disturbance patterns of forested ecosystems caused by insects may significantly change (Fleming and Candau 1998).
There are a variety of impacts (changes) associated with bark beetle outbreaks, both timber and non-timber, to forest resources. The short term impacts are socio-economic in nature and can be viewed positively or negatively. In the long term, these changes are neither positive or negative and are biological or ecological in nature.
INTRODUCTION - Hosts
The genus Ips is distributed throughout most of the coniferous forests world-wide. More than 60 species have been assigned to the genus of which 25 occur in North America (Wood_1982). All North American species of Ips attack coniferous trees of the genera Picea and Pinus (spruce and pines, respectively). The distribution of I. perturbatus is transcontinental in Canada; northern United States including Alaska. Hosts include Picea spp.; also Pinus banksiana and P. contorta (Wood_1982, Bright_1976). In Alaska, I. perturbatus is commonly encountered in south-central and interior Alaska attacking and breeding in white (Picea glauca) and Lutz (P. glauca X lutzii) spruce. Rarely are black (P. mariana) or Sitka (P. sitchensis) spruce attacked.
Lutz Spruce
Hybrids between white (Picea glauca) and Sitka spruce (P. sitchensis) were first reported by Little (Little_1953) and named P. X lutzii. Such hybridization has been found in British Columbia (Daubenmore_1968) as well as the Kenai Peninsula in south-central Alaska (Copes & Beckwith_1977). Much of the west side of the Kenai Peninsula appears to be a hybrid swarm area with stands containing both Sitka and white spruce genes.
AESTHETICS
TIMBER
POTENTIAL FOR WILDFIRE
UNDERSTORY VEGETATION
WILDLIFE HABITAT
RESOURCE IMPACTS - Aesthetics
To date, the majority of the northern spruce engraver beetle outbreaks have occurred in remote areas of Alaska's interior white spruce forests. Consequently, most of these outbreaks have gone "un-noticed". However, engraver outbreaks have recently occurred along the Seward Highway (a National Scenic By-way) on the Kenai Peninsula in south-central Alaska (Holsten 1996, 1997, 1998). This outbreak and the associated standing dead trees have been noticed by passing motorists. If engraver outbreaks become more common in south-central Alaska, the effects may detract from the scenic quality of the landscape much in the same way as the on-going spruce beetle outbreaks.
A USDA Forest Service sponsored survey of residents and visitors to the Kenai Peninsula, Alaska in the summer of 1990 revealed several consistent patterns of perceptual and attitudinal responses to the on-going spruce bark beetle outbreak in the area. Residents and visitors consistently rated forest vistas damaged by bark beetles lower in scenic beauty, and the more tree mortality present the lower the perceived scenic beauty (Daniel_and_Orland_1991). Both residents and visitors cite loss of scenic values as an important effect of the beetle damage, and visitors consistently report site-seeing as a dominant activity, and indicate viewing mountains, forests, and coast lines as major factors affecting the quality of their visit to Alaska.
When viewed from the foreground, effects of the beetle infestation include numerous fallen-over trees, dead standing trees, and areas where trees have been removed, leaving low stumps. These effects have the most negative impact in the campgrounds where the loss of a "visual canopy" and screening between sites are detrimental to the campers' experience. These effects also impact the recreation experience along the trails, although not to as great a degree, since the hiker is not stationary. The fallen trees and wide-open feeling is most noticeable in early spring, before grass, tall forbs, and brush leaf-out.
RESOURCE IMPACTS - Timber
Alaska engraver outbreaks in standing healthy trees have been sporadic and of short duration (Holsten and Werner_1987). In most years, endemic engraver populations infest widely scattered individual trees or small groups of trees (Werner_1988).Extensive engraver outbreaks, however, have been recorded in Alaska (Holsten_1986). In the 1950's, one such outbreak covered more than 1,500 sq. miles and thousands of mature, saw-log white spruce were killed (Downing_1957). In 1986, engraver beetles killed thousands of mature white spruce on more than 16,000 acres near Fairbanks following a wildfire and a winter with extensive ice and snow breakage. There are no data with respect to volume of timber "lost" in these outbreaks.
For the most part, engraver activity is most commonly associated with slash and small diameter standing trees. Consequently, there normally is no loss of commercial timber. Stand structure and composition, however, can be dramatically altered as the smaller spruce are "removed" through Ips activity. For example, a northern spruce engraver outbreak in the Granite Creek area of the Kenai Peninsula, south-central Alaska, killed approximately 50% of the residual, small diameter Lutz spruce immediately after a sanitation/salvage timber harvest (Holsten_1998).
Sap rot and weather check are probably the forms of deterioration that are associated with engraver-killed trees. These forms of deterioration are commonly associated with spruce beetle-killed trees and occur within three years of tree death (Lowell and Willits_1998). Weather check of engraver-killed spruce may occur quicker than spruce beetle-killed spruce. Most engraver activity occurs in Alaska's interior continental climate which is warmer and drier than the transitional-maritime climate where most spruce beetle outbreaks occur. With respect to pulpability of engraver-killed spruce, live and dead spruce can probably be pulped effectively with the kraft pulping process similar to spruce beetle-killed spruce (Werner et al._1983, Scott et al. 1996).
RESOURCE IMPACTS - Potential for Wildfire
Vegetation changes associated with engraver beetle-killed spruce will alter surface fuel conditions, resulting in increased fire hazard. Surface fuels change from shaded forest litter or litter and grass under a spruce forest canopy (low hazard fuel types) to grass and shrubs in combination with large accumulations of dead woody material (high hazard fuel types). As fuel conditions change over time, fire hazard increases because potential fire behavior changes from one of a low intensity, slow moving, easier to control fire, to one of a high intensity, fast moving, and difficult to control fire.
In Alaska, there is concern that fire hazard of spruce beetle impacted stands will increase over time as dead fuels fall and dry grass accumulates, thus increasing fuel loading. After an outbreak, grass cover in impacted stands increases from less than 5% to more than 50%. Blue-joint grass cover provides a fine flashy fuel; fire spreads rapidly through this grass because of large volumes of fine dry litter present in the spring. Also, recent Alaska studies (Schulz_1995) have shown that more than 35 tons per acre of large woody debris accumulates on the forest floor 5-10 years after a spruce beetle outbreak. In contrast, approximately 2 tons per acre of large woody debris accumulates in uninfested stands. Sound wood, which makes up 65% of the total fuel tonnage, is the heaviest component of the fuels complex. They do not readily ignite, but once ignited they burn at higher temperatures for longer periods.
Comparable studies with respect to changes in the fuel complex associated with engraver outbreaks, however, have not been undertaken. It is believed, that such changes will be significantly less than those associated with spruce beetle outbreaks. This belief is based on: (1) The significant increase of blue-joint grass seen in many spruce beetle impacted sites probably will not occur in engraver impacted spruce stands. Blue-joint grass is more prevalent in south-central Alaska's moister climate; less so in interior Alaska's drier climate; (2) Most engraver outbreaks subside quickly (within 3 years) resulting in significantly less spruce mortality than that associated with spruce beetle outbreaks. Thus, amounts of large woody debris should be significantly less in engraver impacted stands; and (3) There appears to be less heart rot in interior white spruce than found in south-central Alaska's Lutz spruce stands. Thus, stem breakage of engraver killed-spruce should be less than spruce beetle-killed Lutz spruce.
RESOURCE IMPACTS - Understory Vegetation
From the results of studies conducted elsewhere, (Stone_and_Wolfe_1996) we can expect that with 50-70% canopy "removal" (e.g. bark beetle killed trees), diversity of understory vegetation may increase. With 80-100% canopy removal, diversity may be expected to decrease. The response of understory plant species diversity to increasing disturbance severity is consistent with the pattern predicted by the intermediate disturbance hypothesis (Connell_1978).
A recent study (Holsten_and_others_1995) has indicated a reduction in species richness in heavily spruce beetle-effected areas. This reduction in plant diversity (a significant reduction in "shade-loving" species) was probably a result of the significant increase, and competitive advantage, of blue-joint grass and fireweed. With respect to engraver outbreaks, diversity of understory vegetation probably will increase as engraver outbreaks seldom are of the same intensity and duration as spruce beetle outbreaks.
RESOURCE IMPACTS - Wildlife Habitat
The effects of an engraver beetle outbreak on each wildlife species depends on the species' requirements and the intensity and extensiveness of the infestation. If only a few trees are infested on 1-2 acres (<1 ha), as would be expected with most engraver populations, changes could be insignificant. If the outbreak reaches the intensity and extensiveness of many of the spruce beetle outbreaks on the Kenai Peninsula, then significant changes could be expected. For example, populations of those Alaskan wildlife species that are dependent upon live, mature spruce stands for habitat requirements could decline such as Townsend warblers, Ruby-crowned Kinglets, spruce grouse, red and flying squirrels.(Lance_And_Howell_2000)
Similar to the previous discussion on effects of understory vegetation (Stone_and_Wolfe_1996) we can expect that with 50-70% canopy removal wildlife diversity may increase. With 80-100% canopy removal, wildlife diversity may be expected to decrease. Since trends in mammal and bird populations have not been adequately studied, much of the expected changes could be developed from expert opinions based on knowledge of the animals' requirements. Established wildlife-habitat relationships may be used to predict expected response(s) of individual wildlife species to habitat changes associated with engraver beetle outbreaks.
EVIDENCE OF INFESTATION - Bole Infestation
On standing trees, the first sign of engraver 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 (Figure: 1) (Holsten and Werner_1987). Boring dust is commonly found in distinct piles marking the location of individual beetle attacks on logging slash or windthrow. On windthrown trees and in log decks, spruce beetle attacks are readily detected on the lower surfaces of logs and should not be confused with Ips beetle attacks that are more commonly found on the upper surfaces. "Pitch-outs", or unsuccessful attacks, are rarely encountered with engraver attacks. The presence of pitch-outs is more commonly associated with spruce beetle attacks.
During the first fall and winter following engraver infestation, one should look for trees "debarked" by woodpeckers (Figure: 2). Partially debarked trees are easily noticed during the winter.
EVIDENCE OF INFESTATION - Foliage Color Change
A change in foliage color is another indication of engraver beetle attack on standing spruce. Needles begin to fade from dark green to pale yellowish-green to red as early as 1 month after attack in interior Alaska (Figure 3). By the end of the first summer after attack, most foliage has faded and most needles have dropped. In succeeding years, engraver killed-spruce appear silver-gray and may remain that way for many years (Holsten and Werner_1987). The rapidity of color change of engraver killed trees is in contrast to the color change of spruce beetle-killed trees. The needles of spruce beetle infested trees do not usually fade or discolor within the first year following attack. However, if the summer of attack is unusually warm and dry, foliage color change can occur by early fall. Normally, however, during the second summer following spruce beetle attack, most needles will turn yellowish-red. Some needles even remain green until the third summer, or up to 2 years after the initial infestation (Schmid_and_Frye_1977). The difference in foliage fading is probably due to two factors: (1) Engraver beetles disperse and attack host material sooner than spruce beetles; and (2) Most engraver activity in standing trees occurs in interior Alaska where summer temperatures are warmer than those encountered in south-central Alaska thereby hastening the drying and fading of recently killed trees.
IDENTIFICATION OF LIFE STAGES - Adults
Adult engraver beetles are small (0.3-0.6 cm long), cylindrical, reddish-brown to black beetles (Figure: 4) (Holsten and Werner_1987). The head is not visible when the insect is viewed from above, unlike the spruce beetle whose head is quite visible. At first glance, engraver beetles may be confused with spruce beetles (Figure: 5). It is important to remember that the posterior margins of the wing covers on spruce beetles are evenly rounded, while Ips beetles have wing covers with concave margins and tooth like projections (Figure: 6). I. perturbatus is larger than the other commonly encountered Alaskan engraver species such as I. tridens and I. borealis. However, microscopic identification of the declivity and the number and shape of the spines may be needed to distinguish one species from another (Beckwith_1972).A distinguishing characteristic of I. perturbatus is that the third declivital spine is conical distally with an acute tip (e.g. similar to the "ace of spades") (Hopping_1963).
IDENTIFICATION OF LIFE STAGES - Eggs, Larvae and Pupae
The eggs of engraver beetles are oblong, pearly white, and < 1/16 inch (1.5 mm) long. The larvae are stout, cylindrical, legless grubs that pass through 4 larval stages (instars) and reach a length of 1/8 inch at maturity (Figure: 7). The pupae are opaque white, inactive, and somewhat similar in size and shape to adults (Figure: 8) (Wood_1982).
LIFE CYCLE - Duration
I. perturbatus normally completes its life cycle in 1 year in Alaska (Holsten_and_others_2001, Holsten and Werner_1987). Dispersing adults attack fresh host material soon after emergence in the spring. Egg galleries are initiated under the bark after mating, an average of 50 eggs are deposited, and larvae hatch with 7 to 10 days. The mean density of breeding galleries in white spruce in Alberta, Canada was 217 galleries/m2 of bark surface. (Robertson_2000) It is believed that I. perturbatus adults only establish one set of galleries in Alaska and do not re-emerge and re-attack the same or neighboring tree (Salisbury, Pers. Comm. 1998). Earlier biological studies undertaken in eastern Canada (Gobeil_1936) indicated that the adult stage lasted nearly two years. During the first complete summer as adults, the females lay two sets of eggs. The following spring they lay a third set and die during the second summer.
Larvae feed and develop on phloem tissue and develop into pupae. Feeding larvae may scour the xylem (wood) tissue, thus the common name of engravers. The pupal stage lasts approximately ten days; pupae then transform into new adults. New adults remain under the bark of the infested tree for a few weeks before emerging from the infested tree and dropping to the ground where they overwinter in the duff layer (Gobeil_1936, Watson_1927, Robertson_2000). Studies undertaken in interior Alaska (Salisbury, Pers. Comm. 1999) have shown that emerging new adults overwinter within 10' of the host substrate. Fewer adults overwinter in the duff on the north side of the brood tree or slash. This is in contrast to other species of Alaskan engravers (I. tridens, I. borealis) whose newly formed adults overwinter under the bark in the tree stem where they developed. The following spring, these over-wintered "new" adults emerge, disperse, and attack new, fresh host material.
LIFE CYCLE - Adult Dispersal
Newly formed adults do not disperse far to overwintering sites (Salisbury, Pers. Comm. 1998). They simply chew through the bark of the tree in which they developed and fall to the forest floor where they overwinter in the duff layer (Watson_1927, Robertson_2000). I. perturbatus adults emerge from the forest floor duff layer in the spring as soon as the snow has disappeared and the ground has thawed (Gobeil_1936, Holsten and Werner_1987). Time of spring emergence depends on temperature and normally occurs from mid-April on when ambient temperatures exceed 150C (Gara and Holsten_1975). Most I. perturbatus adults disperse up to 30 m from their overwintering sites but have been found to fly up to 120 m from a point of dispersal (Werner and Holsten_1997). Dispersal distance, however, is difficult to establish. In Europe, I. typographus adults can disperse more than 6 kilometers (Duelli et al._1997).
LIFE CYCLE - Gallery Development
Male Ips adults initiate the attacks on fresh host material. This is in contrast to spruce beetles where the female initiates the attack. After boring through the outer bark, male beetles construct a nuptial chamber in the inner bark (phloem) next to the sapwood (xylem). The male is joined by an average of five females, and mating takes place in the nuptial chamber. This is in contrast to the monogamous spruce beetle. Each Ips female then constructs her own egg gallery, which radiates out from the nuptial chamber, many times in a tuning-fork configuration (Figure: 9). Gobeil (1936) and Robertson (2000) has stated that females are capable of constructing multiple egg galleries. This, however, has not been documented in Alaska (Salisbury, Pers. Comm. 1998). Ips egg galleries are kept clear of boring dust by the parent adults. This characteristic distinguishes engraver galleries from those of spruce beetles whose galleries can be partially blocked with packed boring dust. (Figure: 10) illustrates the difference between larval galleries produced by spruce beetles and those produced by Ips beetles. Eggs are laid along the sides of the galleries and hatch into larvae which feed on the phloem tissue perpendicular to the egg gallery. The phloem tissue becomes severed by larval feeding, and the tree dies. Phloem tissue is necessary for the downward movement to the roots of nutrients produced during photosynthesis in the foliage.
Large diameter (>10" dbh) infested spruce can produce enormous quantities of new adults. It has been documented that 2,000 mated pairs of Ips adults produce as many as 22,000 young beetles from a 48' foot section of infested white spruce (Gobeil_1936).
INDIVIDUAL TREE SUSCEPTIBILITY
INFESTATIONS - Effect of Breeding Material
In spruce stands that have not been subjected to a major disturbance, endemic engraver beetle populations are normally maintained in recent (less than 1 year on the ground) windthrown trees, trees weakened by stresses such as root disease or fire, or broken tops and limbs. If such host material has been on the ground for more than six months, it is of little <risk> for future engraver beetle build-up.
With favorable weather conditions and favorable breeding material, endemic beetle populations may increase to sufficiently high levels to begin attacking "healthy" standing trees. Most outbreaks in standing trees originate in spruce stands that have experienced some form of major disturbance during, or followed by, a period of favorable weather conditions (Holsten and Werner_1987, Gobeil_1936).
Risk and Hazard models have not been developed for Alaska engravers as they have been for spruce beetle (Reynolds_and_Holsten_1994b, 1995). However, the definition and concept of both risk and hazard are useful and presented below:
Risk is a measure of the likelihood (probability) of an outbreak occurring (Reynolds_and_Holsten_1994b). The risk of an outbreak depends both on stand hazard and on the size of the available beetle population (Figure: 11). Other factors that are important for the determination of risk include beetle population size and weather conditions. These determinants of risk can vary considerably between years. Thus, risk analyses are most useful for short-term tactical planning.
Hazard is a measure of the degree of damage that can be expected in a spruce stand IF an engraver beetle outbreak OCCURS. That is, it is a measure of a stand's predisposition to attack, or susceptibility. Stand hazard is influenced by site characteristics as well as stand characteristics, both of which in turn effect tree vigor. Because stand characteristics change relatively slowly over time, stand hazard also changes slowly over time. Thus, analyses of hazard are useful for long-term, strategic pest management. (Reynolds_and_Holsten_1995)
Note that a spruce stand can be classified as very high hazard, but be at only low to moderate risk due to a small beetle population size in or near the stand of interest.
Fire, wind storms, river flooding, snow breakage are natural disturbances that produce large volumes of dead or damaged spruce, any of which is ideal breeding material for engraver beetles. Human activities including road building, construction of right-of-ways, and logging can similarly provide engravers with large amounts of breeding material such as cull logs, tops and branches.
Infested logging residuals will not contribute significantly to buildup of engraver beetle populations if:
An increase in engraver beetle populations to outbreak levels generally depends both on the availability of large volumes of suitable breeding material (typically provided by a major disturbance) and on favorable weather.
Most spruce trees in south-central and interior Alaska can experience prolonged periods of water stress in late spring/early summer. The duration of this water stress is dependent on ambient temperatures. If it is unseasonably warm and dry, spruce will transpire large amounts of water. However, soil moisture is usually unavailable to "re-charge" the tree at this time as many soils are frozen. Due to this "lack" of water and increased transpiration, spruce become water stressed. Increased water stress results in increased tree susceptibility to engraver beetle attack as the production and movement of resin to the site of beetle attack is dependent on the tree's water balance.
For example, 1986 aerial insect and disease surveys noted more than 16,000 acres of engraver infestations in the Fairbanks area (Holsten_1986). This outbreak was believed to have developed from a combination of factors: (1) Large amounts of breeding material (fire scorched spruce) from the Rosy Creek fire and thousands of acres of scattered broken spruce tops originating from heavy snow falls during the 1984-85 winter. Ips populations rapidly built-up in this widely available host material during the spring/summer of 1985. This was followed by (2) an abnormally low snow fall in 1985-86 and drought-like conditions in the spring of 1986, resulting in thousands of acres of water stressed standing spruce. A huge Ips dispersal flight "took advantage" of these spruce producing the resulting spruce mortality on 16,000 acres.
INFESTATIONS- Individual Tree Susceptibility
As an outbreak begins to build, engraver beetles begin to attack the larger-diameter spruce trees first. Likewise, individual trees that are fire scorched or infected by root pathogens, severely water stressed, or mechanically damaged are more susceptible to attack. Results from a study in the Noatak River drainage of interior Alaska showed that 8 percent of white spruce stems sampled were being eliminated by a combination of windthrow, porcupine damage, and resultant Ips activity (Gara and Holsten_1975). Most spruce having 60 percent or less of their circumference girdled by porcupines were able to successful repel attacking Ips populations. When 60 percent of more of the tree's circumference was girdled, the probability of a successful Ips attack was increased. Apparently the dispersing Ips were attracted to volatiles emanating from the injured spruce and the insects then proceeded to attack these hosts indiscriminately.
If an infestation persists in a stand, smaller diameter trees will eventually be attacked. A recent I. perturbatus outbreak in the Granite Creek area of the Kenai Peninsula illustrates this point (Holsten_1996, 1997). Ips-killed Lutz spruce had an average dbh of 4.5" vs. 2.8" for uninfested spruce in 1996, the first year of the outbreak. This trend continued in 1997. When an outbreak is intense, spruce as small as 1-2" in diameter may be attacked and killed. The presence of non-infested standing spruce trees next to infested trees indicates the individual tree variation in susceptibility to engraver beetle attack.
ENGRAVER POPULATIONS - Effect of Site Conditions
On a broad geographic scale, marked differences occur in the frequency and persistence of engraver beetle outbreaks. To a large extent, these differences are explainable in terms of regional climatic effects on engraver populations.
Outbreaks are uncommon in maritime Sitka spruce stands. The cool, wet coastal climate of the maritime environment tends to keep beetle populations at relatively low levels in part because spring weather is rarely favorable for the short, concentrated dispersal periods that favor occurrence of outbreaks.
Engraver outbreaks are more common in south-central Alaska than southeast, but less so than in interior Alaska. South-central Alaska's climate is transitional between maritime and continental. However, engraver activity has increased in the last few years (Holsten_1996, 1997, 1998) and is believed to be in part due to the increased level of spruce beetle activity which has provided abundant breeding material for engraver beetles. Most spruce beetle attacked trees are also colonized by engravers, especially in the tops of the trees. Also, climate has changed throughout Alaska; it has significantly warmed on the Kenai Peninsula and elsewhere for the last 80 years (Berg_Pers. Communication 1998). This warming trend probably has increased over-wintering survival of Ips as well as increasing favorable spring dispersal conditions.
In contrast to the maritime and south-central regions of Alaska, severe engraver beetle outbreaks have occurred fairly regularly in the continental climatic zone of interior Alaska. Summer weather in interior Alaska is much warmer and dryer than that in south-central. Such conditions favor Ips development over that of spruce beetles. In many cases, Ips beetles out-compete spruce beetles for the limited breeding material in interior Alaska.
ENGRAVER POPULATIONS - Effect of Stand Conditions
Any stand condition that reduces tree vigor also increases the <hazard> associated with an engraver beetle outbreak. For example, older spruce stands tend to be less vigorous than younger stands, and thus more susceptible if an engraver beetle outbreak occurs. That is, they are physiologically less able to defend themselves against beetle attacks than thriftier, younger stands.
Higher stand density and basal area may also increase hazard through more direct effects on tree vigor as a result of increased inter-tree competition for nutrients, water, and sunlight.
Finally, other factors being equal, hazard increases with increasing proportion of spruce basal area in the stand. That is, there is more available "food" for engraver beetle population buildup.
MANAGEMENT STRATEGIES - Management Goals & Objectives
Forest managers can develop various strategies to avoid or reduce resource losses from engraver beetles. Before developing a strategy, the forest manager must evaluate the resource values, economics, and accessibility of each stand. The beetle population level must also be considered for shorter term tactical planning. Being knowledgeable of engraver population levels can help determine whether a preventive or suppression strategy will be invoked. This is especially important when dealing with Ips beetles as populations can increase to epidemic levels in a very short period of time!
The primary preventive strategy should be silvicultural treatments of potentially susceptible stands to maintain a healthy stand with a moderate growth rate. Properly applied silvicultural practices can maintain the forest diversity needed to provide the range of products and amenities available from the forest. Silvicultural treatments have greater long-term effectiveness, because these treatments modify stand characteristics.
If beetle populations are threatening, then strategies involving suppression methods are more appropriate. Suppression measures including silvicultural, physical, and chemical measures are available to forest managers (Werner_1988). Some methods are suitable only for beetle populations in down host material such as logging slash and broken tops; other methods are better suited for infestations in standing trees. Most suppression methods are short-term tactical responses to existing beetle populations and, therefore, correct only the immediate situation.
MANAGEMENT STRATEGIES - Silvicultural Methods
Sanitation overstory removal involves the removal of all infested and susceptible spruce to encourage regeneration of a new vigorous stand.
Sanitation partial cut involves the removal of infested and susceptible (low vigor) spruce trees 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, however, may be more susceptible to windthrow.
Trap trees are large-diameter green trees that are felled before beetle flight. Trap trees should not be bucked or delimbed. Trap trees can absorb many times the number of engraver beetles that a standing tree will absorb. Once infested, trap trees should be removed from the forest (Werner_1988). If they are not removed in a timely fashion, large numbers of new adults may emerge and attack nearby uninfested standing spruce.
Likewise, there is some indication from studies conducted in ponderosa pine stands in southern Idaho (Knopf_1982) that the attraction and containment of Ips beetles by large slash piles is feasible. Ponderosa pine stands were thinned using a Hahn Harvester. Little or no slash was left scattered on the ground. This operation concentrated lopped tops, limbs, cull pieces up to 6" in diameter at a centralized location. These slash piles were large; approximately 90' long, 30' wide, and 20' high and were readily attacked by Ips spp. Emerging new adults would re-attack the slash piles, working their way deeper into the pile. Number of individuals produced from succeeding generations, however, became lower and lower as the suitability of the slash was decreased over time. No new attacks were observed in the surrounding thinned stand.
Guidelines for Reducing Engraver Beetle Attacks (Holsten & Werner_1987):
Damaged and windthrown trees should be removed from spruce stands or homeowners' properties. Trees should be used or destroyed by burning, chipping, or burying.
Partially burned trees in the fringe area of a wildfire should be harvested immediately after the fire, if the fire occurs in the early spring. Otherwise, you can harvest before the next beetle flight.
Timber harvest should be scheduled after the beetle flight period but not within 3 months of the next flight period.
Slash from logging and thinning operations should be destroyed if possible. If this is not possible, cutting slash into short pieces and scattered, not piling, will reduce its suitability as breeding sites.
Mechanical damage to standing trees should be avoided, and excess soil should not be placed on top or removed from the area over the root zone.
Infested firewood should not be stacked or stored in areas surrounded by live trees.
Ips beetle management strategies have included both harvesting freshly attacked trees and the use of felled live trees to serve as traps (Werner_1988). Trap trees may be of two types: conventional and lethal. The objective of both is to absorb dispersing adults into pre-selected felled trees in order to protect adjacent standing timber (Figure: 12, Figure: 13). Conventional trap trees are large diameter, live white or Lutz spruce which are felled to attract Ips beetles during their dispersal flight period from mid-May to early June. The beetle brood in these trap trees must be killed by utilizing the tree for lumber, by debarking, chipping, burning, burying, or chemical treatment to the bark. This must be done before the new adults emerge in mid-July. Lethal trap trees have not been commonly used in Alaska. Lethal traps are created by introducing a silvicide, such as monosodium methanearsonate (MSMA), an organic arsenical, applied in an axe frill around the circumference of a live standing tree. In interior Alaska, lethal trap trees should be treated the first week of May and felled two weeks later. Conventional trap trees can be felled in late April (Werner_1988).
Trap trees could be used within the boundary of timber sales in spruce stands prior to logging in order to reduce the beetle population. Trap trees should be felled in a direction which provides the most shade; they should not be bucked or delimbed.
The use of pheromones, specifically the attractant blend of Ipsdienol + cis-verbenol + Ipsenol, will greatly enhance the effectiveness of both conventional and lethal trap trees (Holsten_and_others_2000).
MANAGEMENT STRATEGIES - Physical Methods
Solar heat involves exposing infested logging residuals or windthrow to direct sunlight to kill inhabiting larvae. To maximize brood mortality, slash 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. Although effective in the lower-48, especially in the southwest, it is believed that summer temperatures in interior Alaska are not high enough to kill developing larvae.
The use of polyethylene sheeting to control Ips beetle by covering infested logging slash in Arizona has been investigated (Buffam & Lucht_1968). An average mortality of 89 percent of engraver larvae was obtained with clear polyethylene, the use of which provided significantly higher inner bark temperatures than occurred with uncovered slash (57oC vs. 39oC, respectively). The use of clear polyethylene for the control of bark beetles in wood residue and firewood is a recommended technique in California (Sanborn 1991). In south-central Alaska, covering stacks of spruce firewood with either clear or black polyethylene sheeting did not raise log temperatures high enough to kill spruce beetle brood in the logs (Holsten & Werner_1993). Similar studies conducted in interior Alaska for the control of I. perturbatus showed that 42% fewer Ips adults emerged from piles of infested spruce compared to uncovered infested spruce piles. The greatest differences in emergence were noted from the top layer of infested spruce (Salisbury Pers. Comm. 1999). It is uncertain, however, if this same level of mortality can be achieved by covering large infested logging decks and slash piles with clear polyethylene sheeting.
Fire - Use of fire involves piling and burning infested logging slash and windthrow to destroy brood that inhabits the material. The infested material is usually green and difficult to burn, but the bark only has to be scorched to destroy brood inhabiting the material. Care must be taken not to scorch live standing residual spruce. Such scorched trees can become attractive to dispersing engraver beetles.
Fire could also be used as a post-harvest treatment, especially in clear-cuts. As previously discussed, new adults emerge from host material and overwinter nearby in the duff layer (Salisbury, Pers. Comm. 1999). The use of prescribed fire in the late summer and early fall in interior Alaska for fuel treatment and habitat improvement is becoming more common. Such burns also provide the benefit of destroying over-wintering adults.
MANAGEMENT STRATEGIES - Chemical Methods
Pheromones are chemical substances that influence insect behavior. Synthetic pheromones, such as aggregating and anti-aggregating pheromones, increase the attractiveness of trap trees, attract beetles into trees to be cut, or discourage infestation of high-value trees. However, many of these synthetic pheromones have not received registration from the Environmental Protection Agency and, as such, are only used in research or limited management activities. Pheromones used in traps, however, require no registration and can be used in certain management strategies such as trap out.
Insecticides, such as Carbaryl, can be applied to the boles of uninfested spruce to kill attacking beetles. Carbaryl applied as a 1-2 percent solution has provided 100 percent protection from attacking spruce and engraver beetles for at least 2 years; almost 85% protection is achieved through the third year (Werner_and_others_1986).
Pheromones are chemical messengers produced by an individual of a species that affects the behavior of another individual of the same species. Engraver beetles produce both attractant (both males and females respond) and anti-aggregation (both sexes are "repelled") pheromones (Werner_1993).
The attractant pheromone (a combination of Ipsdienol + cis-verbenol + Ipsenol) (Moeck et al. _1985, Holsten_and_others_2000) attracts dispersing engraver beetle adults during the period of beetle flight, promoting a local beetle population buildup on individual trees or groups of trees. "Pioneer" beetles first attack a susceptible spruce, then produce an attractant pheromone which signals other nearby dispersing beetles to attack the tree. This mass attack is necessary to overcome the tree's primary defense strategy.
The anti-aggregating pheromone (Verberone) is produced by engraver beetles when the optimum beetle population size in a tree is reached or exceeded. This prevents buildup of excessive numbers of beetles within a tree or very localized area. This regulation of beetle population size helps reduce competition for limited food and habitat among developing engraver beetle larvae.(Holsten_and_others_2001
The chemical composition of both types of pheromone has been determined, allowing the production of synthetic pheromones that can be used as forest management tools.
Attractant pheromones significantly increase the attractiveness of conventional and lethal trap trees. Attractant-baited funnel traps can be used in pre- and post-logging situations either as grid trapping for overall suppression of beetles in susceptible areas designated for select harvest or thinning, or as barrier trapping to prevent the movement of beetles from sources of high beetle density or brood material to adjacent uninfested stands (Werner_1988, Holsten_1997, Holsten_1998) (Figure: 14).
Chemical treatment of host material is another option in the management of engraver populations (Werner_1988) (Werner & Holsten_1992). There are two chemical approaches: (1) Remedial control in which infested material is treated to kill beetles under the bark and when they emerge from their breeding sites, and (2) Preventive control in which uninfested host material is treated to prevent attacks from beetles. Standing trees should be sprayed to drip point to a height of 40 feet. The entire surface of felled trap trees and log decks that can be sprayed should be treated to the drip point. Preventive treatments should be applied from late-fall to late-April before the emergence and flight period of dispersing engraver adults. Remedial treatments can be applied from late June to early July prior to the emergence of the new generation. The use of protection clothing is required and pesticide label directions are the Law and must be followed. For further information on pesticide use, contact your local Alaska Cooperative Extension Office or the Department of Environmental Conservation (907- 745-3236).
Recently, there has been limited use of bole implantation of systemic insecticides as preventive and remedial techniques against bark beetles in south-central Alaska. Despite the frequent claims that insecticide injection is effective in protecting trees from bark beetle attack, studies undertaken in Alaska have shown the use of bole implantation of systemic insecticides to be ineffective in preventing bark beetle attack (Shea_Holsten_Hard_1991). The use of this strategy, however, is effective in protecting high-value forest and shade trees from a variety of chewing and sucking insects such as caterpillars and aphids.
Beckwith, R.C. 1972. Key to adult bark beetles commonly associated with white spruce stands in interior Alaska. USDA For. PNW Res. Note PNW-189. 6 pp.
Abstract: A dichotomous key enables the determination of adult Scolytidae commonly found in white spruce stands in interior Alaska including the Kenai Peninsula. Schematic drawings are included.
Beckwith, R.C., J.O. Wolff, and J. C. Zasada. 1977. Bark beetle response to clear-cut and shelterwood systems in interior Alaska after whole tree logging. USDA For. Serv. PNW Res. Note PNW-287. 7 pp.
Abstract: After logging, adult populations of scolytids declined in clearcuts; adults increased dramatically the 1st year and declined the 2nd year in the shelterwoods. The spruce beetle does not appear to be a major threat after whole tree logging under conditions of the study.
Beckwith, R.C. 1972. Scolytid flight in white spruce stands in Alaska. Can. Ent. 104: 1977-1983.
Abstract: Within white spruce stands, Dendroctonus rufipennis, Ips spp., and Typodendron lineatum disperse in late May and early June; other scolytids fly during June and July. Flight in interior Alaska precedes by about 2 weeks that on the Kenai Peninsula.
Bright, D.E. 1976. The insects and arachnids of Canada, Part 2. Canadian Dept. of Agriculture Publ. 1576. 241 pp.
Abstract: A good reference for the majority of scolytids affecting Alaskan spruce forests with general descriptions of hosts and biology.
Buffam, P.E. and D.D. Lucht. 1968. Use of polyethylene sheeting for control of Ips spp. in logging debris. Jour. of Econ. Entomol. 61: 1465-1466.
Abstract: Use of clear polyethylene sheeting significantly increased the mortality of developing Ips beetles vs. untreated controls in a the hot, dry climate of southwestern U.S.
Connell, J.H. 1978. Diversity in tropical rain forests and coral reefs. Science 199: 1302-1310.
Abstract: Not available.
Copes, D.L. and R.C. Beckwith. 1977. Isoenzyme identification of Picea glauca, P. sitchensis, and P. lutzii populations. Bot. Gaz. 138(4): 512-521.
Abstract: Electrophoretic techniques were used to identify stands of pure Sitka spruce and pure white spruce and spruce stands in which introgressive hybridization between the white and Sitka spruce had occurred. Much of the west side of the Kenai Peninsula appeared to be a hybrid swarm area, with stands containing both Sitka and white spruce genes.
Daniel, T.C., Orland, B., Hetherington, J. and J.L. Paschke. 1991. Public perception and attitudes regarding spruce bark beetle damage to forest resources on the Chugach National Forest, Alaska. Final Report prepared for USDA Forest Service, Forest Pest Management, R10. 35 p.
Abstract: Describes the public perception of spruce beetle impact on the scenic quality of the landscape. Spruce bark beetle impacts significantly reduce the scenic quality. Publics are in favor of prevention, mitigation, and restoration of impacted resources.
Daubenmire,R. 1968. Some geographic variations in Picea sitchensis and their ecologic interpretations. Can. J. Bot. 46: 787-798.
Abstract: Not available.
Duelli, P., Zahradnik, P., Knizek, M. and B. Kalinova. 1997. Migration in spruce bark beetles (Ips typographus L.) and the efficiency of pheromone traps. J. Appl. Ent. 121: 297-303.
Abstract: Ips dispersed at least 4 kilometers through non-host type. The use of trap-out utilizing pheromones may reduce local Ips populations but will not prevent immigration of beetles into the stand in question. Likewise, more than 50% of marked Ips adults were not responsive to pheromone baited traps and dispersed out of the study stand.
Flemming, R.A. and J.N. Candau. 1998. Influences of climatic change on some ecological processes of an insect outbreak system in Canada's boreal forests and the implications for biodiversity. Environ. Monit. and Assess 49: 235-249.
Abstract: Insect outbreaks are a major disturbance factor in Canadian forests. In addition, the likelihood of wildfire often increases after insect attack, so the unpredictability of future insect disturbance patterns adds to the general uncertainty of fire regimes. It is argued that a species-level, preservationist approach may have unwanted side-effects, be cost-ineffective, and ecologically unsustainable.
Furniss, R.L. and V.M. Carolin. 1977. Western Forest Insects. USDA For. Service Miscell. Publication No. 1339. 654 pp.
Abstract: Extensive survey of the most damaging and more common insects pests of western forests, both conifer and hardwood.
Gara, R.I., R.A. Werner, M.C. Whitmore, and E.H. Holsten. 1995.Arthropod associates of the spruce beetle Dendroctonus rufipennis (Kirby) (Col., Scolytidae) in spruce stands of south-central and interior Alaska. J. Appl. Ent. 119: 585-590.
Abstract: The impact of competitors, including Ips, and predators on spruce beetle broods was studied at endemic and epidemic levels. Competing Dryocoetes affaber broods were the most important interspecific mortality of larval spruce beetle broods. The impact of dipteran and coleopteran predators and hymenopterous parasites on spruce beetle survival was of less importance than this interspecific competition.
Gara, R.I. and E.H. Holsten. 1975. Preliminary studies on arctic bark beetles (Coleoptera: Scolytidae) of the Noatak River drainage. Z. Ang. Ent. 78: 248-254.
Abstract: Ips borealis host selection behavior was opportunistic as insects readily attacked injured spruce even if the attacks were unsuccessful. Most scolytid species studied flew whenever temperatures were above 15oC. Ips attack occurred primarily on the warmest quadrant of their host trees.
Gobeil, A.R. 1936. The biology of Ips perturbatus. Canadian Journal of Research. Vol. 14, Sec. D., No. 12: 181-204.
Abstract: This species generally breeds on trees killed by Dendroctonus picaperda (= rufipennis). There is one generation per year. Emergence from the duff layer occurs in early spring. During their first complete summer as adults, females lay two sets of eggs. The following spring they lay a third set of eggs and die. Ips perturbatus can produce 2448 egg tunnels, 22,512 young beetles, 58,800 egg niches in 48 feet of bole surface and a mortality rate of 58%.
Holsten, E.H. 1996. Ips tridens; A pest of managed stands? USDA For. Serv. Alaska Region FHP Biol. Evaluation R10-TP-64. 8pp.
Abstract: An unusual flare-up of Ips tridens occurred in south-central Alaska as a result of population build-up in the tops of spruce beetle infested trees and the subsequent infestation of standing green residual spruce. Factors concerning this population build-up are discussed.
Holsten, E.H. 1997. Ips tridens; A pest of managed stands? 1997 Update. USDA For. Serv. Alaska Region FHP Biol. Evaluation R10-TP-71. 7pp.
Abstract: The determination of Ips tridens was later changed to I. perturbatus in the Granite Creek area. The engraver infestation has killed approximately 40% of the standing live spruce in 2 years. Large diameter spruce were preferentially attacked. The use of pheromones as a control tactic is discussed.
Holsten, E.H. 1998. Ips perturbatus; A pest of managed stands? 1998 Update. USDA For. Serv. Alaska Region FHP Biol. Evaluation R10-TP-71. 7pp.
Abstract: The I. perturbatus outbreak in the Granite Creek area subsided after 3 years. Approximately 50% of the residual spruce was killed in a 3-year period. The use of baited funnel traps as a control technique is discussed.
Holsten, Edward H. and R.A. Werner. 1993. Effectiveness of polyethylene sheeting in controlling spruce beetles (Coleoptera: Scolytidae) in infested stacks of spruce firewood in Alaska. Res. Pap. PNW-RP-466. Portland, OR: USDA For. Serv., PNW Res. Station. 6pp.
Abstract: Covering stacks of spruce firewood with either clear or black polyethylene sheeting does not raise log temperatures high enough to kill spruce beetles in the logs. Based on the results of this study, authors do not recommend the use of polyethylene sheeting as a remedial measure for the reduction of spruce beetle brood in infested firewood or log decks in south-central Alaska.
Holsten, E.H.; Werner, R.A.; DeVelice, R.L. 1995. Effects of a spruce beetle outbreak and fire on Lutz spruce in Alaska. Environ. Entomol. 88(6):1539-1547.
Abstract: Summarizes the results of 20 years of monitoring 30 permanent plots in an area heavily impacted by the spruce beetle. Results demonstrated an overall decline in the number of plant species as a result of canopy opening. The invasion and spread of Calamagrostis and Epilobium caused most of the plant reductions due to the effects of competition.
Holsten, E.H. 1986. Evaluation of Ips perturbatus caused white spruce mortality in the Fairbanks, AK area. USDA For. Service Informal Report. 8pp.
Abstract: Ips caused white spruce mortality (23%) occurred in mature spruce stands averaging 171 sq. ft./ac. Mortality declined after 3 years. Engraver populations increased rapidly as a result of large quantities of host material (broken tops) from a heavy snow storm. Mortality of standing spruce was a result of large dispersing Ips populations as well as drought-like spring conditions which water-stressed standing spruce.
Holsten, E.H. and R.A. Werner. 1987. Engraver beetles in Alaska forests. USDA For. Serv. Leaflet. 6pp.
Abstract: Descriptive brochure describing life cycle, population dynamics, and management strategies of Alaska engraver beetles with emphasis on interior Alaska.
Hopping, G.R. 1963. The natural groups of species in the genus Ips De Geer (Coleoptera: Scolytidae) in North America. Can. Entomol. 95: 508-516.
Abstract: There are now 32 species of Ips recognized in North America, with a few more as yet undescribed. This paper defines the groups of closely related species with observations on the group relationships of species from other parts of the world.
Keen, F.P. 1952. Insect enemies of western forests. USDA Misc. Publ. No. 273. 280 pp.
Abstract: Extensive survey of the most damaging and more common insects pests of western forests, both conifer and hardwood.
Knopf, J.A.E. 1982. Attraction and containment of Ips beetles by large slash piles. USDA For. Serv. Intermountain Region Forest Pest Management Internal Report 3430, 82-8. Boise, Id. 4 pp.
Abstract: This report evaluates the attraction and containment of Ips beetles in over-size slash piles created when ponderosa pine stands were logged. Engraver beetle attacks in residual stands were minimized and/or virtually eliminated when two generations of beetles remained in the large slash piles.
Little, E.L. 1953. A natural hybrid in Alaska. J. Forest. 51: 745-747.
Abstract: Not available.
Lowell, E.C. and S.A. Willits. 1998. Lumber recovery from beetle-killed spruce trees, Kenai Peninsula, Alaska. West. Journ. of Applied Forestry, Vol. 13(2): 54-59.
Abstract: Defect present prior to attack by beetles played a significant role in recovery results. recommendation is to have two deterioration classes: one for live and infested trees and a second for dead trees. Volume and value recovery differed significantly between these two classes. Without any beetle activity at all, 24% of the logs in this study had existing rot and 18% some other defect, none of which had any relation to deterioration class. Sap rot and weather check, coming in after beetle attack, not only decrease volume recovery, but more importantly, decrease lumber grade recovery from the outer portion of the tree thereby lowering value recovery as well.
Moeck, H.A.; L. Safranyik; C.S. Simmons; and C.M. Lawko. 1985. Ips tridens (Coleoptera: Scolytidae) attracted by Ipsdienol plus cis-verbenol. Can. Ent. 117: 955-960.
Abstract: Funnel traps baited with Ipsdienol plus cis-verbenol caught significantly more adults than any other lure combination. Cis-verbenol, when used alone, caught no more adults than unbaited funnel traps.
Reynolds, K.M. and E.H. Holsten. 1994. Classification of spruce beetle hazard, Dendroctonus rufipennis (Kirby), in Lutz spruce, Picea lutzii Little, stands on the Kenai Peninsula, Alaska. Can. J. For. Res. 24:1015-1021.
Abstract: Presents a statistically valid hazard (defined as the amount of spruce basal area that can be lost to spruce beetles in 5-10 yrs) model. Data collected over the past ten years from the Kenai Peninsula.
Reynolds, K.M. and E.H. Holsten. 1994. Estimating priorities of risk factors for spruce beetle outbreaks. Can. J. For. Res. 24:3067-3074.
Abstract: Through the use of an analytical hierarchy approach, describes the most important factors responsible for risk; risk defined as the probability of an outbreak within the next 2-3 yrs.
Reynolds, K.M. and E.H. Holsten. 1997. SBexpert Users Guide (Version 2.0): A Knowledge-based-decision-support system for spruce beetle management. USDA For. Serv., PNW-GTR-401. 61 pp.
Abstract: Users guide for the management of spruce bark beetle problems. Includes electronic text book and literature search.
Reynolds, K.M. and E.H. Holsten. 1995. Classification of spruce beetle hazard in Lutz spruce and Sitka spruce stands on the Kenai Peninsula, Alaska. Forest Ecology and Management 84 (1996): 251-262.
Abstract: Discusses models used to determine significant variables of hazard to spruce stands if attacked by spruce beetles. Important variables include: Total basal area of a stand, percent of the basal area that is comprised of spruce, and the percent of the spruce that is over 12" in dbh.
Sanborn, S.R. 1991. Controlling bark beetles in wood residue and firewood. Tree Notes 3. [Location of publisher unknown]: California Dept. of Forestry and Fire Protection.
Abstract: Use of clear polyethylene sheeting is recommended as a remedial control of Ips infested firewood in California.
Schmid, J.M.; Frye, R.H. 1977. Spruce beetle in the Rockies. U.S. For. Serv. Gen. Tech. Rep. RM-49, Rocky Mt. For. and Range Exp. Stn., Fort Collins, Colo. 38 p.
Abstract: A summary of literature to 1977 detailing life cycle, taxonomy, behavior, history of outbreaks, detection, evaluation, and management.
Schulz, B. 1995. Changes over time in fuel-loading associated with spruce beetle-impacted stands of the Kenai Peninsula, Alaska. USDA For. Serv., Forest Health Mgt. Tech. Rpt. R10-TP-53. 17 p.
Abstract: 5-10 years after a spruce beetle outbreak, large woody debris amounts increased from the normal 2 tons/acre to more than 30 tons/acre. Likewise, Calamagrostis grass, fine flashy fuel, increased significantly.
Scott, G.M.; Bormett, D.W.; Sutherland, N.R.; Abubakr, S.; Lowell, E. 1996. Pulpability of beetle-killed spruce. USDA Forest Service, Forest Products Laboratory Research Paper FPL-RP-557. 7 p.
Abstract: Results showed that live and dead spruce beetle killed trees can be pulped effectively. The presence of sap rot decay was found to be an important indicator of pulping efficiency and resultant pulping quality. Log deterioration had mixed effects on paper properties.
Shea, P.J.; Holsten, E.H.; and J. Hard. 1991. Bole implantation of systemic insecticides does not protect trees from spruce beetle attack. Western Journ. of Applied Forestry 6(1):4-6.
Abstract: A bole implantation of the systemic insecticide acephate (Orthene) did not protect unattacked spruce trees from spruce beetle attack nor did the use of systemic insecticides kill developing beetle brood when used as a remedial treatment. A discussion of the movement of systemic insecticides in plant tissue is included.
Stone, W.E. and M.L. Wolfe. 1996. Response of understory vegetation to variable tree mortality following a mountain pine beetle epidemic in lodgepole pine stands in northern Utah. Vegetatio 122: 1-12.
Abstract: The response of understory plant species diversity to increasing disturbance severity is consistent with the pattern predicted by the intermediate disturbance hypothesis. However, other explanations of this pattern are discussed. Although understory plant community richness was higher in beetle-killed stands than in unaffected stands, new species were not abundant and therefore did not contribute substantially to greater evenness in understory plant diversity.
Watson, E.B. 1927. Notes on the hibernation of the spruce bark beetle, Ips perturbatus in northern Ontario. The Canadian Entomol. Vol. 59:120-121.
Abstract: Ips perturbatus was found to overwinter in the duff layer near the host tree in which they developed.
Werner, R.A. 1988. Recommendations for suppression of an Ips perturbatus outbreak in interior Alaska using integrated control. In: Payne, T.L.; Saarenmma, H., eds. Integrated control of scolytid bark beetles; 1988 July 4; Vancouver, BC. IUFRO Working Party and XVII International Cong. Of Entomology Sym.
Abstract: Populations of I. perturbatus were reduced in stands of white spruce in interior Alaska using several integrated pest management strategies such as conventional and lethal trap trees, baited funnel traps, and preventive and remedial chemical treatments.
Werner, R.A. and E.H. Holsten. 1992. Effectiveness of Sevin with and without diesel for remedial control of spruce beetles (Coleoptera: Scolytidae) in infested spruce in Alaska. J. Econ. Entomol. 85(2): 473-476.
Abstract: Sevin SL was more effective in providing remedial control of emerging adults compared with nonemerged adults; Sevin 80S in diesel and Sevin SL provided adequate remedial control of 2nd-yr emerged adults. Sevin 80S in diesel provided the best remedial control of larvae but all other chemicals tested were ineffective for control of pupae. Remedial treatment of individual spruce trees infested with spruce beetles can probably significantly reduce the number of beetles that would normally emerge and attack adjacent standing green trees.
Werner, R.A. 1993. Response of the engraver beetle, Ips perturbatus, to semiochemicals in white spruce stands in interior Alaska. USDA For. Serv. PNW Research Station Res. Paper PNW-RP-465. 9 pp.
Abstract: Several pheromones, including Ipsdienol, attracted high numbers of I. perturbatus and species of the predator Thanasimus to baited funnel traps. Test results also indicated that attacks by I. perturbatus may be deterred by certain semiochemicals.
Werner, R.A. and E.H. Holsten. 1997. Dispersal of the spruce beetle, Dendroctonus rufipennis, and the Engraver Beetle, Ips perturbatus, in Alaska. USDA For. Serv. PNW Res. Station Res. Paper PNW-RP-501. 8 pp.
Abstract: Mark-release-recapture experiments demonstrated that most engraver beetles dispersed up to 30 m from their overwintering sites compared to most spruce beetles, which dispersed from 90 to 300 m. Engraver beetles were caught up to 90 m and spruce beetles up to 600 m from the point of release.
<<b>Werner, R.A. 1994. Forest insect research in boreal forests of Alaska. Entomol. (Trends in Agric. Sci.) 2: 35-46.
Abstract: A general overview of forest health concerns in Alaskan boreal forests with some discussion of current entomological research.
Werner, R.A. and E.H. Holsten. 1984. Scolytidae associated with felled white spruce in Alaska. Can. Ent. 116: 465-471.
Abstract: Pheromone baited traps and trap trees attracted an aggregate of 29 scolytid species associated with white spruce. The most abundant scolytids were Ips perturbatus, Ips tridens tridens, Polygraphus rufipennis, Dryocoetes affaber, Trypodendron lineatum and Scolytus piceae.
Werner, R.A. 1996. Forest health in boreal ecosystems of Alaska. The Forestry Chronicle Vol 72 (1): 43-46.
Abstract: A general view of forest health in Alaska with a discussion concerning resources affected and long-term productivity.
Wood, S.L. 1982. The bark and ambrosia beetles of North and Central America (Coleoptera: Scolytidae), a taxonomic monograph. Great Basin Naturalist Memoirs, Brigham Young University No. 6. 1359 pp.
Abstract: An exhaustive work pertaining to the taxonomy, and general biology of North and Central American scolytids.
Werner, R.A.; Elert, E.E.; Holsten, E.H. 1983. Evaluation of beetle-killed white spruce for pulp and paper. Can. J. For. Res. 13:246-250.
Abstract: There was no difference in pulp yield between trees dead for 1 year, and those dead as long as 50 years. Trees that had been dead for 50 years produced high quality pulp.
Werner, R.A.; Hastings, F.L.; Holsten, E.H.; Jones, A.S. 1986. Carbaryl and lindane protect white spruce Picea glauca from attack by spruce beetles Dendroctonus rufipennis (Coleoptera: Scolytidae) for three growing seasons. J. Econ. Entomol. 79:1121-1124.
Abstract: One and two percent carbaryl and 0.5% lindane were 100% effective after 16 months. After 3 years, 1% carbaryl was 89% effective, 2% carbaryl was 96% effective, and 0.5% lindane was 94% effective.
Downing, G.L. 1957. An Ips interpunctus infestation in white spruce of northern interior Alaska. USDA Forest Service, Forest Insect survey Reports of the Alaska Forest Research Center, Juneau, AK. Rpt. No. 2. 4p.
Abstract: The engraver outbreak lasted approximately 3-5 years and covered a gross timbered acreage of 1,152,000 acres or 1800 square miles. Approximately 40.3 cubic ft. vol./acre were killed during this outbreak.
Robertson, I.C. 2000. Reproduction and developmental phenology of Ips perturbatus (Coleoptera: Scolytidae) inhabitingwhite spruce (Pinaceae). The Canadian Entomologist 132: 529-537.
Abstract: Mean density of breeding galleries on the study trees was 217/m2. Individual females laid 48.9 eggs in galleries that reached 10 cm in length. Mortality from egg to adult was high (98%) during this 1-year study, likely a result of the intense crowding of galleries. Adult offspring emerged into the duff from mid-August into September indicating a 1-year life cycle.
Holsten, E.H.; Burnside, R.E.; Seybold, S.J. 2000. Attractant semiochemicals of the engraver beetle, Ips perturbatus, in south-central and interior Alaska. USDA Forest Service, Pacific Northwest Research Station Research Paper PNW-RP-529. 9 p.
Abstract: Field studies showed that a blend of racemic ipsdienol, 83&-(-)-cis verbenol, and >97%-(-)-ipsenol provided a strong attractant to baited funnel traps.
Lance, E.W. and Howell, S. 2000. Survey of songbirds during a spruce beetle (Dendroctonus rufipennis) outbreak on the Kenai Peninsula, Alaska. Northwestern Naturalist 81: 1-10.
Abstract: The greatest number of nesting birds was found in a post harvest area; the least number of birds were reported from a heavy spruce beetle infested area; with a significant reduction in Townsend Warblers and Ruby-crowned Kinglets.
Holsten, E.; Hennon, P.; Trummer, L.; Schultz, M. 2001. Insects and diseases of Alaskan forests. U.S. Department of Agriculture, Forest Service, Alaska Region, R10-TP-87. 242 p.
Abstract: This illustrated handbook describes the biology and damage of the more commonly encountered forest insects and disease of Alaskan forests and includes host and general indices.
Holsten, E.H.; Burnside, R.E.; Seybold, S.J. 2001. Verbenone interrupts the response to aggregation pheromone in the northern spruce engraver, Ips perturbatus (Coleoptera: Scolytidae), in south-central and interior Alaska. Journ. Ent. Soc. of British Columbia Vol. 98: 25-29.
Abstract: Addition of 84%-(-) verbenone at a high release rate to the three-component aggregation pheromone of Ips perturbatus significantly reduced trap catches.
For more information contact:
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Ed Holsten, Forest Entomologist |
