Introduction

The Tetranychidae family is commonly known as spider mites as some species spin dense, silken webbing to help protect the colony from predators (although many only use silk to protect their eggs). They are a medium-sized mite, on average 0.4 millimetres or 400 microns long (excluding mouthparts). They are sometimes confused with the flat mites (false spider) family Tenuipalpidae.

Gardeners, farmers and others involved in horticultural industries are encouraged to take notice of spider mites. Samples of suspect mites are welcomed and can be submitted in person or posted to our South Perth Office. Please refer to our web page on sending specimens for identification. Identifications of mites that are of potential biosecurity concern are free of charge.

Grass webbing mite (Oligonychus araneum) under webbing on kikuyu lawn (courtesy of Loreto Housley)

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Life cycle

Female spider mites normally lay eggs on the undersides of leaves. There are four distinct active developmental stages. After hatching, the six-legged larval stage is followed by the protonymph, deutonymph and finally the adult stage, all of which have eight legs. There are quiescent (inactive) intervals between each active stage during which moulting takes place. In the active breeding season, development from egg to adult may vary from one to two weeks or more, depending on species, temperature, host plant, humidity and other factors. Some species, such as Tetranychus, overwinter as adult females while others, such as Panonychus, overwinter as eggs.

Mature males are usually a fifth of the weight of a mature female and, in most species, tend to remain straw-coloured. In some species the females are also straw-coloured. In lighter coloured specimens, ingested food is visible in the stomach sacks, for example, as two spots for Tetranychus urticae (two-spotted mite) or six spots for Eotetranychus sexmaculatus (six-spotted mite). Fully engorged mature females are often darker and more opaque. Colour variation within a species is common, including shades and hues (green/red/brown and combinations).

Two-spotted spider mite (Tetranychus urticae) with ingested food visible in the stomach sacks

Damage

Mites feed primarily on the lower surface of leaves of the host plant, concentrating their activity adjacent to leaf veins. During feeding, they penetrate the leaf by inserting their chelicerae (stylet-like mouthparts) into the parenchyma cells of leaves and suck the cell contents into their body by a 'pharyngeal pump'.

This results in discolouration of leaf tissue, where typical symptoms include yellow spots on the upper side of the leaf due to chlorophyll depletion. Stippling normally occurs around leaf veins, but can cover entire leaves where they can become stunted and deformed. Severe infestations can result in defoliation, reduced quality and yield of fruit, and aesthetic injury, particularly to ornamental plants.

European red mite feeding damage on an apple leaf

Taxonomic characters and diagnostics

Tetranychidae belong to the suborder Prostigmata, where their breathing tubes open to the front of the body. The family includes over 70 genera and about 1200 described species globally, where proper identification relies on detailed study of their anatomy. A current checklist of Tetranychidae mites present in Australia is maintained by Dr Bruce Halliday on the Australian Faunal Directory.

An overview of invasive mites and their identification can be found on the Invasive mite identification: Tools for Quarantine and Plant Protection website.

Proper identification relies on a detailed study of their anatomy. Important taxonomic characters include:

the adeagus (penis)

shape of the lobes on the integumentary striae (fine lines covering the body like fingerprints)

tarsal appendages (shape and number of claws, sometimes modified into tenant hairs on the 'feet')

position and shape of setae (hairs on the body and legs)

shape of the peritremes (breathing tubes).

Presence and absence of spider mites of economic concern in WA

Spider mite species present in Western Australia, and many that are absent but of economic significance, are listed in the Western Australian Organisms List (WAOL).

Oligonychus spider mites present in WA include:

Oligonychus araneum (grass webbing mite)

O. coffeae ( red tea mite)

O. mangiferus (mango spider mite)

O. stickneyi.

Oligonychus spider mite species present in Australia but absent from WA include:

Oligonychus biharensis

O. brevipodus

O. calicicola

O. grypus

O. ilicis

O. milleri

O. palus

O. punicae

O. tiwakae.

Oligonychus spider mite species exotic to Australia of economic importance include:

Oligonychus gossypiii

O. mcgregori

O. sacchari

O. orthius.

Tetranychus spider mite species present in WA include:

Tetranychus urticae (two-spotted mite) - red and straw-coloured forms, wide host range including most important agricultural crops and ornamental plants

T. ludeni (bean spider mite) - sometimes confused with T. desertorum, a species not present in Australia

T. lambi (banana spider mite)

T. bunda

T. fijiensis

T. lintearius*

T. marianae

T. neocaledonicus.

* Not all species are considered pests. T. lintearius was released at Albany in Western Australia as a biocontrol agent against gorse (Ilex europaeus) in 2003.

Tetranychus spider mite species present in Australia but absent from WA include:

Tetranychus rhagodiae

T. dianellae

T. gloveri

T. kanzawai

T. lombardinii

T. evansi.

Tetranychus spider mite species exotic to Australia of economic importance include:

Tetranychus piercei - hosts include bananas, palms, sweet potato

T. truncatus - wide host range

T. phaselus - hosts include beans, cotton, sweet potato

T. puschelii

T. mcdanieli

T. pacificus

T. canadensis

T. schoenei

T. macfarlanei

T. yusti

T. desertorum

T. evansi

T. mexicanus

T. turkestani

T. amicus.

Bryobia spider mites present in Australia but absent from WA include:

Bryobia graminum

B. kissophila

B. vasiljevi.

Other genera for which at least one species has been recorded in WA:

These include the six-spotted mite Eotetranychus sexmaculatus which has been recorded on avocado and grapevine. There is potentially another Eotetranychus species, E. near to pseudomori, the Oriental red mite Eutetranycus orientalis, also known as the citrus brown mite, and the European red mite, Panonychus ulmi, which was first identified in WA in 2005.

European red mite attacks many deciduous fruit crops, especially apple, pear and plum. Petrobia latens (brown wheat mite) and Schizotetranychus baltazari (citrus green mite) have also been recorded from WA.

Species currently in Australia, but not in Western Australia, include of the genus Eotetranychus: E. hudsoni, E. lomandrae, E. pronus, E. pseudomori and E. queenslandicus, and of the genus Eutetranychus: E. acaciae and E. pantopus.

For the genus Panonychus: P. citri and P. elongatus, and in the genus Petrobia, P. harti. The genus Schizotetranychus, namely S. asparagi, S. gahniae, S. russeus and S. sagatus is also represented in Australia, but not in WA.

Species currently exotic to Australia and considered to be of economic importance include Eutetranycus africanus, Schizotetranychus andropogoni, Eotetranychus kankitus and Petrobia tunisiae.

Further reading

Seeman OD & Beard JJ 2011, Identification of exotic pest and Australian native and naturalised species of Tetranychus (Acari: Tetranychidae). Zootaxa 2961, 1–72. www.mapress.com/zootaxa/2011/f/zt02961p072.pdf

Flechtmann CHW & Knihinicki DK, 2002, New species and new record of Tetranychus Dufour from Australia, with a key to the major groups in this genus based on females (Acari: Prostigmata: Tetranychidae). Australian Journal of Entomology 41(2), 118–127.