Galls
Galls are outgrowths in plant
tissue in response to insect and
mite infestations or disease
infection.
Galls are plant tissue that
provides shelter and nutrition
for the inhabiting organism.
The hackberry nipple gall is caused by a
psyllid (Pachypsylla celtidismamma) insect.
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Galls
There are numerous types of galls
that form on oaks caused by wasps.
Wool sower gall on oak is caused by a
wasp (Callirhytis seminator).
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Roly-poly gall on oak is caused by a
wasp (Andricus sp.).
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Galls
Roly-poly gall cut in half
showing the wasp larvae in
the center of the gall.
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Galls
The horned oak gall wasp
(Callirhytis cornigera)
produces a large woody gall
on the stems of pin oak
(Quercus palustris).
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Galls
The mossyrose gall is
caused by the wasp
(Diplolepsis rosae).
It forms thread-like
masses of growth that
form around the stem
of roses.
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Galls
The witchhazel gall is a conical gall
induced by a single aphid (Hormaphis
hamamelidis) in the spring. The aphid
reproduces filling the gall with many
offspring that leave the gall in
summer to feed on birch.
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Galls
Galls can also be caused by Eriophid mites.
The elm spindle gall is caused by
the mite (Eriophyes parulmi).
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The maple bladder gall is caused by
the mite (Vasates quadripedes).
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Galls
The ash flowergall mite (Eriophyes
fraxiniflora) infests the male
flowers of ash (Fraxinus).
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Galls
Galls can also be induced by disease organisms. Cedar-apple rust is caused
by the fungus Gymnosporangium juniperi-virginianae. This rust causes a
gall on cedar trees where it overwinters. In the spring, gelatinous strands
exude from the gall to spread spores.
Rust gall on red cedar
(Juniperus virginiana).
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Galls
Crown gall is caused by a bacterium
(Agrobacterium tumifaciens).
It induces the plant to form
irregularly-shaped woody galls.
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Galls
Although similar looking
to Crown gall, this gall on
Forsythia is caused by
the fungus Phomopsis.
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