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Current-year needles are preferred although older foliage may also be consumed during epidemics, especially when the host is balsam fir (Abies balsamea). At outbreak densities, feeding by the eastern blackheaded budworm on balsam fir results in mats of severed needles combined with silk and frass. These dry to produce a reddish appearance of fresh shoots on infested balsam fir in mid- to late summer. The symptoms are usually less intense on spruce, with some discoloration and deformation of fresh shoots. The damage is most pronounced on the distal portions of branches in the upper crown. As the damaged crown weathers, the crown becomes thinned or bare, especially in the upper half. Upper crowns that are completely defoliated may die and be evident as dead tops but this is not as common as it appears to be in infestations of the western blackheaded budworm (Acleris gloverana). High-density populations of the eastern blackheaded budworm have been contemporaneous with outbreaks of the spruce budworm, Choristoneura fumiferana, balsam woolly adelgid, Adelges piceae, and hemlock looper, Lambdina fiscellaria. Thus it has been difficult to characterize the damage caused by the eastern blackheaded budworm in the absence of these other insects (Miller, 1966).
Extensive outbreaks of the eastern blackheaded budworm in the late 1940s and late 1950s coincided with outbreaks of the spruce budworm. The extensive control measures undertaken for that insect probably impacted the blackheaded budworm. The only direct control programme for A. variana occurred in Newfoundland, Canada and involved comparison of aerial applications of two formulations of Bacillus thuringiensis (West and Carter, 1992). Poor results were attributed to the protected feeding sites occupied by the blackheaded budworm.
Severe defoliation occurs on mature balsam fir although there is one report of 100% defoliation of white spruce (Miller, 1966). The mortality and top-stripping of trees have been reported in only a few, isolated cases, usually where other defoliators were also active (Otvos, 1977). Miller (1966) commented that there is no marked reduction in radial increment of affected trees but no data are cited. Unlike A. gloverana, A. variana does not appear to cause significant damage to immature stands of host trees. When associated with other forest pests, damage by the eastern blackheaded budworm contributes to the overall decline in host tree vigour.