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DEPARTMENT OFPRIMARY INDUSTRY AND FISHERIESFactsheetENT-429 September 2008Biology and Pest Management of Spider MitesLanni Zhang, Entomology, Plant IndustriesBACKGROUND Mites are microscopic arthropods that are classified in the order Acarina. Theyare not insects but are related to ticks and spiders.There are over 40,000 described species of mitesin the world. Some of them live freely in soil or water; some are found on plants and some are associatedwith other animals. Due to their small size most of them are difficult to see with the naked eye.Mites that are plant pestsinclude spider mites(family Tetranychidae), false spider mites(family Tenuipalpidae), tarsonemid mites(family Tarsonemidae) and the rust or gall mites(family Eriophyidae).These mites cause damage by piercingplant cells and suckingout their contents. In heavy infestations mites may even kill the host plant.Two spotted mite adult and eggOriental red mite adult and eggSpider mites are given their name as they often spin characteristic protective silk webs. This family has more than 1000 species, which include some species of quarantine importance, and many species that maycause heavy losses to major food crops and ornamental plants. These include the infamous two-spottedmitesTetranychus urticae, and other major economic spider mite pests, which have been recorded in the Northern Territory e.g. oriental red mite, Eutetranychus orientalis-primarily a pest of citrus;vegetable spider mite, Tetranychus neocaledonicus;and avocado brown mite, Oligonychus punicae. These speciesattack a wide rangeof horticultural crops. Mites may cause serious damage to plants but since they are microscopic they are usually not noticed until damage symptoms appear on the plant.APPEARANCESpider mites are very tiny; the adult females are only 0.3-0.5 mm long and the males are even smaller. They are often red, brown, green or yellow in color and they can be seen clearly with the aid of a lens. The immature stages resemble the adults except in sizeand they have three pairs oflegs at larval stage and four pairs oflegs at pre-mature and adult stage. Two-spotted mite females are oval in shape and yellowish to greenish in colour and havetwo dark spots ontheirshoulders. Their eggs are translucent,about 0.1 mm in diameter,pale yellow or green in colour and have distinctive red eye spots before hatching. Oriental red mite females are ovoid and brown-green to dark green with light coloured legs. The smaller male mite has legs up to three times the length of the body.
© Northern Territory Government, 2010Page 2of 3LIFE CYCLE AND BIOLOGYThere are five stages in the life cycle of spider mites: egg, larva, protonymph, deutonymph and adult. Most species of spider mites prefer to colonize and lay eggs on the underside of leaves, suchas the two spotted mite,but some spider mites, such as the oriental red mites, are often found on the upper side oftheleaf. The eggs of spider mitesare deposited singly, directly on the host leaf surfaces. Female adults can lay more than 100 eggs during their 30 day life cycle. Development from egg to adult takes about one week in the tropics,so there may be many overlapping generations in a single season. Their populations can increase rapidly and cause extensive plant damage in a very short time when conditions (temperature, humidity and food)are suitable. Two-spotted mites have been recorded on more than 900 species of knownhosts, including more than 150 hosts of some economic value,which includes most of the important agricultural crops and ornamental plants. In the Darwin area, two-spotted mite is one of the most serious pests in the dry season. Two-spotted mites have been recorded on vegetables such as snake beans, eggplant, cucurbits such as watermelon, fruit trees such as carambola and pawpawand ornamentals such as palms, heliconia, gerberas as well as many other native and horticultural plants.SYMPTOMS AND DAMAGE Spider mites have needle-like mouthparts and feed by piercing the leaves of host plants and sucking out the fluids from plantcells. Feeding causes yellow spots on the leaves and in heavy infestations, foliage hasa yellowing or bronzing appearanceand may suffer from premature leaf drop. In situations where there is severe damage this may lead to plantdeath.Mites prefer the young leaves, however inheavy infestations, the older leaves are also affectedand sometimes webbing may be seen all over the plant. Oriental red mite, Eutetranychus orientalis,is primarily a pest of Citrus,however, the mite has several alternative host species such as cotton, squash, frangipani and grapevines. Oriental red mite damage is similar to that caused by two-spotted mite, infested leaves have a chlorotic appearance and may become weak and finally drop. Spider mite damage to watermelon leafOriental red mite damage to Kaffir lime leavesSpider mite damage to taro leafSpider mites and webbing on bean plant