Two spotted spider mite (Tetranychus urticae) are a pest commonly found on a wide variety of greenhouse crops, while the carmine spider mite (Tetranychus cinnabarinus) is most commonly found in tomatoes. Spider mite populations can grow very rapidly under ideal conditions, namely hot and dry. Spider mites have the capacity to cover plants in webs, and if populations get large enough, entire plants can be destroyed.
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Spider mites go through 5 life stages, egg, larva, protonymph, deutonymph and adult. Between each stage of development the spider mite goes into a quiescent stage where it does not feed or move, but stays still with its legs curled under. All stages, except egg, are mobile, feeding and can be found on the crop. In any given population there are generally 3 times more females than males. One female spider mite can deposit up to 40 eggs over 10 days. If the female is unfertilized all of the eggs laid will be male. Symptoms and Signs: Spider mites cause damage by feeding on the plant tissue. Each feeding leaves a small yellow dot on the leaf, and when there are many feeding sites, the leaf has a yellow speckling pattern. Generally, damage is found at the base of the leaf and along the veins, as these areas provide the most cover for the mites. When populations of spider mite are high enough webbing can be seen on the leaf, most often near the stem. If left untreated, leaves and even the plant will turn brown and die.