Tomato red spider mite

Tomato red spider mite (Tetranychus evansi) is a very tiny species of mite. Spider mites are so named because some species spin protective silk webs, similar to those made by spiders.

Tomato red spider mites have 4 life stages, all of which are tiny and require a magnifying glass or hand lens to see clearly. In severe infestations mites, and sometimes their webbing, can be seen by the naked eye on the underside of leaves.

Eggs

• Spherical in shape and less than 0.1mm in size.
• Initially orange to white in colour, they turn grey just before hatching.

Larvae

• 3 pairs of legs.
• Dark to reddish in colour and approximately 0.2mm in size.

Nymphs

• There are 2 nymphal stages.
• 4 pairs of legs.
• Slightly larger than larvae and can be paler or the same colour as adults, varying from orange to brick or dark red.

Adult

• Females are 0.5mm long, oval, orange red in colour with an indistinct dark blotch on each side of the body.
• Males are smaller and yellow-orange-coloured, with pale legs.
• Females can lay up to 200 eggs.

Plant stage and plant parts affected

All above-ground parts of host plants can be affected, but young leaves and shoots are favoured.

Plant damage

Tomato red spider mite feeding causes whitening or yellowing of leaves, which then dry out and eventually fall off. In the case of severe attacks, plant damage progresses very quickly, and hosts may die within 3–5 weeks, if no management actions are taken.

In less intense infestations the top side of leaves appear speckled, as a result of the mites sucking the contents out of individual plant cells. This can reduce the growth rate of plants and can have a negative impact on plant health and crop yield.

When present in low numbers tomato red spider mite infestation may produce no symptoms. As populations increase, plant damage should be more easily seen on leaves.

Tomato red spider mite has been recorded from 44 countries, including: Africa (Algeria, Kenya, Tunisia, Zambia, Zimbabwe, South Africa,), Asia (China, Japan and Taiwan), Europe (Portugal, Spain, Greece, Italy, France), Middle East (Israel, Saudi Arabia, Syria, Turkey), North America (the United States), South America (Argentina, Brazil, Dominican Republic, Virgin Islands), the Caribbean, the Pacific (Hawaii) and Australia.

It was first detected in Australia in 2013, at 3 locations in the Sydney area on solanaceous weed species in New South Wales. In October 2017, T. evansi was reported on tomato (Solanum lycopersicum) and nightshade (Solanum sp.) in a Brisbane backyard in Queensland. The mite has not been reported in any commercial production areas at this time.

Tomato red spider mite is polyphagous, affecting a large variety of host plants (138 plant hosts are listed on Spider Mites Web).

The major hosts are within the Solanaceae, including tomato (Solanum lycopersicum), potato (Solanum tuberosum), eggplant or aubergine (Solanum melongena), tobacco (Nicotiana tabacum) and capsicum (Capsicum annuum).

Other hosts include beans (Phaseolus spp.), citrus (Citrus sp.) cotton (Gossypium spp.), maize (Zea mays) and ornamentals such as roses (Rosa spp.).

The preferred weed host is blackberry nightshade (Solanum nigrum). Other weed hosts include Amaranthus, Chenopodium, Convolvus, Conyza, Diplotaxis, Hordeum murinum, Lavatera and Sonchus.

The life cycle of tomato red spider mite involves the laying of eggs, followed by 4 active life stages (larva, two nymphal stages and adult); with a resting period between each of the active life stages.

Overseas reports indicated that development of tomato red spider mite is favoured by hot dry conditions (minimum temperature 10°C; optimum temperature 34°C). The full life cycle can be completed in 14 days at temperatures of 25°C and above.

In cold climates, tomato red spider mite overwinters as eggs or adult females in the nooks and crannies of tree bark and plant stems, and in leaf litter or the upper soil layer at the base of host plants. In tropical and subtropical areas they may remain active year-round.

Over short distances, mites can be blown by the wind, washed along in irrigation water, and cling to field workers (clothing, tools).

Long distance movement is usually associated with the movement of infested plants or vegetative planting material (bulbs, slips, pups, etc).

The extremely small size of tomato red spider mite makes its detection very difficult.

Tomato red spider mite favours plant hosts in the Solanaceae family. Check solanaceous plants (capsicum, chilli, tomato, eggplant, potato) regularly for signs of leaf damage, then use a hand lens to look for spider mite nymphs and adults on the underside of leaves.

If you see spider mites report them to Biosecurity Queensland on 13 25 23 or phone the Exotic Plant Pest Hotline on 1800 084 881.

• Protect your farm from emergency plant pests
• Understand good farm biosecurity
• Visit the farm biosecurity website