Eriophyid Mites | |
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| June 16, 2004 | |
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Eriophyid mites, also known as blister, bud, gall, and rust mites, are extremely tiny (less than 0.3 mm long), worm- or spindle-shaped mites with elongated bodies. They resemble cigars, with the head and legs located on one end of the body. They have two body regions: mouthparts (gnathosoma) and the rest of the body (idiosoma). The idisoma is similar to the abdomen of insects. Eriophyid mites possess only two pairs of legs, which is a unique characteristic among mites (all other mites have four pairs of legs as adults). They cannot be seen without some type of magnification (that is, 10X hand lens or dissecting microscope). These mites are a specialized group of plant feeders. Many eriophyid mites, in general, feed on a few closely related species or genera of plants. At the tip of the idisoma is an attachment that allows the mite to hold on to the plant surface. Eriophyid mites feed deep within the plant tissues (meristematic region), sucking out plant juices with their styletlike mouthparts and transferring a substance or toxin, which causes deformation of plant growth. Feeding typically results in densely packed or distorted growth that appears “rough.” However, eriophyid mite feeding can result in a variety of symptoms, including galling, clustering or “witches’-broom,” swollen or thickened growth, leaf blistering, and russetting or bronzing of leaves. Eriophyid mites may be categorized based on the type of injury they cause to plants, with the two primary classifications being (1) those that create galls (gall-formers) and (2) those that stunt new plant growth. Additionally, eriophyid mites are the only group of mites known to transmit plant viruses. Eriophyid mites tend to live together in large clusters and reproduce within the folds of plant tissues. With the aid of a dissecting microscope (set at 100X), the mites and eggs can be seen. The eggs are spherical and generally laid in groups, although they can be laid individually. They hatch in less than 2 weeks into young mites that may take about 2 weeks to a month to mature into adults. The reproductive potential of eriophyid mites is very similar to twospotted spider mite, Tetranychus urticae. Each eriophyid female mite may lay up to 100 eggs. Several generations may occur throughout the growing season. Eriophyid mites attack a wide range of ornamental plants, including maples (Acer spp.), ash (Fraxinus spp.), walnut (Juglans spp.), cherry (Prunus spp.), and elm (Ulmus spp.). The primary eriophyid mites that attack plants belong in the genus Eriophyes spp. Table 1 lists numerous gall types caused by eriophyid mites on trees and shrubs throughout the United States. Eriophyid mites feed on all plant parts, including buds, flowers, leaves, and twigs. Table 1. Gall types caused by eriophyid mites on ornamental trees and shrubs in the United States. Gall type/ Casual organism/ Host Insects can actively transport eriophyid mites from one location to another. For example, Eriophyces ribis rears up and sways in the air and then attaches itself to an aphid, ladybird beetle, or other insect it comes into contact with. Because they are difficult to detect, they can be easily moved around. In fact, a new eriophyid mite, Calacarus carnitus, also known as the purple or ribbed tea mite was recently reported in Florida. It is a distinctive purple color with a white, waxy residue. The mite has also been reported in Georgia and California. Photos of plant injury can be found at http://www.mrec.ifas.ufl.edu/lso/erio-mite/erio-mite.htm. Once injury is evident, it is too late because the mites are already established within the plant. As a result, preventive spray applications of miticides are needed to prevent injury from occurring. However, the number of effective miticides for controlling eriophyid mites is limited. Two insecticides/miticides that may be effective include abamectin (Avid) and bifenthrin (Talstar), but these materials generally need to be applied before eriophyid mites enter the terminal growth and cause injury. An important management strategy even if applying miticides is to dispose of plants showing symptoms. In addition, it is generally advisable to dispose of plants surrounding the infected ones because they may also be infested. Also, it is beneficial to send suspected plants to a university diagnostic clinic for verification. Biological control of eriophyid mites is very difficult because they live and feed in buds or galls, which protects them from large predators. In addition, there are no effective natural enemies for eriophyid mites. | |
| Author: | Raymond A. Cloyd |
