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''Choristoneura fumiferana'', the eastern spruce budworm, is a species of moth of the family
Tortricidae The Tortricidae are a family of moths, commonly known as tortrix moths or leafroller moths, in the order Lepidoptera. This large family has over 11,000 species described, and is the sole member of the superfamily Tortricoidea, although the genu ...
native to the eastern United States and Canada. The caterpillars feed on the needles of spruce and fir trees. Eastern spruce budworm populations can experience significant oscillations, with large outbreaks sometimes resulting in wide scale tree mortality. The first recorded outbreaks of the spruce budworm in the United States occurred in about 1807, and since 1909 there have been waves of budworm outbreaks throughout the eastern United States and Canada. In Canada, the major outbreaks occurred in periods circa 1910–20, c. 1940–50, and c. 1970–80, each of which impacted millions of hectares of forest. Longer-term tree-ring studies suggest that spruce budworm outbreaks have been recurring approximately every three decades since the 16th century, and paleoecological studies suggest the spruce budworm has been breaking out in eastern North America for thousands of years. Budworm outbreaks can have significant economic impacts on the forestry industry. As a result, the eastern spruce budworm is considered one of the most destructive forest pests in North America, and various methods of control are utilized. However, the species is also ecologically important, and several bird species are specialised on feeding on budworms during the breeding season. Several theories exist to explain the cyclical budworm outbreaks.


Taxonomy

Clemens Clemens is both a Late Latin masculine given name and a surname meaning "merciful". Notable people with the name include: Surname * Adelaide Clemens (born 1989), Australian actress. * Andrew Clemens (b. 1852 or 1857–1894), American folk artist ...
originally named the eastern spruce budworm, ''C. fumiferana'', in 1865, which was recognized as a Nearctic representative of the genus C''horistoneura''.Freeman, T.N. 1947. A new generic assignment for'' Archips fumiferana'' (Clemens), the spruce budworm. Can. Entomol. 79:21. At this time, the name applied to populations in a variety of geographic regions and
biotope A biotope is an area of uniform environmental conditions providing a living place for a specific assemblage of plants and animals. ''Biotope'' is almost synonymous with the term "habitat", which is more commonly used in English-speaking countri ...
s. The '' C. pinus,'' a distinct form of the ''Choristoneura,'' was later established as a separate species. However, a large group of this genus in the western part of North America remained taxonomically undefined as the "western complex"Freeman, T.N. 1953
The spruce budworm ''Choristoneura fumiferana'' (Clem.) and an allied new species on pine (Lepidoptera: Tortricidae)
Can. Entomol. 85:121–127.
until T.N. Freeman established several new species in 1967. Field collections of late instar larvae of ''Choristoneura'' populations were taken from a range of localities in a wide arc, from the
Atlantic seaboard The East Coast of the United States, also known as the Eastern Seaboard, the Atlantic Coast, and the Atlantic Seaboard, is the coastline along which the Eastern United States meets the North Atlantic Ocean. The eastern seaboard contains the co ...
along the edge of the Laurentian Shield to the Mackenzie River area near the
Arctic Ocean The Arctic Ocean is the smallest and shallowest of the world's five major oceans. It spans an area of approximately and is known as the coldest of all the oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, a ...
. From these collections, only points east of the Rocky Mountain foothills yielded ''C. fumiferana.'' The two-year-cycle budworm '' C. biennis'' occurs only in the
subalpine Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures fall as elevation increases, causing the ecosystem to stratify. This stratification is a crucial f ...
forest region,Rowe, J.S. 1959
Forest regions of Canada
Ottawa, Dept. Northern Affairs & National Resources, Forestry Branch. 71 p.
Halliday, W.E.D. 1937
A forest classification for Canada
Can. Dep. Mines and Resources, Dominion For. Serv., Ottawa ON, Bull. 89. 50 p.
with
alpine fir Alpine may refer to any mountainous region. It may also refer to: Places Europe * Alps, a European mountain range ** Alpine states, which overlap with the European range Australia * Alpine, New South Wales, a Northern Village * Alpine National P ...
and interior spruce as hosts. Budworm populations from
Rocky Mountain The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico in ...
regions south of the area of
introgressive hybridization Introgression, also known as introgressive hybridization, in genetics is the transfer of genetic material from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species. Introg ...
of spruce differ from ''C. biennis''. Other budworms are of little or no consequence with respect to spruces.


Range and habitat

The range of the eastern spruce budworm is the largest of all budworms and coincides with the range of its hosts: fir and spruce trees in eastern North America, primarily in Canada. It includes the
Boreal Forest Taiga (; rus, тайга́, p=tɐjˈɡa; relates to Mongolic and Turkic languages), generally referred to in North America as a boreal forest or snow forest, is a biome characterized by coniferous forests consisting mostly of pines, spruce ...
as well as the Great Lakes-St. Lawrence, Northern, and
Acadian The Acadians (french: Acadiens , ) are an ethnic group descended from the French who settled in the New France colony of Acadia during the 17th and 18th centuries. Most Acadians live in the region of Acadia, as it is the region where the des ...
forest regions.Sanders, C.J. 1991
"Biology of North American spruce budworms"
p. 579–520 ''in'' van der Geest, L.P.S.; Evenhuis, H.H. (Eds.). Tortricid Pests, their Biology, Natural Enemies and Control. Elsevier Science, Amsterdam ordrecht The Netherlands.
This range extends westward to Alaska. The spruce budworm is commonly found in
boreal Boreal may refer to: Climatology and geography *Boreal (age), the first climatic phase of the Blytt-Sernander sequence of northern Europe, during the Holocene epoch *Boreal climate, a climate characterized by long winters and short, cool to mild ...
and sub-boreal forest regions, specifically those that consist of
spruce-fir forests A spruce is a tree of the genus ''Picea'' (), a genus of about 35 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal ( taiga) regions of the Earth. ''Picea'' is the sole genus in the subfa ...
.


Food resources


Host plant preferences

The main hosts of the eastern spruce budworm in eastern North America are
balsam fir ''Abies balsamea'' or balsam fir is a North American fir, native to most of eastern and central Canada (Newfoundland west to central Alberta) and the northeastern United States (Minnesota east to Maine, and south in the Appalachian Mountains to W ...
,
white spruce White spruce is a common name for several species of spruce (''Picea'') and may refer to: * ''Picea glauca'', native to most of Canada and Alaska with limited populations in the northeastern United States * ''Picea engelmannii ''Picea engelman ...
, and
black spruce ''Picea mariana'', the black spruce, is a North American species of spruce tree in the pine family. It is widespread across Canada, found in all 10 provinces and all 3 territories. It is the official tree of the province of Newfoundland and Labra ...
,Swaine, J.M.; Craighead, F.C.; Bailey, J.W. 1924. Studies on the spruce budworm ''Cacoecia fumiferana'' Clem. Can. Dep. Agric., Ottawa ON, Tech. Bull. 37 (N.S.).Balch, R.E.; Webb, F.E.; Morris, R.F. 1954
Results of spraying against spruce budworm in New Brunswick
Can. Dep. Agric., For. Biol. Div., Ottawa ON, Bi-mo. Progr. Rep. 10(1).
but the larvae feed almost exclusively on current-year needles of balsam fir and white spruce. In massive outbreaks, populations of the insect can become so high that the larvae will feed on old foliage after the current-year foliage has been depleted.Belyea, R.M. 1952
Death and deterioration of balsam fir weakened by spruce budworm defoliation in Ontario
J. For. 50:729–738.
Traditionally, the eastern spruce budworm prefers balsam fir over white spruce.Ives, W.G.H.; Wong, H.R. 1988
Tree and shrub insects of the prairie provinces
Gov’t Can., Can. For. Serv., Edmonton AB, Inf. Rep. NOR-X-292. 327 p.
oates et al. 1994 Oates may refer to: ;People * Oates (surname) * Garfunkel and Oates, comedy act ** Kate Micucci (aka ''Oates'') of "Garfunkel and Oates" *Hall & Oates, musical act ;Places and buildings * Oates, Missouri, a community in the United States * Oates ...
/ref>Bichon, R. 1995. Canopy population and late instar dispersal of eastern spruce budworm: balsam fir versus white spruce. p. 25 ''in'' Carroll, A.L. and Raske, A.G. (Ed./Comp.). Proc. Eastern Spruce Budworm Research Conference, St. John’s NL, April 1994. However, one study showed contradicting evidence. In this study, Bichon sampled spruce budworm populations on branches from the upper mid-crowns of dominant or co-dominant balsam fir and white spruce. This was done at 20 randomly selected points in the Black Sturgeon Lake area near Thunder Bay, Ontario. The number of late-instar larvae captured in water traps was recorded throughout the dispersal period of the late instar larvae. The data indicated that white spruce canopies contained 2 to 3 times more spruce budworm than balsam fir canopies. A similar pattern was found in the understory. Water traps under white spruce trees captured more than 3 times as many larvae as did those under balsam fir trees for most of the dispersal period.


Impact on hosts

Balsam fir is the most susceptible host to outbreaks of the spruce budworm. Annual defoliation of current-year growth for 5 to 8 years will kill the host tree. Defoliation by the spruce budworm is most clearly reflected in the fir's radial growth. The population of mature balsam fir in a forest is greatly reduced by a combination of factors: its shorter lifespan and a great vulnerability to lethal budworm attacks.Blais, J.R.; Archambault, L. 1982
Rating vulnerability of balsam fir to spruce budworm attack in Quebec
Can. For. Serv., Ste.-Foy QC, Inf. Rep. LAU-X-51. 19 p.
The dietary preference for balsam fir over white spruce has the potential to alter the structure and composition of spruce-fir forests. Similarly, the next-generation
stand Stand or The Stand may refer to: * To assume the upright position of standing * Forest stand, a group of trees * Area of seating in a stadium, such as bleachers * Stand (cricket), a relationship between two players * Stand (drill pipe), 2 or 3 j ...
of trees are influenced by the late instar larvae that disperse to the understory of the forest and feed on the regeneration of plants. During a 1957 budworm outbreak in Quebec, balsam fir mortality was greater than 75% in stands in which no mortality was reported among the smaller component of white spruce. However, while balsam fir is the preferred host, severe outbreaks have occurred among white spruce stands in the
Prairie Provinces The Canadian Prairies (usually referred to as simply the Prairies in Canada) is a region in Western Canada. It includes the Canadian portion of the Great Plains and the Prairie Provinces, namely Alberta, Saskatchewan, and Manitoba. These provin ...
and Northwest Territories containing little or no balsam fir. The white spruce is less susceptible to budworm attack but can experience extreme defoliation during severe outbreaks. Young white spruce and black spruce trees that had been transplanted to cleared areas became infested with dozens of late-stage larvae during severe outbreaks in north-central Ontario.Sutton, R.F. 1982
Plantation establishment in the boreal forest: planting season extension
Can. Dep. Environ., Can. For. Serv., Sault Ste. Marie ON, Inf. Rep. O-X-344. 129 p.
Mortality among white spruce also occurred in northwestern Ontario and the
Algoma District Algoma District is a district and census division in Northeastern Ontario in the Canadian province of Ontario. The name was created by an American ethnologist, Henry Rowe Schoolcraft (1793-1864), who was appointed Indian agent to the Ojibwe in ...
of Ontario, as well as in certain areas of New Brunswick.Blais, J.R. 1976
Preliminary observations on the vulnerability of white spruce to spruce budworm defoliation in western Quebec
Environ. Can., Can. For. Serv., Ottawa ON, Bi-mo. Res. Notes 32(2):10–11.
Significant damage is also caused to
subalpine fir ''Abies lasiocarpa'', the subalpine fir or Rocky Mountain fir, is a western North American fir tree. Description ''Abies lasiocarpa'' is a medium-sized evergreen conifer with a very narrow conic crown, growing to tall, exceptionally , with a t ...
.Harvey, G.T. 1985
The taxonomy of the coniferophagous ''Choristoneura'' (Lepidoptera: Tortricidae): a review
p. 16–48 ''in'' Sanders C.J., Stark, R.W., Mullins, E.J.; Murphy, J. (Eds.). Recent Advances in Spruce Budworms Research. CANUSA Spruce Budworms Research Symp. Proc., Bangor ME, Sept. 1984. Can For. Serv./USDA For. Serv., Ottawa ON.
Red spruce ''Picea rubens'', commonly known as red spruce, is a species of spruce native to eastern North America, ranging from eastern Quebec and Nova Scotia, west to the Adirondack Mountains and south through New England along the Appalachians to western ...
, in its limited distribution, and tamarack are also attacked.Sippell, W.L. 1983
A review of the spruce budworm and its outbreak history
p. 17–25 ''in'' Sanders, C.J.; Carrow, J.R. (Eds.). The spruce budworm problem in Ontario – real or imaginary? Can.–Ont. Joint For. Res. Committee Sympos., Timmins ON, Sept. 1982. COJFRC Sympos. Proc. O-P-11.


Food shortage

Food shortages can occur in budworm populations if the budworms kill a significant amount of trees in the stand, such as during outbreaks. When food becomes depleted, the larvae feed on old foliage, which will result in slowed development and reduced fecundity in the female moths. However, food shortages generally do not lead to larval mortality.


Microbiome

The midgut microbiota of the spruce budworm larvae is primarily composed of Pseudomonadota, mainly from the genus ''Pseudonomas''. Two specific species from this genus are ''
P. fluorescens ''Pseudomonas fluorescens'' is a common Gram-negative, rod-shaped bacterium. It belongs to the ''Pseudomonas'' genus; 16S rRNA analysis as well as phylogenomic analysis has placed ''P. fluorescens'' in the ''P. fluorescens'' group within the genu ...
'' and '' P. paea''. '' Enterococcus'' and '' Staphylococcus'' bacteria were found in lower abundance as well. Diet plays a role in influencing the gut microbiome. One study found possible negative consequences of ingesting balsam fir as it may release juices that adversely affect the midgut microbiota.


Reproduction and life cycle


Mating


Pheromones and mate choice

As with other species in the genus ''Choristoneura'', spruce budworm females produce
sex pheromones Sex pheromones are pheromones released by an organism to attract an individual of the same species, encourage them to mate with them, or perform some other function closely related with sexual reproduction. Sex pheromones specifically focus on i ...
to attract males as potential mates and enhance their base level of sexual activity. ''C. fumiferana'' females emit
aldehyde In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl group ...
s, using a 95:5 mix of ''E-'' and ''Z''11-tetradecenals (''E''/''Z''11-14Ald) while some other species of ''Choristoneura'' emit
acetate An acetate is a salt formed by the combination of acetic acid with a base (e.g. alkaline, earthy, metallic, nonmetallic or radical base). "Acetate" also describes the conjugate base or ion (specifically, the negatively charged ion called an ...
s and
alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...
s. The pheromone is made with
palmitate Palmitic acid (hexadecanoic acid in IUPAC nomenclature) is a fatty acid with a 16-carbon chain. It is the most common saturated fatty acid found in animals, plants and microorganisms.Gunstone, F. D., John L. Harwood, and Albert J. Dijkstra. The L ...
using
β-oxidation In biochemistry and metabolism, beta-oxidation is the catabolic process by which fatty acid molecules are broken down in the cytosol in prokaryotes and in the mitochondria in eukaryotes to generate acetyl-CoA, which enters the citric acid cyc ...
and Δ11-desaturation and stored as unsaturated ''E''/''Z''11-14Ac. Male size is an important factor in reproductive success, but male ''C. fumiferana'' also emit a pheromone that helps attract females. This pheromone becomes available through larval and adult feeding. While attempting to copulate, males will exhibit their abdominal hair pencils to the female. These hair pencils release a volatile pheromone and play a role in attracting females. The chemical composition of the volatile pheromone is currently unknown. Some studies suggest that these pheromones are indicators of male mate quality and prevent other males from approaching the female. Females exhibit selective mate choice as they show more parental investment. Pheromones allow females to recognize and assess males as mates. Male ''C. fumiferana'' prefer to mate with virgin females.


Copulation

Female ''C. fumiferana'' start accepting males for copulation early in the day, and a good number of females are active by sunset. Before attempting to mate, the male will spread its abdominal hairs and fan its wings as either the wing glands or the hairs have a scent to which females respond. The moths perform end-to-end mating with attached genitalia. Males will mate guard throughout prolonged copulation with the female. Mating lasts around 3 hours. Increased mating times are correlated with increased production of fertile eggs. When mating is interrupted, the ''C. fumiferana'' female may oviposit infertile eggs or resume mating with other males. Consecutive matings in male ''C. fumiferana'' lead to an overall decline in male reproductive performance: decreased spermatophore mass, increased mating time, and a smaller amount of sperm produced.


Nuptial gifts

Upon copulation, males transfer a
spermatophore A spermatophore or sperm ampulla is a capsule or mass containing spermatozoa created by males of various animal species, especially salamanders and arthropods, and transferred in entirety to the female's ovipore during reproduction. Spermatophore ...
containing its ejaculate and additional nutrients to the female, which functions as a
nuptial gift A nuptial gift is a nutritional gift given by one partner in some animals' sexual reproduction practices. Formally, a nuptial gift is a material presentation to a recipient by a donor during or in relation to sexual intercourse that is not simpl ...
. This gift is an important display of male investment because females may only have a few mature eggs to be fertilized upon emergence from the pupae. Male larval nutrition influences the quality, size, and weight of the spermatophore with increased nutrition having a positive effect. During outbreak periods when food is scarcer, larvae will feed on old foliage and receive less nutrition. Males that feed on young foliage have been found to grow bigger, produce larger spermatophores, and often have more success in attracting a female.


Oviposition

Female moths lay one brood per season, and eggs are laid over several days. The number of eggs per egg mass varies from 1 to about 60, but there are 20 eggs on average per mass. These masses are laid in 2 to 4 rows on conifer foliage, preferably balsam fir and spruce needles. Generally, females can lay 100 to 300 eggs in a lifetime but average approximately 200 eggs. These eggs hatch after around 10 days, but this period ranges from 8 to 12 days. The spruce budworm oviposits on needles of host trees in late June or mid-July to early August. Large numbers of egg masses are deposited on the peripheral shoots of the crown.


Host plant learning and selection for egg laying

''C. fumiferana'' females are
univoltine Voltinism is a term used in biology to indicate the number of broods or generations of an organism in a year. The term is most often applied to insects, and is particularly in use in sericulture, where silkworm varieties vary in their voltinism. ...
(laying one brood per year) and must make careful decisions about oviposition sites. Selection is based on chemical cues, shape, and structure of the cuticular wax on the site. Studies have shown that
sensilla A sensillum (plural ''sensilla'') is an arthropod sensory organ protruding from the cuticle of exoskeleton, or sometimes lying within or beneath it. Sensilla appear as small hairs or pegs over an individual's body. Inside each sensillum there are ...
important in detecting this information may be located on the moth's legs. When evaluating the host plant, the moth drums its forelegs against the surface and likely scratches the leaf with its tarsal claws on their feet, which releases compounds detected by the moth's
chemoreceptor A chemoreceptor, also known as chemosensor, is a specialized sensory receptor which transduces a chemical substance (endogenous or induced) to generate a biological signal. This signal may be in the form of an action potential, if the chemorecept ...
s. Unsuccessfully mated and virgin females are less adept at probing oviposition sites due to unactivated sensilla.


Life history


Egg

Eggs are light green in color and laid in several overlapping rows within masses on the host plant. They hatch 8–12 days after they are laid.


Caterpillar

After dispersal, first- instar caterpillars create hibernacula preferably inside flower bracts and beneath bark scales. They then molt to the second instar without feeding and
overwinter Overwintering is the process by which some organisms pass through or wait out the winter season, or pass through that period of the year when "winter" conditions (cold or sub-zero temperatures, ice, snow, limited food supplies) make normal activi ...
as second-instar larvae in
diapause In animal dormancy, diapause is the delay in development in response to regular and recurring periods of adverse environmental conditions.Tauber, M.J., Tauber, C.A., Masaki, S. (1986) ''Seasonal Adaptations of Insects''. Oxford University Press I ...
. The second-instar larvae emerge in early May and disperse to feed on seed, pollen cones, flower bracts, and needles at host trees, preferably the balsam fir. In June and July, larvae in third to sixth instars feed on current-year shoots then old foliage after the shoots are depleted. 90% of a larva's food consumption occurs after the sixth instar, which is when the most damage is caused to host trees. Young caterpillars are a cream color when they hatch. Late instar larvae have dark brown heads and prothoracic shields and are 3 centimeters long when fully developed. Their bodies are also dark brown but have light spots on the back.


Pupa

The pupae are formed in early July on foliage in the forests. Both sexes of ''C. fumiferana'' pupae are initially light green then later range in color from black to a reddish-brown. They are approximately 12 to 15 millimeters long.


Adult

The moths will emerge from the pupae within 8 to 12 days, during mid-June to August. Adult spruce budworm are medium-sized (15 mm in length) and dichromatic, exhibiting gray and rust colors. The wings have silvery patches and are 21 mm to 30 mm in wingspan. Peak activity occurs during the later afternoon and early evening. After emerging, the adults will mate and lay eggs in July or August. The lifetime of the ''C. fumiferana'' lasts around 2 years. Pupae last for around 10 days, and adult moths live for approximately 2 weeks. In one year, there is one generation of offspring.


Migration


Local or regional dispersal

After the eggs hatch, first-instar caterpillars will disperse from the oviposition site throughout the tree or stand using silk strands. They are sometimes carried further by the wind. In early May, the second-instar larvae emerge and disperse to host trees. The majority of larval mortality occurs during fall and spring dispersal. Eastern spruce budworm moths are strong fliers and disperse in exodus in the evening. They can fly at elevations over 100 meters before going to a new site, which is typically only 50 to 100 kilometers downwind, but can sometimes be up to 450 km away. After depositing some eggs at the first dispersion site, female moths may emigrate and lay eggs at multiple sites. Factors controlling budworm flight during dispersal include meteorological conditions and temperature. Moths will not disperse when the temperature is below 14°C or above 30°C. When the temperature drops below 14°C mid-flight, the moth will fold its wings and descend from the sky.


Long distance migration

Long distance migration of the spruce budworm does occur as they can disperse across distances ranging from 20 to 450 km. In northern Minnesota, spruce budworm moths emigrate to the east lakeshore of
Lake Superior Lake Superior in central North America is the largest freshwater lake in the world by surface areaThe Caspian Sea is the largest lake, but is saline, not freshwater. and the third-largest by volume, holding 10% of the world's surface fresh wa ...
in Ontario, Canada, because of seasonal changes. Dispersal is influenced heavily by temperature as low temperatures can slow down both take off and arrival. Other factors include dispersal direction, precipitation, altitude, and wind flow. It is likely that mass exoduses of the ''C. fumiferana'' over long distances are a result of food shortage in the local area.


Predators

Eastern spruce budworm egg masses are immobile and less vulnerable to predation than other stages of the cycle. Small larvae are exposed to predators during dispersal but become safer while bud or needle mining or overwintering in hibernacula. Large larvae actively escape predation by dropping from the tree foliage, which can also attract the attention of other predators. Predators outside of host plants on the forest floor include
ant Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of 22,0 ...
s, spiders,
beetle Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...
s, and small mammals. Pupae are vulnerable because the budworm are generally immobile in this state. The adult moths can fly away from predators but are then exposed to various birds, dragonflies, and
robber flies The Asilidae are the robber fly family, also called assassin flies. They are powerfully built, bristly flies with a short, stout proboscis enclosing the sharp, sucking hypopharynx. The name "robber flies" reflects their notoriously aggressive pr ...
. Spruce budworm male and female moths experience increased vulnerability during copulation.
Insectivorous A robber fly eating a hoverfly An insectivore is a carnivorous animal or plant that eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects. The first vertebrate insectivores we ...
birds are a common and major predator of the spruce budworm, mainly preying on the larvae and pupae. Examples of species include
sparrow Sparrow may refer to: Birds * Old World sparrows, family Passeridae * New World sparrows, family Passerellidae * two species in the Passerine family Estrildidae: ** Java sparrow ** Timor sparrow * Hedge sparrow, also known as the dunnock or hed ...
s, thrushes, and overstory
warbler Various Passeriformes (perching birds) are commonly referred to as warblers. They are not necessarily closely related to one another, but share some characteristics, such as being fairly small, vocal, and insectivorous. Sylvioid warblers The ...
s. Bird distribution will change to reflect budworm density in the forests. A 1989 study found that the highest populations of spruce budworm larvae and pupae occur in June and July. This coincides with the period when some species of birds require maximum food to feed their young. As a result, predation by birds helps control the growth of budworm predation. Other major predators include various invertebrates, primarily spiders. In spruce-fir forests throughout Maine, the late-instar spruce budworm larvae is preyed on by eumenid wasps such as the '' A. adiabatus'', and '' E. leucomelas''. This predation is important in controlling populations of the spruce budworm in forest stands. Spruce budworm larvae are attacked by parasitoids from the Hymenoptera and Diptera orders, which include common wasps such as '' Apanteles fumiferanae'' and '' Glypta fumiferanae''. First- and second-instar larvae are parasitized in the summer. When they are in their fourth or higher instars the next summer, the larvae are killed by the newly emerged wasps. Other species of parasitoid wasps (e.g. '' Meteorus trachynotus'') will attack the larvae when they are in their third to fourth instars, emerging during the sixth instar or from the pupae. About 90 parasitoids have been collected from spruce budworm in eastern North America. In 1996, Henry found that the suite of parasitoids collected from spruce budworm in isolated white spruce plantations of southern Ontario differed from the usual suite of parasitoids found in the
boreal forest Taiga (; rus, тайга́, p=tɐjˈɡa; relates to Mongolic and Turkic languages), generally referred to in North America as a boreal forest or snow forest, is a biome characterized by coniferous forests consisting mostly of pines, spruce ...
.Henry, B. S. 1996. Spruce budworm parasitoid investigations in southern Ontario white spruce plantations. MSc thesis, Univ. Guelph, Guelph ON. 187 p.


Physiology


Thermoregulation

Weather and variances in temperature can influence the larval development of the spruce budworm. During the cold winters, the larvae overwinter in their hibernaculae in true
diapause In animal dormancy, diapause is the delay in development in response to regular and recurring periods of adverse environmental conditions.Tauber, M.J., Tauber, C.A., Masaki, S. (1986) ''Seasonal Adaptations of Insects''. Oxford University Press I ...
until they can resume growth in the springtime. When the weather is warm in late fall and early spring, the budworm may metabolize at a higher rate, which depletes its finite food resources while in the hibernaculae. Harsher winters are associated with declines in population, even reaching 49% mortality. This is either due to the frigid temperatures or cumulative effect of the cold over time. Frost can be deadly to these early-instar larvae. Warm spring temperatures may also have multiple effects. After emergence, it may prompt more dispersal which increases mortality, but this is hard to determine. It is more likely to help development and increase survival. Overall, cold, wet temperature may be detrimental during this larval period while hot and dry summer weather is most favorable.


Diapause

During
diapause In animal dormancy, diapause is the delay in development in response to regular and recurring periods of adverse environmental conditions.Tauber, M.J., Tauber, C.A., Masaki, S. (1986) ''Seasonal Adaptations of Insects''. Oxford University Press I ...
, the ''C. fumiferana'' larvae have low metabolic activity and stalled developmental growth. After the first instar, they enter diapause and overwinter. Spruce budworms may overwinter twice, and thus enter diapause twice, when they are on a two-year life cycle. This can occur in the spruce-basalm forests of central and southern British Columbia and of the
Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico in ...
. Larvae have been observed to end the first diapause in the summer and develop slowly until they enter diapause as fourth-instar larvae. They then emerge the following spring and develop into adults by late July. Two-year life cycles typically occur in regions with low average daily temperatures and short, frost-free seasons. In general, diapause is environmentally determined.


Outbreaks

Paleoecological studies suggest the spruce budworm has been breaking out in eastern North America for thousands of years.


Theories

Populations of ''C. fumiferana'' can increase and decrease rapidly during short periods of time. Outbreaks occur as the population suddenly increases before crashing once again. According to one common theory (the double equilibrium hypothesis), popularized in the 1970s, periodic outbreaks of the spruce budworm are a part of the natural cycle of events associated with the maturing of balsam fir. A key point is that outbreak frequency cannot be predicted. The
catastrophe theory In mathematics, catastrophe theory is a branch of bifurcation theory in the study of dynamical systems; it is also a particular special case of more general singularity theory in geometry. Bifurcation theory studies and classifies phenomena c ...
of budworm outbreaks holds that particularly major infestations occur every 40–60 years, as the result of a cusp-catastrophe event, whereby populations jump suddenly from endemic to epidemic levels. An alternative theory holds that outbreaks are the result of spatially synchronized population oscillations that are caused by delayed density-dependent feedback (from various mortality agents) which are synchronized via a process of
entrainment Entrainment may refer to: * Air entrainment, the intentional creation of tiny air bubbles in concrete * Brainwave entrainment, the practice of entraining one's brainwaves to a desired frequency * Entrainment (biomusicology), the synchronization of ...
. Finally, the epicenter theory describes a model in which outbreaks begin at an epicenter and spread outward through dispersal. These epicenters have less destruction overall and tend to occur in the Great Lakes-St. Lawrence forest corridor. From these epicenters, the outbreak will spread and combine with other epicenters to create a larger epidemic.


Evidence

Balsam fir can provide evidence of outbreaks with its radial-growth data. However, it generally cannot be used to obtain information on outbreaks that occurred more than 75 years previously. White spruce is also particularly useful for providing evidence of past outbreaks of spruce budworm through radial-growth data. They can provide excellent records from as far back as 200, sometimes 300, years. Although the white spruce is more resistant to budworm attack than balsam fir, heavy defoliation can occur during severe outbreaks, which results in reduction of radial growth. In lesser outbreaks, radial growth is moderately reduced, which often makes it difficult to distinguish if it is caused by random or weather-related fluctuations. Comparisons between radial growth in host trees and non-host trees (especially white and red pines) are used to detect the budworm effect.Blais, J.R. 1985
The ecology of the eastern spruce budworm: a review and discussion
p. 49–59 ''in'' Sanders C.J.; Stark, R.W.; Mullins, E.J.; Murphy, J. (Eds.). Recent Advances in Spruce Budworms Research. CANUSA Spruce Budworms Research Symp. Proc., Bangor ME, Sept. 1984. Can For. Serv./USDA For. Serv., Ottawa ON.


Occurrences

Spruce budworm outbreaks usually first appear in localized areas before spreading to immense territories.Blais, J.R. 1961b
Aerial application of insecticides and the suppression of incipient budworm outbreaks
For. Chron. 37(3):203–210.
Population explosions can be astonishingly rapid. For example, in the Kedgwick Lake area of Quebec, egg sampling in summer 1959 had indicated that budworm populations would be low in 1960, but a much larger population developed in response to favorable weather and food conditions. Such situations are unlikely to recur frequently, but it is common for populations of larvae to be spread through wind dispersal. Unfavorable weather in the spring can strongly influence both budworm and host development.Blais, J.R. 1981a
Effects of late spring frosts in 1980 on spruce budworm and its host trees in the Laurentian Park region of Quebec
Can. For. Serv., Ottawa, ON. Res. Notes 1(3):16–17.
Luciuk, G.S. 1984
Effect of climatic factors on post-diapause emergence and survival of spruce budworm larvae (Lepidoptera: Tortricidae)
Can. Entomol. 116:1077–1083.
Massive outbreaks of spruce budworm occur irregularly throughout the range, but populations of this insect can remain at an endemic level for long periods. In 1943, a continuing outbreak in Ontario and western Quebec caused heavy mortality, particularly in stands of balsam fir. Half of the 25 million cords (90,615,000 m3) of balsam fir standing in 1931 were estimated to have died or been injured beyond recovery. Millions of cords of white spruce were also probably killed. Atwood noted increased difficulty of logging in affected stands as well as an increased risk of fire.Atwood, C.E. 1945. The status of the spruce budworm in Ontario and western Quebec. Entomol. Soc. Ont., 74th Ann. Rep.:52–54. Instead of affecting the whole area subject to budworm infestation, some past outbreaks have occurred in separate regions. For example, in the lower St. Lawrence and Gaspé regions, radial-growth studies of balsam fir and white spruce confirmed outbreaks known to have taken place in lower St. Lawrence in 1878 and 1912. The Gaspé area was thought to have escaped those outbreaks, but Blais found that the 1912 outbreak had covered more than 2 million ha in that region. Within affected regions, epidemics did not recur regularly. In 1965, Blais obtained further evidence from the radial growth on basal disks of balsam fir, white spruce, and
black spruce ''Picea mariana'', the black spruce, is a North American species of spruce tree in the pine family. It is widespread across Canada, found in all 10 provinces and all 3 territories. It is the official tree of the province of Newfoundland and Labra ...
(susceptible species), and non-susceptible white pine in the Laurentide Park, Quebec. He concluded that outbreaks occurred in 1704, 1748, 1808, 1834, 1910, and 1947. The more recent outbreaks seemed to be more severe than earlier ones, possibly due to an increase of highly susceptible balsam fir and a decrease of less susceptible white spruce following harvesting operations. Turner found evidence of a budworm attack in the
Lake Nipigon Lake Nipigon (; french: lac Nipigon; oj, Animbiigoo-zaaga'igan) is part of the Great Lakes drainage basin. It is the largest lake entirely within the boundaries of the Canadian province of Ontario. Etymology In the Jesuit Relations the lake is ...
region of Ontario occurring with the 1704 outbreak in Quebec's Laurentide Park. This was based on the pattern of radial growth in a single 300-year-old white spruce tree that showed a characteristic budworm suppression pattern beginning in 1702 and lasting for 10 years. Intensive searches failed to find other white spruces of similar age.


Interactions with humans


Pest of forests

The eastern spruce budworm ''Choristoneura fumiferana'' has been called “the most destructive forest insect in North America."Rose, A.H.; Lindquist, O.H. 1985
Insects of eastern spruces, fir and, hemlock, revised edition
Gov’t Can., Can. For. Serv., Ottawa, For. Tech. Rep. 23. 159 p. (cited in Coates et al. 1994, cited orig ed 1977)
Massive budworm epidemics erupt periodically in spruce–fir forests in northern and eastern Canada. Populations of spruce budworm vary in density over several orders of magnitude. Recorded densities in the boreal forest range from less than 0.01Miller, C.A.; Renault, T.R. 1976
Incidence of parasitoids attacking endemic spruce budworm (Lepidoptera: Tortricidae) populations in New Brunswick
Can. Entomol. 108:1045–1052.
to over 100 larvae per 45 cm branch tip. Damage to trees in forests can begin even before the
bud In botany, a bud is an undeveloped or embryonic shoot and normally occurs in the axil of a leaf or at the tip of a stem. Once formed, a bud may remain for some time in a dormant condition, or it may form a shoot immediately. Buds may be spec ...
s have flushed. Early instar larvae mine and kill these buds. Late instar larvae are voracious feeders, chewing off needles at their bases. In heavy infestations, old foliage is also eaten. Increment loss, tree deformity, and tree mortality follow several years of heavy infestation.Blais, J.R. 1980. Condition du sapin et de l’épineete blanche dans la région du parc des Laurentides en 1979 face à l’épidémic de al tordeuse et prévision des peretes. Can. ^^^, Laurentian For. Res. Centre, Ste.-Foy QC, Inf. Rep. LAU-X-43. 16 p.Brown, R.G. 1971. Spruce budworm in British Columbia. Can. Dep. Environ., Can. For. Serv., Victoria BC, For. Insect & Disease Survey, Pest Leaflet 31. 4 p. Defoliation of trees reduces their photosynthetic capacity and therefore curtails growth. In conifers, reduction in radial growth does not normally coincide with the first year of defoliation. For instance, the ring width of white spruce showed reduced growth throughout the stem beginning in the year after defoliation by the European spruce sawfly ('' Gilpinia hercyniae'' Htg.).Reeks, W.A.; Barter, G.W. 1951
Growth reduction and mortality of spruce caused by the European spruce sawfly ''Gilpinia hercyniae'' (Hymenoptera: Diprionidae)
For. Chron. 27(2):140–156.
One preliminary study showed that, during the first 3 or 4 years, repeated severe defoliation of white spruce by the spruce budworm was not reflected in reduced radial growth. However, in the
Lac Seul Lac Seul is a large, crescent shaped reservoir in Kenora District, northwestern Ontario, Canada. It is approximately long. It has a maximum (regulated) depth of 47.2 m, with a surface elevation of 357 m above sea level. Its level is raised in ...
infestation in northwestern Ontario, apparent radial growth suppression in white spruce first occurred in the 2nd and 3rd years of severe defoliation.


Control

Pest management of the eastern spruce budworm is often undertaken due to the incompatibility of budworm outbreaks with some human uses of the same forest. Management occurs through some manipulation of the environment, which is determined through cultural practice, or by the introduction of a regulatory agent such as a predator or an
insecticide Insecticides are substances used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed to ...
. In regard to massive outbreaks, the use of
insecticide Insecticides are substances used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed to ...
is a primary method of tree protection.


Pesticide

In New Brunswick, over 3,600,000 hectares were sprayed at least once between 1952 and 1967. Most of the sprayed forests were still “in good condition” in 1968. Although a scattering of dead trees occurred throughout the region, in no case did mortality destroy a major operating unit or disrupt a long-term management plan. In contrast, mortality exceeded 65% in 2 unsprayed check areas, each 155 km2. If the program of spraying against budworm had not been carried out, forest production in central New Brunswick is estimated to have been reduced to 20% of its normal production.


Biological control

Chemical controls are controversial because they only provide short-term protection and require multiple applications. As a result, research has been done on alternative biological controls using natural predators. A 1989 study found that woodland birds cannot effectively control the damage caused by budworms during outbreaks because their food requirements are exceeded. However, birds are important in controlling budworms and lessening damage caused by defoliation when budworm populations are less than outbreak levels. Inundated releases of ''
Trichogramma ''Trichogramma'' is a genus of minute polyphagous wasps that are endoparasitoids of insect eggs. ''Trichogramma'' is one of around 80 genera from the family Trichogrammatidae, with over 200 species worldwide.Consoli FL, Parra JRP, Zucchi RA (20 ...
minutum'' Ril., a species of parasitic wasp, have also been investigated for use as a biological control of ''Choristoneura fumiferana.'' Levels of egg parasitism were strongly affected by factors such as time of release, parasite density, and local weather. Some other factors that were less significant included the food supply of adult female parasites, elevation of the host egg-mass, host density, and the intensity of solar radiation. Temperature and host egg differences also influenced the biological characteristics of reared parasites, which could possibly affect the success of field releases. Due to the high degree of individual variation within each strain, rearing conditions were considered more important than the type of geographical strain of ''T. minutim'' utilized. The tree species on which the spruce budworm egg masses were laid did not influence the level of parasitism.


Pheromone traps

Pheromone traps may be used to watch ''C. fumiferana'' populations within forests in order to anticipate outbreaks. These traps release a synthesized pheromone that attracts male moths but previously used virgin females as a lure. This method of control has been utilized for over 20 years in some forests throughout Canada.


References


External links


Spruce Budworm in Maine, 1910–1976: Infestations and Control
{{Taxonbar, from=Q954655 Choristoneura Insects of the Arctic Moths described in 1865 Taxa named by James Brackenridge Clemens