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Description
Mites differ from insects in that they have 8 legs and 2 body
regions whereas insects have 6 legs and 3 body regions. There
is one exception however, young mites or nymphs have only
6 legs in their early stages and gain the 4th pair of legs
as they mature. Mites also vary greatly in color as their
appearance is a function of the host plant on which they are
feeding. Most of the coloration of spider mites results from
the accumulation of food material and waste in the body. Consequently,
coloration is more pronounced just prior to molting in nymphs
and in more mature adults.
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Figure 1. Leaf Blister Mite Damage on Pear
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The
spruce mite is quite small (1/60 inch) and usually a dark reddish
color. In some cases, the mite may be dark green. The legs and front
part of the body are buff or tan colored. Large quantities of "spider-like"
webbing are usually produced during feeding the process. European
red mites are bright to brownish-red and unspotted. The body is
quite elliptical in outline and about 1/75 inch in length. There
are four rows of long curved spines down the back, each borne on
a whitish tubercle. The two-spotted spider mite is about 1/60 inch
long and ranging in color from pale yellow through green to brown
to orange. The male is smaller with a narrower body and pointed
abdomen. Two dark spots, composed of food contents, show through
the transparent body wall. The mites are oval in shape and sparsely
covered with spines.
Life
History
Most mites have a similar life cycle however, certain species overwinter
either as eggs or adults. The spruce and European red mites overwinter
as eggs while the honeylocust spider mite overwinters as a mature
female. The overwintering sites vary (ie. spruce mites and two-spotted
spider mites on the foliage, honeylocust spider mites in bark cracks
and crevices of the host plant and European red mites on twigs and
smaller branches). Once mites hatch from the egg, they begin feeding
on the foliage rupturing the cells and withdrawing the contents.
The result is the presence of tiny chlorotic flecks and a bronzing
of the foliage. Extensive feeding will result in stippling, and
a yellow and white cast to the leaves.
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on image for larger version
Figure 2. European Red Mite Damage on Apple
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Mites
are very prolific and populations can build up quite rapidly.
Most mites are active throughout the growing season, however
the spruce spider mite is a cool season mite and is more prolific
in late spring/early summer and late summer/early fall. During
hot dry weather, they tend to hibernate. However, the damage
caused by their feeding usually coincides with the first hot
dry spells of summer.
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Damage
Damage from mite infestations can be quite pronounced and significantly
reduce the vigor and growth of affected plants. Webs are usually
present as well as a graying of the foliage particularly on evergreens.
Close examination of the needles and webs reveals tiny flecks or
particles which are usually the mites themselves. Holding a light
sheet of paper under a branch and shaking the branch vigorously
will dislodge them and facilitate a correct diagnosis.
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