Spruce Budworm, Eastern United States

Forest Insect 

& Disease 

Leaflet 160 

U.S. Department 

of Agriculture 

Forest Service

Spruce Budworm in the Eastern United States

Daniel R. Kucera11 and Peter W. Orr2

1 Entomologist, State & Private Forestry, U.S. Department of Agriculture, Forest Service, Broomall, Pennsylvania.

2Staff entomologist, State & Private Forestry, U.S. Department of Agriculture, Forest Service, Washington, D.C.

Figure 1 

- Mature 

larva of 

the 

spruce 

budworm.

The spruce budworm Choristoneura 

fumiferana (Clemens) is one of the most destructive native 

insects in the northern spruce and fir forests of the Eastern United States and Canada. 

Periodic outbreaks of the spruce budworm are a part of the natural cycle of events 

associated with the maturing of balsam fir. 

The first recorded outbreak of the spruce budworm in the United States occurred in 

Maine about 1807. Another outbreak followed in 1878. Since 1909 there have been waves of 

budworm out breaks throughout the Eastern United States and Canada. The States most often 

affected are Maine, New Hampshire, New York, Michigan, Minnesota, and Wisconsin. These 

outbreaks have resulted in the loss of millions of cords of spruce and fir. 

Balsam fir is the species most severely damaged by the bud-worm in the Eastern United States. 

White, red, and black spruce are suitable host trees and some feeding may occur on tamarack, 

pine, and hemlock. Spruce mixed with balsam fir is more likely to suffer budworm damage than 

spruce in pure stands. 

The range of the spruce bud-worm includes the Northern States east of Montana but the budworm 

is found wherever host species grow (fig. 2).

Figure 2- Distribution of the Spruce budworm in the Eastern 

United States coincides with the range of balsam fir and 

spruce.

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Spruce Budworm, Eastern United States

Damage and Evidence of Infestation

Figure 3- Balsam fir needles 

mined by spruce budworm 

larvae

The newly hatched budworm larva is very small and difficult to find 

because it bores into and feeds on needles or expanding buds. These 

larvae can cause severe damage to the expanding buds. As the larva 

grows, needles are severed at the base and left hanging in a thin 

silken web. The severed needles turn brown, giving the defoliated 

tree a scorched appearance (fig. 3). This condition is apparent from 

about mid-June until late August, depending on the weather and 

latitude. 

Figure 4 - Severely defoliated 

balsam fir (left); red spruce 

with slight defoliation (right).

Early in an epidemic, defoliation is 

usually most noticeable in the top 

portion of the crown. After several 

years of heavy defoliation, the forest 

turns gray as dead tops become 

conspicuous (fig. 4). Individual trees die 

after 1 or more years of heavy 

defoliation, depending on their general 

vigor. 

Description

Figure 5- An adult spruce 

budborm

The adult moth has a wing span of 2 centimeters. It is usually grayish 

with dark brown markings (fig. 5). Some moths are brown or reddish 

with gray markings. Males and females occur in about equal numbers. 

Figure 6- Egg mass of the 

spruce budworm.

The light green eggs are about 1 millimeter 

long by 0.2 millimeter wide. The eggs, laid 

in elongate masses of 2 to 60 - averaging 

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Spruce Budworm, Eastern United States

about 20, overlap one another (fig. 6). 

Larvae go through six instars. The first 

larval instar, about 2 millimeters long, is 

yellowish green with a light- to mediumbrown head. The second instar is yellow 

with a dark brown or black head. During 

the next four in-stars, the body of the larva 

changes from a pale yellow to a dark 

brown with light-colored spots along the back. In the sixth instar, the 

larva is about 2.5 centimeters long and the head is dark brown or shiny 

black. The pupa is pale green at first, later changing to reddish brown. 

It is marked with darkened bands and spots (fig. 7). 

Figure 7- Pupa of the spruce budworm.

Life History and Habits

There is one generation of the spruce budworm each year. The female moth lays eggs on the flat 

undersurface of balsam fir or spruce needles, generally within 3 inches of the buds or defoliated 

area. In extremely high populations, eggs may be laid on almost any surface. Eggs are distributed 

more evenly on foliage of host trees in the Northeastern United States and eastern Canada than on 

those of western species. The eggs hatch in about 2 weeks. Usually, newly hatched larvae 

immediately seek a suitable place to spin their hibernacula or cocoon-like shelters. However, during 

warm periods, larvae may move about and feed on needles before spinning a hibernaculum. In 

doing so, they may spin down from a branch on a silken thread and be carried away by air 

currents. Larval dispersal at this stage is one means of spread within and beyond the infested 

stands. The young larva transforms into the second instar or stage within the hibernaculum and 

remains dormant over the winter. Old staminate flower bracts are preferred as overwintering sites, 

but bud scales and bark crevices are also used. 

In the spring-after several days of warm weather, but before the balsam fir buds begin to expand - 

the larva emerges from hibernation and begins feeding. Early feeding is first confined to the new 

buds of staminate flowers if present, or the larva mines the previous year's needles if staminate 

flowers are scarce. The new flower buds provide a ready source of food before the vegetative buds 

expand. The early emerging larvae that feed on staminate flower buds grow much more rapidly 

and have a higher survival rate than those that feed on old needles. 

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Spruce Budworm, Eastern United States

The larva migrates to the end of a twig and bores into a needle or an expanding vegetative bud. 

Some larvae spin down on silken threads and, as first instar larvae, may be dispersed by air 

currents. The larvae feeding on staminate flower buds and flowers stay in place until the 

immediate food supply is depleted. Later, the larva feeds on the new foliage of developing shoots. 

When the larva is in the fifth instar, it begins tying the tips of twigs together with silk, forming a 

small nest. The new foliage is eaten first. In epidemic situations, old needles and bark (near branch 

tips) may also be consumed to such a degree that branch tips and terminal shoots are destroyed. 

During late June through mid-July, depending on the weather, the larva completes development 

and stops feeding. 

The larva then transforms to a pupa, generally within the last-formed webbing. Some pupae are 

found at the axils (needle base) of the twigs. The moth emerges about 10 days later (in late June 

through mid-July). Peak moth flight activity occurs from about 7:30 p.m. to 11:30 p.m. Moths may 

be carried up to 10 miles or more by winds and can be transported hundreds of miles by storm 

fronts. 

Natural Control

The spruce budworm has a high reproductive capacity, but natural factors such as adverse 

weather, diseases, predators, and parasites play an important part in holding budworm populations 

in check. For example, high rates of parasitism of mature larvae by tiny parasitic wasps such as 

Meteorus trachynotus Viereck and 

Phaeogenes hariolus (Cresson) and by a tiny 

parasitic fly, Lypha setifacies (West), were seen in a 

declining budworm population in Maine and New York. But several successive years of favorable 

weather (warm, dry springs), adequate food, and suitable hibernation sites can lead to an outbreak 

beyond the control of these and other natural agents. Once a spruce budworm outbreak begins, it 

usually continues until the larvae consume much of the available foliage. As a result, the use of 

biological and chemical insecticides may be necessary to supplement natural control agents. 

Integrated Pest Management

The use of various tactics, such as biological insecticides, silvicultural practices, and chemical 

insecticides, in combination, is termed integrated pest management. For forest landowners, several 

tactics may be available, while the homeowner with only one or two trees has more limited 

options. A discussion of various management and control techniques follows. 

Biological control agents - 

Recent developments in the use of diseases as biological control agents hold some promise for 

spruce budworm control. At the present time, biological insecticides are more expensive than 

conventional chemical insecticides. In 1948, a polyhedral virus disease was reportedly found in 

budworm populations. The infectious nature of this disease was later demonstrated. With few 

exceptions, budworm larvae that were fed polyhedra showed effects of the disease within 72 

hours. However, many larvae survived, indicating that the virus was not particularly deadly. At 

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Spruce Budworm, Eastern United States

least four viruses are known to be endemic in North America (nucleopolyhedrosis, granulosis, 

cyloptasmic polyhedrosis, and entomopox). However, the current cost of applying a virus such as 

the nucleopolyhedrosis virus is about 30 times as expensive as applying chemical insecticides. 

A microsporidian disease, Perezia fumiferanae

Thomson, slows the rate of budworm development during the larval and pupal stages. The lifespan 

of infected adults is shortened. Females are affected more than males. To date, neither viruses nor 

fungi have provided sufficient control in field trials. 

Both field tests and operational applications of the bacterial pathogen 

Bacillus thuringiensis (B.t.) effectively 

controlled moderate populations of less than 50 larvae per 18-inch branch. However, in extreme 

populations of more than 8,000 egg masses per 100 square feet of foliage, B. t. did not protect 

foliage or reduce the population significantly. 

Indirect control - Budworm outbreaks develop and 

gain momentum in the Northeastern United States only when there is a large proportion of mature 

and overmature balsam fir in the forest. Management practices including a greater use of balsam 

fir, regulating age classes to prevent the occurrence of over-mature balsam fir over large areas, 

and favoring or planting less susceptible species such as spruce make conditions generally 

unfavorable to the budworm and may materially reduce the risk of an outbreak. 

In the Lake States, young balsam fir trees (1.5- to 4.6-m tall) growing next to mature balsam fir or 

white spruce stands often support heavy overwintering populations of the budworm. Vegetative 

buds, mined by spruce budworm larvae previously blown in or dropped from the overstory balsam 

fir, provide suitable hibernation sites for the next generation. Larvae are able to survive the winter 

and continue the infestation on these young trees the following year. One way to prevent 

infestations in young trees growing under a mature balsam fir and white spruce overstory is to 

remove the overstory trees and replant the stand with non-susceptible species such as white pine. 

Insecticides can be applied to adjoining mature stands to protect the young stands nearby. 

Direct control -Application of chemical or biological 

insecticides is the most economical way to prevent widespread damage caused by heavy budworm 

populations. Aerial spraying of registered insecticides satisfactorily controls larvae and, when 

applied against early instars, provides effective foliage protection. Among the registered 

insecticides in addition to B.t. are carbaryl, trichlorfon, acephate, malathion, and 

fenitrothion. Several insecticides are registered for use under the supervision of licensed 

applicators. B.t. and fenitrothion are registered for use only in the Eastern United 

States. Therefore, appropriate State forestry agencies or the U.S. Department of Agriculture, Forest 

Service, should be consulted for further details before applying insecticides for budworm control. 

Special care must be taken when treating infested stands near streams and lakes or other 

environmentally sensitive areas. 

Figure 8- Color infared photo of 

a treated white spruce 

Spraying does not kill all the larvae because some are protected by 

the webbed foliage within which they are feeding. An accurately 

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Spruce Budworm, Eastern United States

plantation: the spray swath is 

next to the road in left of 

photo. 

performed application of a registered insecticide will reduce larval 

populations sufficiently to retain 35 or more percent of the foliage 

(fig. 8). This is enough to keep trees alive, or until they can be 

harvested. 

Caution: Pesticides used improperly can be injurious to man, 

animals, and plants. Follow the directions and heed all precautions 

on the 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 when there is danger of drift, when honey bees or other pollinating 

insects are visiting plants, or when they may contaminate water or leave illegal residues. 

Avoid prolonged inhalation of pesticide sprays or dusts; wear protective clothing and equipment if 

specified on the container. 

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. 

Do not clean spray equipment or dump excess spray material near ponds, streams, or wells. 

Because it is difficult to remove all traces of herbicides from equipment, do not use the same 

equipment for insecticides or fungicides that you use for herbicides. 

Dispose of empty pesticide con tainers promptly. Have them buried at a sanitary landfill dump or 

crush and bury them in a level, isolated place. 

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 En 

vironmental Protection Agency, consult your county agricultural agent or State extension specialist 

to be sure the intended use is still registered. 

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