Choristoneura fumiferana

Choristoneura fumiferana, the eastern spruce budworm, is a species of moth of the family Tortricidae. It is also commonly referred to as the spruce budworm. It is one of the most destructive native insects in the northern spruce and fir forests of the eastern United States and Canada. Its range is also the widest of all the budworm species. Eastern spruce budworm populations can experience significant oscillations. During outbreaks, populations grow to extremely high densities, compared to the relatively low levels that occur in between. These outbreaks are highly destructive and can cause both economic and ecological damage. As a result, methods of control are utilized. Several theories exist regarding these cyclical outbreaks: association with balsam fir maturation, catastrophe theory, dispersal from an epicenter, and oscillations synchronized by entrainment. The first recorded outbreak of the spruce budworm in the United States occurred in Maine in about 1807. Another outbreak followed in 1878. Since 1909 there have been waves of budworm outbreaks 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. In 20th-century eastern Canada, the major outbreaks occurred in periods circa 1910–20, c. 1940–50, and c. 1970–80. These outbreaks impacted, respectively, 10, 25, and 57 million hectares of forest. Longer-term tree-ring studies suggest that spruce budworm outbreaks have been recurring approximately every three decades since the 16th century. Paleoecological studies suggest the spruce budworm has been breaking out in eastern North America for thousands of years. The spruce budworm disperse locally after hatching and practice more long-range migration as adults to avoid harsh weather conditions. While moving through the life cycle stages of egg, caterpillar, pupa, and adult, this species risks attack from predators including birds and spiders as well as numerous parasitoids. During mating, females release sex pheromones to attract males. After a mate has been successfully attracted, the males deliver a nuptial gift to the female during copulation. Clemens originally named the eastern spruce budworm, C. fumiferana, in 1865, which was recognized as a Nearctic representative of the genus Choristoneura. At this time, the name applied to populations in a variety of geographic regions and biotopes. 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' 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 along the edge of the Laurentian Shield to the Mackenzie River area near the Arctic Ocean. 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 forest region, with alpine fir and interior spruce as hosts. Budworm populations from Rocky Mountain regions south of the area of introgressive hybridization of spruce differ from C. biennis. Other budworms are of little or no consequence with respect to spruces. 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 as well as the Great Lakes-St. Lawrence, Northern, and Acadian forest regions. This range extends westward to Alaska. The spruce budworm is commonly found in boreal and sub-boreal forest regions, specifically those that consist of spruce-fir forests. The main hosts of the eastern spruce budworm in eastern North America are balsam fir, white spruce, and black spruce, 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. Traditionally, the eastern spruce budworm prefers balsam fir over white spruce. 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. 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. 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 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.