Twospotted spider mite, Tetranychus urticae
Order: Acari
Family: Tetranychidae
Description
Spider mites are small arachnids that are difficult to see without magnification. The twospotted spider mite is the most common spider mite infesting vegetables. Adult females are about 0.4 mm long and have four pairs of legs, no antennae, and a pair of red eyespots on the head. Their oval-shaped bodies range in color from green to yellow when active, or bright orange during dormant periods. Under magnification, two dark blotches are visible on either side of the adult’s body. Males have similar body shape and coloration as females but are smaller.
The eggs of twospotted spider mite are 0.14 mm long yellow or translucent balls. The larvae are about the size of eggs, have three pairs of legs, and are light yellow with rounded bodies. The coloration of nymphs varies from light yellow or green, to red or orange. The nymphs are smaller than adults but also have four pairs of legs and two dark spots on the body.
Many spider mite species produce webbing when their populations are high, which protects them from natural enemies and environmental fluctuations. Webs also help spider mites disperse to new hosts. The presence of webbing is a useful indicator for distinguishing spider mites from other vegetable pests such as aphids and thrips.
Two-spotted spider mite and eggs. Image credit: Bruce Watt, University of Maine, Bugwood.org
Pecan infested with twospotted spider mite. Note the presence of webbing. Image credit: Louis Tedders, USDA Agricultural Research Service, Bugwood.org.
Quick Facts
- Spider mites are small arachnids that are difficult to see without magnification. They are a common pest in yards and gardens. Symptoms of injury include flecking, discoloration (bronzing), and scorching of leaves. Injury can lead to leaf loss and even death.
- The twospotted spider mite is a common pest of many ornamental and vegetable plants.
- Feeding of twospotted spider mite causes stippling injury, discoloration, and scorching of leaves. Heavily infested plants may be stunted and die.
- Drought stress contributes to outbreaks of spider mites. Irrigation and moisture management can be an important cultural control.
- Natural enemies include small lady beetles, predatory mites, minute pirate bugs, big-eyed bugs, and predatory thrips. The release of predatory mites can be an effective management approach in greenhouses. Flare ups of spider can occur after applications of broad-spectrum insecticides which eliminate natural enemies.
- Under favorable environmental conditions, the twospotted spider mite can rapidly produce many generations which allows populations to develop resistance to pesticides.
Life history and habits
This species has four life stages: egg, larva, nymph, and adult. In areas with cold winters, the twospotted spider mite overwinters as adult females at the base of host plants, under debris, or in weeds in and around fields. As temperatures rise the following spring, activity resumes and the overwintered mites migrate to host plants to lay eggs on foliage. In controlled indoor environments, populations can remain active year-round. Unmated females can produce both male and female mites, which allows a single mite to establish a breeding infestation. A single female can lay around 100 eggs.
Colonies of the twospotted spider mite tend to reside on the undersides of leaves. When food becomes scarce, this species can migrate to new areas by crawling or using their web to disperse to new locations in a process known as ballooning. Often, the ballooning mites are composed of immature females that form a silk ball. The twospotted spider mite can survive a wide range of temperatures from 10-40°C (50-104°F). Dry conditions favor spider mites, and the entire life cycle is completed in 10 days or fewer under hot, dry conditions. The twospotted spider mite can attack many ornamental and vegetable plants. Some vegetable hosts include tomato, corn, eggplant, bean, pepper, and cucurbits.
Two-spotted spider mite. Image credit: Frank Peairs, Colorado State University, Bugwood.org.
Two-spotted spider mite injury and webbing on indoor-grown medical marijuana. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org.
Injury
Spider mites feed by puncturing plant cells with their piercing-sucking mouthparts and removing contents of the cells, which depletes them of chlorophyll. This reduces photosynthetic output and overall plant productivity. Feeding produces stippling injury on the upper leaf surface, which appear as white, grey, or yellow pinpoint dots. The foliage of heavily infested plants can turn yellow and eventually drop prematurely. Silken webbing can be abundant on severely infested plants. When left untreated, spider mites frequently kill or cause serious stress to plants.
Two-spotted spider mite stifling injury to bean leaves. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Bell pepper infested with twospotted spider mite. Image credit: O. P. Sharma, Bugwood.org.
Peanut field with severe feeding injury due to twospotted spider mite feeding. Image credit: John C. French Sr., Retired, Universities: Auburn, Georgia, Clemson, and Missouri, Bugwood.org.
Monitoring
Plants can be inspected for feeding injuries, mites, and webbing. The undersides of leaves can be examined for mites each week with a 10x hand lens. Spot spraying can be effective when localized or spotty mite populations are detected within a field. When spot spraying, a buffer zone of at least 100 feet should be treated beyond the infested area.
Cultural control
Cultural controls for spider mites involve reducing plant stress—particularly drought. Adequate watering of plants during dry conditions can limit drought stress and prevent spider mite outbreaks. In greenhouse or indoor settings, higher humidity can decrease spider mite populations. Periodic hosing of plants with a forceful jet of water can physically remove and kill many mites, as well as remove the dust that collects on foliage and interferes with mite predators. Rinsing plants mid-season can hinder population booms but is less effective on heavily infested plants. Removing weeds in grassy areas around fields and greenhouses can prevent the buildup of mite populations. However, mowing is not recommended in weedy areas that already contain mites to prevent the pest from migrating to nearby plant hosts.
Biological control
There are various insects and predatory mites that provide natural control of the twospotted spider mite. These include spider mite destroyers, Stethorus spp. (Coleoptera: Coccinellidae), minute pirate bugs, Orius spp. (Hemiptera: Anthocoridae), big-eyed bugs, Geocoris spp. (Hemiptera: Geocoridae), predatory thrips (Thysanura: Aelothripidae, Thripidae), and predatory mites (Acari: Phytoseiidae). Certain predatory mites are naturally occurring, while others are commercially available for release as biological controls in greenhouses or other indoor areas. It should be noted that predatory mites require high humidity, and their release is not effective for outdoor control of twospotted spider mite in Colorado.
Chemical control
Chemical control usually involves pesticides specifically developed for spider mite control (miticides or acaricides). However, multiple applications every 10 to 14 days are necessary since the pesticides do not kill eggs. Repeated applications can be costly, promote resistance in the pest population, and have negative effects on natural enemies. Examples of insecticides for spider mite control in Colorado include acephate, abamectin, bifenthrin, horticultural oils, insecticidal soaps, and sulfur. Pesticides with different modes of action can be rotated to prevent resistance, and the use of broad-spectrum pesticides should be avoided when possible.
Spider mite destroyer (Stethorus punctum picipes) Image creidt: F.C. Schweissing, Bugwood.org
CSU Extension Fact Sheet
Download or view the CSU Extension’s PDF fact sheet for your reference.
References
Bolda, m., L. Bettiga, E. Show, E. Perry, and H. Thomas. 2015. Available here.
Hodgson, E., and A. Dean. 2022. Twospotted Spider Mites. Iowa State University – Extension and Outreach. Available here.
Muza, A. 2021. Two-Spotted Spider Mite on Vegetables. Penn State University – Extension. Available here.
Shu-Jen, T. 2016. Survival and Reproductive Strategies in Two-Spotted Spider Mites: Demographic Analysis of Arrhenotokous Parthenogenesis of Tetranychus urticae (Acari: Tetranychidae). Journal of Economic Entomology. 109(2): 502-509.
UC IPM. (n.d.). Twospotted Spider Mite. University of California – Department of Agriculture and Natural Resources. Available here.
Xiao et al. 2011. Evaluation of corn plant as potential banker plant for supporting predatory gall midge, Feltiella acarisuga (Diptera: Cecidomyiidae) against Tetranychus urticae (Acari: Tetranychidae) in greenhouse vegetable production. Crop Protection. 30(12): 1635-1642.
Young-Lak, P., and L. Joon-Ho. 2002. Leaf Cell and Tissue Damage of Cucumber Caused by Twospotted Spider Mite (Acari: Tetranychidae). Journal of Economic Entomology. 95(5): 952-957.