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Description
The two spotted spider mite is quite small (< 1/60 in.),
oval-shaped, has 4 pieces, 7 legs, and is yellowish or greenish
with two dark spots on its back which are composed of food
contents. Males are slightly smaller (1/80th in.) and slimmer
than females with a pointed abdomen. The eggs of the two-spotted
spider mite are pearly white, circular, and on the webbing
on the foliage. Young mites resemble the adults except in
size and possess only 3 pairs of legs in the first stage.
Later they develop a fourth pair of 7 legs. The immature mites
pass through three stages before becoming adults.
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Click
on image for larger version
Figure
1. Spider Mite Damage on a Cherry Leaf
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Life
Cycle
Spider mites attack many species of plants including common greenhouse
crops such as tomatoes, carnations, chrysanthemums, snapdragons,
violets, roses, and fuchsia. Spider mites may be found on any part
of the plant, but most often are on the middle-aged leaves. Under
severe infestations, they may be found on the growing tips. Generally,
the lower leaf surface is preferred over the upper surface. Egg
laying and development is affected by temperature. The optimum temperature
for egg laying is 30 degrees C with an individual female laying
100 eggs and living for 30 days. Under these conditions, a new generation
is produced every eight days. Under low temperatures (21 degrees
C) development may be slowed taking 14 days for a generation and
at 12 degrees C the process may extend to 40 days. Under optimum
conditions, a female mite may produce 13 million offspring during
her lifetime. Spider mites are most damaging under greenhouse conditions
of high temperature and low humidity.
Damage
Damage caused by the two-spotted spider mite will vary according
to the infestation level however, mites feed by piercing plant cells
with their mouthparts and sucking out the cell contents. Lightly
infested plants will have foliage with pale blotches or spots showing
through the leaf while with heavy infestations the entire leaf appears
light in color, dries up, and often turns a reddish-brown with blotches
in and around the edges. Plants generally lose their vigor and die.
Silken threads will also be present among the foliage. The mites
will be located on the underside of the foliage and appear as tiny,
reddish, greenish, yellowish, or blackish, moving dots. The mites'
color appear to be related to the type of host plant.
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Click
on image for larger version
Figure
2. Two-Spotted Spider Mite Adults, Nymphs, and Eggs
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Nonchemical
Control
Heavily
infested plants should be kept separate from the production
area or discarded. Predatory mites are also commercially available.
Chemical
Control
Applications of commercial miticides, horticultural oils,
and insecticidal soaps may also be used when infestations
are severe.
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Authors:
Susan T. Ratcliffe (sratclif@uiuc.edu)
Michael E. Gray (m-gray4@uiuc.edu)
Kevin L. Steffey (ksteffey@uiuc.edu)
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