Galls
> Eastern Spruce Adelgid
Pest: Eastern Spruce Gall Adelgid (Adelges abietis
(Linnaeus))
Order: Homoptera
Family: Adelgidae
Host Plants:
Primarily Norway spruce (Picea abies) and White spruce (P.
glauca ), others
Description:
The Eastern spruce gall adelgid causes galls to form at the
base of the new shoots, in the spring. These galls will be about
3/4" in total length and be pineapple-shaped. By autumn, these
galls are brown and the shoot growth beyond them is dead. In heavy
infestations, or after years of repeated infestation, the host tree
will have the appearance of dying from the perimeter inward. Extended
infestations can greatly weaken the host to a point where secondary
attackers (insects and diseases) can then successfully colonize
and perhaps even kill the host. In Christmas tree plantations, this
pest can render trees unfit for sale. Another gall, that is sometimes
found on the same host plants as the Eastern spruce gall adelgid,
is caused by a midge (a small type of fly). This midge gall (Mayetiola
piceae Felt) is usually of little importance.
Life Cycle:
Over-wintering immature females can be found at the base of
the buds on the host plant. In the early spring, they resume development
and produce eggs about the time of budbreak. These eggs hatch in
about ten days and the immatures begin to feed on the new needles.
This feeding stimulates gall formation, which surrounds the nymphs.
New galls will almost appear to be normal green growth but only
close inspection, at this time will reveal the abnormality. By late
August, these galls will dry, crack open and the immature adelgids
will emerge and mature into winged, egg-laying females. The eggs,
usually found on the needles, will hatch in late summer and the
nymphs will settle down at the base of the new buds on healthy shoots.
Management Strategies:
Galls dry and open between 2000 and 3000 GDD which is approximately
late August into October, in Massachusetts.. Mostly, this occurs
closer to the beginning end of this specific GDD spectrum. Applications
of horticultural oil sprays are extremely effective in managing
this pest prior to gall formation. They can be administered either
in the late summer or in the early spring before budbreak and whenever
the correct weather conditions prevail. Once galls have started
to form there is virtually no management strategy. Pruning or shearing
of the branches, at a level that removes the galls, usually requires
the removal of too much foliage.
Images:
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Exposed, over-wintering nymphs of the Eastern spruce gall
adelgid that are settled at the base of buds (UMass Entomology
teaching collection).
A newly forming gall of the Eastern spruce gall adelgid at
the base of a new shoot, in the spring. (R. Childs)
Old, dried galls of the Eastern spruce gall adelgid. Note
how the entire shoot growth was killed by this pest. (R. Childs)
Immatures of the Eastern spruce gall adelgid that have emerged
from the gall and are now settled on the stem for the fall
and winter. (R. Childs)
A smaller gall, of little significance, that is caused by
a midge (fly) and which is commonly also found on some of
the same host plants as the Eastern spruce gall adelgid. (R.
Childs)
Many dead tips on a spruce tree that were caused by the attack
of the Eastern spruce gall adelgid over the course of several
years. (R. Childs).
A gall of the Eastern spruce gall adelgid that has been cut
open to reveal the chambers and immature adelgids within.
Lengthwise, this gall is about 3/4". Note that many tiny adelgids
occupy each chamber. (UMass Entomology teaching collection).
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Galls
index:
Cooley Spruce Gall Adelgid
Eastern Spruce Adelgid
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