Eriophyid Mites By Dr. Raymond Cloyd, Associate Professor Department of Natural Resources and Environmental Sciences University of Illinois This month I received a sample of coneflower, Echinacea spp. that was "heavily" infested with eriophyid mites……I mean over 500 mites per flower head (I have to admit I was in entomological heaven!!). The mites were primarily concentrated in the flower heads where they were causing distorted flower growth. In fact, the flowers were not marketable. It is interesting to note that the mites were only present on the coneflowers, regardless of cultivar, despite an assortment of other perennials surrounding the crop. Eriophyid mites are extremely tiny (less than 0.3 mm in length), microscopic 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 remainder of the body (Idiosoma). The idisoma is similar to the abdomen of insects. Eriophyid mites only have 2 pairs of legs, which is a unique characteristic among mites (all other mites have 4 pairs of legs). They cannot be detected with the unaided eye. These mites are a specialized group of plant feeders. In general, many eriophyid mites feed on a few closely related species or genera of plants. At the tip of the idisoma is a sucker, which allows the mite to hold on to the plant surface. Eriophyid mites feed deep within the plant tissues sucking out plant juices with their stylet-like mouthparts and transferring a substance, which causes deformation of plant growth. Feeding generally results in densely packed or distorted growth to both the flowers and foliage that appears "rough" looking. 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 are also the only group of mites known to transmit plant viruses. Eriophyid mites tend to live together in large numbers 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. Eggs are spherical and generally laid in groups. They hatch in less than two weeks into young mites that may take approximately two weeks to a month to mature into adults. The reproductive potential of eriophyid mites is very similar to two spotted spider mite. Each female mite may lay up to 100 eggs. Several generations may occur throughout the growing season. Eriophyid mites attack a variety of greenhouse-grown crops including carnation, chrysanthemum, delphinium, hibiscus, and some ornamental cacti. More recently they have been discovered feeding on poinsettia. They feed on all plant parts including buds, flowers, leaves, and twigs. Eriophyid mites can easily come in on plant material from a supplier. Suppliers may not know they have eriophyid mites unless damage is noticed. Once damage is evident, it is too late because the mites are already established within the plant. As a result, preventative spray applications of pest control materials are needed to prevent damage from occurring. However, the number of effective pest control materials for controlling eriophyid mites is limited, and efficacy data is minimal. Pest control materials with translaminar properties are your best choices for "managing" eriophyid mites. These would include abamectin (Avid) and chlorfenapyr (Pylon). Additional pest control materials that may be "active" on eriophyids are pyridaben (Sanmite), fenpyroximate (Akari), and endosulfan (Thiodan). Several of these products may be harmful to beneficial insects and mites, in particular ­endosulfan (Thiodan). An important management strategy even if applying pest control materials is to dispose of plants/plant parts that are showing symptoms. In addition, it is generally advisable to dispose of plants surrounding the infected plants; they may also be infested ­but symptoms are not evident. In addition, it is beneficial to send suspected plants to a university diagnostic clinic for verification. Controlling eriophyid mites for the next season generally involves applying pest control materials prophylactically that is before damage is noticeable, because once plants show visible symptoms ­it is too late!! 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 currently available for use in commercial greenhouse production systems.