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Spider mites - know your enemy

spider mites, pest red spider mites, red spot spider mites
Spider mites are common pests in the urban landscape. They can inflict serious damage to trees, shrubs and flowers. Both evergreen and deciduous plants may be attacked. Spider mites are not insects but are more closely related to ticks and spiders.

They have four pairs of legs, no antennae and a single, oval body region. Their common name is derived from their ability to produce silk, which most species spin on host plants. Mites are tiny—about the size of the period at the end of this sentence. They can also be very prolific, which is why infestations often go unnoticed until plants exhibit significant damage.

Many species of spider mites can be found in landscapes. The twospotted spider mite, Tetranychus urticae (Koch), and spruce spider mite, Oligonychus ununguis (Jacobi), are the most common pests. Other species with fewer host plants include: European red mite, Panonychus ulmi (Koch), found on apple trees; honeylocust spider mite, Platytetranychus multidigitali (Ewing); southern red mite, Oligonychus ilicis (McGregor), on a variety of plants; boxwood spider mite, Eurytetranychus buxi (Garman); and the
oak mite, Oligonychus bicolor (Banks).

Types of Damage
Spider mites have needle-like mouthparts and feed by piercing the leaves of host plants to suck out the fluids from individual plant cells. This causes the leaves to appear stippled or flecked, with pale dots where the cellular contents have been removed.

Prolonged, heavy infestations cause yellowing or bronzing of the foliage and premature leaf drop similar to drought stress. Severely-infested plants may be stunted or even killed. Most of the mites feed from the undersides of leaves, although the damage is most evident from the upper surface.

Heavily infested plants may be discolored, stunted or even killed. Web producing spider mites may coat the foliage with fine silk which collects dust and looks dirty. They are even known to wander inside when numbers are abundant and walk about on counters and offices furniture. They frequently enter computer equipment and
appliances, apparently for the warmth. Some of these invasions may originate on populations from nearby house plants.

Life Cycles and Habits
Spider mite species seem to be active in either warm or cool weather. The twospotted, European red, honeylocust, and oak spider mites do best in dry, hot summer weather. The spruce and southern red spider mites do best in cool spring and fall weather.

All spider mites go through the same stages of development, which is similar but not exactly the same as in insects. Adult females usually lay eggs on their host plants.

The eggs hatch in days to weeks into the first stage, called a larva. Larvae are round bodied and have only three pairs of legs. The larvae feed for a few days, seek a sheltered spot to rest and then molt into the first nymphal stage. The first nymphal stage has four pairs of legs. The first nymphs feed a few days, rest and then molt into the second nymphal stage. These nymphs feed, rest and molt into the adult stage. Adult males are usually the size of the second ny mph and have pointed abdomens. The females have rounded abdomens and are the largest mites.

Most spider mites spend the winter in the egg stage but the twospotted spider mite overwinters in protected places as resting adult females.

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