Photo 1. Warty scaring at the calyx end of the chilli fruit caused by Thrips palmi, while the fruit was still in the bud.
Photo 2. Faint lines of scaring down the chilli fruit from the calyx end caused by Thrips palmi, while the fruit was still in the bud.
Photo 4. Scars on the surface of an eggplant fruit due to feeding of thrips, Thrips palmi, when the fruit was young.
Thrips palmi (but note, no species of palms are host!).
Worldwide. East, South & Southeast Asia, the Caribbean, North & South America, and widespread in the Pacific. It is recorded from Australia, American Samoa, Federated States of Micronesia, Guam, New Caledonia, Palau, Papua New Guinea, Samoa, and Wallis & Futuna.
Recorded on many plant families, including cabbage, cucumber, legumes, potato and many ornamentals and weeds. Important crop hosts are French beans, capsicum, chilli, eggplant, melon, potato, tomato and zucchini.
Thrips have piercing mouthparts and these are used to suck out cell contents. Major damage occurs on the undersides of new or old leaves, especially alongside the midribs and veins. Large numbers of thrips cause the leaves to appear silvery or brown, and to curl upwards, becoming boat-like, stunted and deformed. Fruits, too, are deformed and show feeding scars (Photos 1-4), and may drop prematurely.
Thrips palmi are about 1 mm long, narrow, yellow with two pairs of wings (Photo 5). Eggs are laid in young leaves, flowers and fruits; they hatch in 3-4 days and the nymphs look like adults except that they are about half the size and without wings. There are several stages: two on the host plants, which feed actively like the adults, and two - the pre-pupae and pupae - in the soil, which do not feed. After emergence from the pupae the adults burrow to the soil surface and then climb or fly to host plants. The period from egg laying to adult emergence is 10 to 12 days at 30°C, and 14 to 16 days at 25°C. The adults live for 30-90 days.
Thrips palmi is a major pest. Populations increase rapidly causing severe injury. Plants can be deformed or killed by heavy infestations. There are two types of damage caused by Trips palmi: (i) direct damage caused by feeding, and (ii) indirect damage caused by spreading Tomato spotted wilt (TSWV).
Look for insects that are very small, narrow, and just visible to the naked eye. The adults are yellow, with wings; the nymphs are yellow or white, without wings. Look for the silvering or bronzing of the top surfaces of leaves, especially along the midribs and veins.
The management of Thrips palmi involves reducing the damage from direct feeding, as well as the damage done from spreading TSWV.
Natural enemies are not well recorded for Thrips palmi, although there have been introductions of predatory bugs (Orius spp.) and parasitic wasps to control other species in several countries.
There are varieties of capsicum and tomato that are resistant to TSWV. Use these varieties together with cultural control measures to keep populations of thrips low; otherwise, the resistance may fail as it is controlled by a single dominant gene.
Note, reducing thrips populations by use of appropriate insecticides can help lower virus spread. But insecticides are often of limited value in TSWV control because virus spread from weeds is such an important source of infection. Also, thrips only require a short feeding time before they are able to transmit the virus.
Use insecticides as follows, but note that frequent use of broard spectrum synthetic insecticides may also lead to development of insecticide resistance in thrips populations:
AUTHOR Grahame Jackson & Mani Mua
Information from Waterhouse DF, Norris KR (1987) Biological Control Pacific Prospects. Inkata Press. Photo 1 Guyot J, INRA, Pointe-a-Pitre, Bugwood.org. Photo 2 Plant Protection Service Archive, Plant Protection Service, Bugwood.org.
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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