Mites can be a very destructive pest in orchid collections. Mites are minute arthropods with four pair of legs. They are closely related to ticks, spiders, and scorpions. They are not true spiders, but some species spin fine webs to protect themselves and their eggs.They get the 'spider' part of their common name from webbing. They belong to the genus Tetranychus. The most common in orchid collection is Tetranychus urticae, of which one form is bright red, and others are yellowish or greenish; hence, the common name of red-spider. The mite's body contents (large dark spots) which are often visible through the transparent body wall , give the better known name of two-spotted spider mites.
Mites can multiply quickly during be out of contol before you even notice them. When searching for spider mites, their fine webbing will likely be noticed first. Look on the undersides of leaves and between leaves for the webbing. These eight-legged pests are so tiny (about 1/50th of an inch), they are difficult to see with the unaided eye. For visual detection of the mites, a magnifying lens , or pocket microscope will be a big help. The presence of mites can be also be determined by rubbing a white cloth over the suspected infestation. If mites or eggs are present, reddish brown stain will be seen on the cloth. Another technique is to tap on a leaf over a sheet of white paper, then you may be able to see little moving specks on the paper.
The spider mites and false spider mites are plant feeders. All mites have needle-like piercing-sucking mouthparts. They damage the leaves and pseudobulbs of orchids, by penetrating the plant tissue and suck the plant juice out. They are particularly troublesome on thin leaved orchids, such as members of the Oncidium Alliance, Cymbidium, and Cycnoches. However, they attack all orchids. They leave tiny white scars on the undersurface of the leaves, where they prefer to live. The result is a fine silver stippling of the leaf surface and the psuedobulbs.
They are also injurious to the flowers. Their favorite point of attack on flowers is along the seams where the sepals come together in the bud, where they leave small transparent spots surrounding the punctured areas. One such spot is a blemish, but many spots actually ruin the flower. Sometimes as the sepals split apart, the mites enter the bud and cause enough damage to distort the flower.
Hot, dry conditions are often associated with population build-up of spider mites, but infestations can occur anytime during the year. Under optimum conditions (70-80°F/21-27°C), most mites hatch in as little as 3 days, and become sexually mature in as little as 5 days. The females can lay upwards of 20 eggs a day, for a producing life of 2 to 4 weeks. The warm, dry conditions of greenhouses allows mite populations to survive, so infestations can occur even in winter.
These viciously destructive mites are also very small, similarily requiring a magnifying lens, to detect them. They are different from the spider mites as they do not spin webs. They also feed on top and bottom surfaces of the orchid leaves. They produce pits of dead tissue, which if the infestation is extensive, can cause the death of the leaf. The most often countered species are Brevipalpus californicus, and Tenuipalpus pacificus (the Phalaenopsis mite). All damage a number of orchids. Control is same as Spider Mites above.