Photo 3. Scaring of capsicum fruit. The damage was done when the fruit was much younger and the thrips were enclosed in the flowers.
Photo 8. Adults and larvae of Cuban laurel thrips, Gynaikothrips ficorum, on Ficus. They puncture the leaf surface and pits develop.
Photo 9. Cuban laurel thrips, Gynaikothrips ficorum, on Ficus benjamina, with eggs, nymphs and adults.
Thrips are named after the plants that they live on, e.g., bean thrips, chilli thrips, western flower thrips, melon thrips, onion thrips, tobacco thrips. Some species are predators.
Thrips and Frankliniella species. A number of thrips have been identified on vegetables and flowers in Pacific island countries.
Worldwide. Thrips of different species occur in every country. Those that are common in Oceania are the onion thrips, Thrips tabaci (see Fact Sheet no. 117), and the melon thrips, Thrips palmi (see Fact Sheet no. 106). The western flower thrips, Frankliniella occidentalis (see Fact Sheet no. 183) has not been recorded, but is a threat as it is present in Australia and New Zealand.
Tomato, capsicum, melon (see Fact Sheet no. 106), onion (see Fact Sheet no. 117), and many other crops. Predatory thrips prey on plant-eating thrips and spider mites.
As thrips feed, the cells of the plant collapse forming pits, distortions and brown patches on the leaves (Photo 1); later, the leaves have a silver sheen, or a 'scaring' occurs on the fruits (Photos 2-5). Heavy infestations cause leaves to wilt, dry and die (Photo 4).
Adult thrips are narrow, less than 2 mm long, yellow to black depending on the species, with wings that have long hairs at the margins (Photos 7-9). The wings cover the body when they are not in use. Thrips are difficult to see without a hand lens. The eggs are bean-shaped, white, laid on or inside the plant. The lifecycle has six stages: egg, first and second larva (small, whitish and very active, found mainly on the underside of the leaf), pre-pupa, pupa (both stages occur in the soil in natural cracks), and adult. The pre-pupa and pupa are similar in shape to the larvae, but do not move, feed, and show the developing wings.
Thrips occur all year round, but are particularly active in hot, dry times following heavy rains.
Thrips damage plants in two ways: first, they pierce the cells of the plants they feed on and suck out the juices; and second, they spread viruses. Feeding begins when the leaves are still inside the buds, or fruits are still inside the flowers, and damage is only seen when they expand. It may not be possible to find the thrips on damaged leaves because they have already moved to feed elsewhere. Damaged fruits may not be suitable for market. Leaves may dry out and die early. In Pacific island countries, it is not known if thrips spread viruses.
Elsewhere, thrips (Thrips and Frankliniella species) spread a group of viruses called "tospoviruses" which cause important diseases in tomato (Tomato spotted wilt virus), capsicum, tomato, beans, lettuce and eggplant, flowers, and weeds. The tospoviruses group contains some of the world's most damaging viruses. They are the only insect that spreads these viruses.
Look on the underside of the leaves and inside flowers. The larvae are very difficult to see with the naked eye, but with a hand lens the long slender, black bodies of the adults are easily recognised. Look for black or brown specks where the thrips feed; these are faeces. The presence of faeces is a way of telling thrips from mites.
Several natural enemies feed on thrips. There are predatory thrips, minute pirate bugs (Photos 10&11), predatory mites, lacewing larvae and ladybird beetles (adults and larvae). Note, it is best to avoid pesticides to manage thrips, especially those pesticides that are long lasting, as they will destroy populations of beneficial insects.
It is unlikely that thrips populations will be high enough to justify use of pesticide. In any case, the use of pesticides is likely to do more harm than good, as they will kill natural enemies. Also, thrips tend to hide in sheltered places on plants - in leaf and flower buds or under the "calyx" (see Photo 2) of the fruit - and they are also difficult to reach with pesticides. If pesticides are applied, try plant-derived products (botanical sprays) first, and always try to treat the undersides of the leaves. Do the following:
AUTHORS Suzanne Neave & Grahame Jackson
Photos 4-7 Mani Mua, SPC, Sigatoka Research Station, Fiji. Photo 10 Diane Alston, Utah State University, Bugwood.org. Photo 11 Wikipedia. (http://en.wikipedia.org/wiki/Orius). It is not known if this insect is in Pacific island countries; it is given as an example of this type of bug.
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.
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