Forest Service 

Eastern Larch Beetle 

S.J. Seybold1, M.A. Albers2, and 

S.A. Katovich3

 

1

 Assistant Professor, Departments of 

Entomology and Forest Resources, 

University of Minnesota, St. Paul, MN, 

55108. 

2

 Forest Health Specialist, Minnesota 

Department of Natural Resources, Grand 

Rapids, MN, 55744. 

3

 Forest Entomologist, U.S. Department of 

Agriculture, Forest Service, St. Paul, MN, 

55108. 

The eastern larch beetle, D

simplex LeConte (fig. 1, 

native North American 

colonizes the phloem of the 

exposed roots, and larger 

tamarack, Larix laricina (

Koch. The adult beetles a

standing and fallen trees 

tunnel through the bark, a

mate in the phloem. Relati

Figure 1. Extensive mortality of tamarack caused by the eastern larch beet

Alaska. (Inset: Adult eastern larch beetle.) 
2 

injury or physiological stress from 

defoliation, mechanical damage, fire, 

drought, or flooding. 

Distribution and Hosts 

Eastern larch beetles can be found 

throughout the range of tamarack, 

which includes most of northeastern 

and north-central North America, 

western Canada, and Alaska (fig. 2). 

Two species of larch that are native to 

planted in an arboretum at th

Forestry Center in Minneso

Japanese larch, Larix k

(Lamb.) Carr., planted in the 

Kellogg Experimental Fo

Michigan; from Siberian lar

sibirica Ledeb., planted in a 

near Edmonton, Alberta; a

European larch, Larix decidua 

plantings near Wanakena, New 

The eastern larch beetle is a 

Figure 2. The geographic range of tamarack with collection records (dots) of ea

larch beetle reported by Bright (1976) and Wood (1982) and from the University 

Minnesota Insect Collection. The beetle is probably found throughout the range 

tamarack. 
3 

History of North American 

Infestations 

In eastern North America, the eastern 

larch beetle was reported infesting trees 

as early as 1897 (West Virginia), 1915 

(New York), 1926 (Quebec), and 1939 

(Nova Scotia). During the late 1970s 

and early 1980s, extensive outbreaks 

throughout that region resulted in 

mortality of nearly 600 million board 

feet (1.4 million m3 ) of tamarack. In 

the north-central region, eastern larch 

beetles were documented killing 

substantial numbers of trees as early as 

1883 (Ontario), 1888 (Michigan), and 

1938 (Minnesota). Notable outbreaks 

occurred in the 1960s (Ontario) and in 

the 1980s (Michigan and Minnesota). 

Most recently (2000-2001), eastern 

larch beetles killed large numbers of 

tamarack in northern Minnesota in 

stands that had no obvious history of 

defoliation, drought, or flooding injury. 

In western Canada, localized 

infestations have been reported since 

1946. In Alaska, tamarack mortality 

associated with the beetle occurred 

between 1974 and 1980 over an area of 

8 million acres (3.3 million ha) in the 

Tanana River Drainage and throughout 

the central portion of the State. In some 

areas of interior Alaska, 50 percent of 

the tamarack were killed in just over 2 

years; between 70 and 99 percent of the 

dead trees were in diameter classes 

greater than 4 inches (10 cm). 

averaging just over 1/12 inc

diameter, they are easily o

the trees show no othe

symptoms of attack. Red

boring dust may accumul

the entrance holes, but sin

the boring dust is left 

galleries, only small qu

boring dust will be expelle

entrance holes. The egg g

vertical tunnels that are w

sometimes branched (fig

galleries can be observed 

bark, slightly scoring th

They generally extend abo

inches (15 to 40 cm). E

from different females 

intersect. 

Figure 3. Eastern larch b

egg galleries. The vertica

galleries are slightly win

and sometimes branched 

(from Hopkins 1909). 
4 

the tree. 

From a distance, the most obvious 

evidence of current infestation is 

yellowing foliage that develops by late 

July or early August. Most trees begin 

to fade from the bottom, and it is 

common to see needles in the lower 

portion of the crown turning yellow, 

brown, and then falling off while the 

upper portion of the tree is still green. 

This can make it difficult to detect 

currently infested trees from the air. 

Not all infested trees will fade before 

the appearance of the normal fall color 

change. Infested trees generally fail to 

leaf out during the following spring. 

In fall and winter, woodpeckers often 

remove some or all of the bark from 

infested trees to search for and feed on 

overwintering larvae, pupae, and adults 

(fig. 4). In Minnesota, two species 

(black-backed, Picoides arcticus, and 

hairy, Dendrocopos villosus) of 

woodpeckers have been observed 

feeding on eastern larch beetle-infested 

trees. By late winter and early spring, 

bark removal reveals the beetle 

galleries and exposes the reddishpurple inner bark or white sapwood of 

the tree. Debarked trees can be quite 

obvious, especially when snow is on 

the ground, making it easy to identify 

infested trees from a distance. 

Identification of Life Stages 

Mature adults are dark brown with 

reddish-brown wing covers (elytra) 

(fig. 1, inset). Body length ranges from 

about 1/7 to 1/5 inch (3.4 to 5.0 mm). 

a taxonomic expert for 

confirmation. 

Eggs are white, oval to obl

small, about 1/25 inch (0.9 m

and about 1/50 inch (0.5 m

(fig. 5). Larvae are legless g

are white to whitish yellow 

colored), with a light brown 

6). They can be found under b

end of tunnels that extend aw

the larger egg gallery. Matu

are about 1/6 inch (4.5 m

Pupae are initially white to 

but darken as they prepare to 

to adults, and the pupae are 

Figure 4. Infested tamarack d

by woodpeckers. 
5 

 Figure 5. Eastern larch beetle eggs. 

 Figure 6. Eastern larch beetle larva. 

 Figure 7. Eastern larch beetle pupa. 

Life Cycle

Eastern larch beetles overwinter 

primarily in the adult stage beneath the 

bark of infested trees, but where winter 

temperatures permit survival, larvae 

April and June and fly to ne

where females colonize b

through the bark to th

Females produce an 

attractant that brings male

females to the coloniz

Arriving males may also 

chemical components to th

(pheromone). Each femal

within 1 or 2 days by a m

pair construct a vertical eg

the phloem by tunneling u

the entrance hole. Up to f

beetles may use the same e

to construct separate egg ga

Females lay up to four egg

or groove, and they lay an 

30 to 50 eggs per gallery. 

can develop from egg to ad

70 days. 

Before the new generatio

completely, 90 percent of 

parents can emerge from th

tree and initiate a second 

new tree. In warmer climat

percent of parents from 

brood tree may re-emerge 

third brood tree. Thus

considerable developmen

between the different brood

summer, and the later bro

more likely to overwinter as 

Nonetheless, there is 

generation per year, and 

Alaska, most newly for

remain in their brood gall

end of the summer to 

Some (30 to 40 percent) o

formed adults will emerge 
6 

Associated Insects 

Tamarack is a host for a variety of 

defoliating insects whose feeding may 

predispose trees to later successful 

attack by eastern larch beetles (see 

Stand Conditions Conducive to 

Infestation). In addition, other phloemfeeding bark beetles may co-occur with 

eastern larch beetles under the bark of 

western larch, and in rar

tamarack, in western North 

The adults of D. pseudots

similar in appearance to th

larch beetle, but are genera

and darker. Other bark beetles 

been reported infesting 

include the four-eyed spruc

Polygraphus rufipennis (Kir

8b); the balsam fir bark 

Figure 8. Insects associated with the eastern larch beetle (A) include the fou

eyed spruce beetle (B); the balsam fir bark beetle (C); and a checkered bee

(D). Bar in each photo = 1/25 inch (1 mm). Distinctive characters include 

bisected eye of four-eyed spruce beetle (inset B), and the spines on the wing 

covers of the male balsam fir bark beetle (inset C). 
7 

under the bark of infested trees. 

Stand Conditions Conducive to 

Infestation 

The stand conditions that are conducive 

to outbreaks of eastern larch beetles are 

poorly understood, and no rating 

systems are available to identify highrisk stands. Eastern larch beetles attack 

trees of almost any age or diameter 

class on the full range of sites from wet 

lowlands to drier uplands. Trees in pure 

stands as well as mixed stands are 

susceptible. However, many 

infestations are associated with trees 

under physiological stress, which can 

be from a variety of causes including 

defoliation, flooding, drought, cold 

soils, fire, old age, or damage from 

windstorms, snow breakage, or 

logging. 

Defoliation is considered to be the most 

common factor predisposing tamarack 

to attack by the eastern larch beetle. 

Outbreaks or damage by defoliating 

insects such as the larch sawfly, 

Pristiphora erichsonii (Hartig), the 

spruce budworm, Choristoneura 

fumiferana (Clemens), and the larch 

casebearer, Coleophora laricella

(Hübner), have all been reported to 

precede eastern larch beetle 

infestations. Moderate to severe 

defoliation by these insects, primarily 

in northeastern North America, has 

generally occurred 1 to 3 years prior to 

eastern larch beetle infestations. In 

1975 and 1976 in Alaska, severe 

defoliation by a larch bud moth, 

construction or beaver a

alters water flow. Floodi

tamarack trees outright a

produce abundant breedin

Tamarack trees have sh

systems so drought can 

substantial stress. In 

windthrow is more likely in 

with shallow root system

beetle breeds successfull

damaged in storms. It a

breeds in logging debris. T

tree age plays in creating p

stress in tamarack is 

documented. However, a

stands age, they likely be

susceptible to bark beetl

because tamarack trees are 

very intolerant of shade, 

competition may increase 

close in older stands. 

Although stressed stands 

storm and logging debris 

trigger many outbreaks

outbreaks have been asso

obvious stressors. Eastern l

appear to be capable of at

killing trees when no p

condition or factor is appare

Management Strategies 

Tamarack has not been 

managed, and therefore f

management strategies dire

at the eastern larch beetle 

evaluated. However, stra

revolve around pract

emphasize sanitation and o

health should reduce the l

significant tree mortality. 
8 

logs and utilization of material larger 

than 4 inches (10 cm) in diameter 

should reduce breeding material. This 

beetle has a 1-year life cycle with most 

progeny emerging in the spring. Thus, 

infested trees, logs and/or slash should 

be removed before warm spring 

weather. The timing of these activities 

becomes crucial because access to 

many tamarack stands is limited to the 

winter when wet soils are frozen. 

Silvicultural Methods: 

No studies have been done to evaluate 

silvicultural practices in tamarack 

stands and the response of eastern larch 

beetles to them. Thinning tamarack 

stands has not been a common forest 

management practice, but thinning 

other conifer species to improve tree 

vigor has proven to be beneficial 

against other bark beetle species. 

However, because tamarack trees have 

a shallow root system, damage to roots 

during thinning operations and 

windthrow of residual trees would be a 

concern. At the landscape level, 

harvesting or planting to create a 

diversity of stand ages may prove 

beneficial. In many areas, tamarack 

stands are all about the same age. 

Trap trees (green trees cut or girdled 

just before beetle flight in the spring) 

have been used successfully with other 

bark beetle species. They are quickly 

infested by the emerging adults and 

thus can act as a trap if removed before 

parents are likely to have re

and some (at least 30 to 40 p

the new adult beetle popul

likely to have re-emerged from 

trees in the late summer an

overwinter at the base of live t

Chemical Methods: 

The aggregation pheromone 

eastern larch beetle may be a 

management tool to monitor p

maximum flight activity, to 

increases in population density

mass trap the dispersing adults

most Dendroctonus spec

attractant is a blend of insect-

and host tree odors. In field 

Alaska and Minnesota, a ph

component called seudenol 

isolated from D. simplex, bu

from D. pseudotsugae) has p

be highly attractive when 

with host odors such as alph

These commercially 

attractants can be used as 

insect traps or in combinat

moribund or fallen trees in a b

tree strategy. 

Insecticides can be applied to 

of uninfested trees to kill 

adults. However, this i

warranted for forest trees, but 

utilized for individual high-v

at recreation sites or in la

Once trees are infested, 

control is no longer an 
9 

Assistance 

More information about the 

management of the eastern larch 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 eastern larch beetle. 

References 

Bright, D.E. 1976. The insects and 

arachnids of Canada. Part 2: The 

bark beetles of Canada and Alaska, 

Coleoptera: Scolytidae. Canada Dept. 

of Agriculture, Research Branch, 

Biosys-tematics Research Institute, 

Publication 1576. 241 p. 

Furniss, M.M. 1976. Controlled 

breeding, comparative anatomy and 

bionomics of Dendroctonus simplex

LeConte and Dendroctonus 

pseudotsugae Hopkins (Coleoptera: 

Scolytidae). pp. 109-120, in W.F. 

Barr (ed.), University of Idaho, 

Department of Entomology 

Anniversary Publication 15. 

Hopkins, A.D. 1909. Contributions 

toward a monograph of the scolytid 

beetles. I. The genus Dendroctonus. 

USDA Bureau of Entomology 

Technical Bulletin 17. 164 p. 

Emergence, host attack, a

overwintering behavior o

larch beetle, Dendroctonu

LeConte (Coleoptera:Sco

Newfoundland. The Cana

Entomologist. 119:975-9

Langor, D.W.; Raske, A.G. 

Reproduction and develop

eastern larch beetle, Dend

simplex LeConte 

(Coleoptera:Scolytidae), 

Newfoundland. The Cana

Entomologist. 119:985-99

Langor, D.W.; Raske, A.G. 

Mortality factors and life 

the eastern larch beetle, 

Dendroctonus simplex (C

Scolytidae), in Newfound

Environmental Entomolo

963.

Langor, D.W.; Raske, A.G. 

eastern larch beetle, anoth

our forests (Coleoptera: S

Forestry Chronicle. 65:27

Langor, D.W.; Raske, A.G. 

history of the eastern larc

Dendroctonus simplex (C

Scolytidae), in North Am

Lakes Entomologist. 22:1

Prebble, M.L. 1933. The lar

development of three bark 

The Canadian Entomolog

150. 

Werner, R.A. 1986. The eas

beetle in Alaska. USDA F

Service, Research Paper P

13 p. 
10 

 Figure 9. Eastern larch beetle (from Hopkins 1909) 
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