Bug of the Day: Twospotted Spider Mite
The twospotted spider mite, Tetranychus urticae, is a total glutton. Infamous for eating just about everything – more than 200 species of ornamental, vegetable and fruit crops – the twospotted spider mite is the most economically important species of spider mite in Florida, and most anywhere else.
Associated most often with temperate zones and subtropical regions, the twospotted spider mite is found throughout the United States, and can overwinter in greenhouses in areas with cold climates. Oval in shape, the twospotted spider mite is about 1/50th of an inch long and under a microscope it looks a little bit like a flat, hairy potato that sprouted legs. They can be brown or orange-red, but are most often a green or greenish-yellow color.
Female twospotted spider mites lay their eggs on or under leaves and a single adult female can lay several hundred eggs in a lifetime. The mites produce fine silk webs to hold and protect their eggs, a trait that explains the “spider” portion of their name.
Twospotted spider mites damage plants by feeding, piercing the leaf tissue with their needle-like mouths and sucking the contents out of plant cells, one cell at a time. It’s estimated that one mite can destroy 18 to 22 cells per minute, and when that number is multiplied by hundreds or thousands of feeding mites, the accumulated damage can interfere with photosynthesis. This, in turn, causes affected leaves to turn gray or yellow and flowers to brown and wither. Ultimately, the plant may become completely defoliated and die.
What do twospotted spider mites like to eat? They’ll attack citrus, blackberry, blueberry, strawberry, tomato, squash, eggplant and cucumber. They also feed on ornamental plants including azalea, camellia, evergreens, holly, rose and viburnum. They are even pests to maple, elm, redbud and poplar trees. Because twospotted spider mites eat such a wide variety of plants, they are considered polyphagous (see this week’s Bug Word of the Day selection for a definition).
Fortunately, these mites do have natural enemies to keep their numbers in check. Spider mites are prey for ladybugs, minute pirate bugs, thrips, lacewing larvae and predatory mites. Five predatory mite species are commercially available to growers in the United States, and one, Phytoseiulus persimilis, is the most popular choice for controlling the twospotted spider mite. A single Phytoseiulus persimilis can consume 20 eggs or five adult spider mites every day.
Twospotted spider mites can be hard for home gardeners to detect and therefore, difficult to manage successfully.
The undersides of leaves should be examined with a magnifying glass, but the most efficient way to detect spider mites is to hold a sheet of blank white paper beneath the leaves, shake the branch or stem sharply, and let the mites fall onto the paper where they can be observed and identified. Infestations can sometimes be controlled with the use of insecticidal soaps or oils, and these options should be considered in lieu of pesticide whenever possible.
In 2011, the entire genome of the twospotted spider mite was sequenced. It was the first member of a major arthropod sub-group known as the chelicerates (which includes horseshoe crabs, sea spiders, spiders, scorpions and mites) to have its genome sequenced.
The twospotted spider mite is the only animal that can synthesize carotenoids, the yellow, orange and red pigments found in some vegetables. The mites probably obtained the genes that control carotenoid production from a fungus that originally lived symbiotically with the mite.
You can learn more about the twospotted spider mite at this “Featured Creatures” document from the UF/IFAS Entomology and Nematology Department.
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UF/IFAS Department of Entomology Photo by James Castner