Thrips tabaci Lindeman
Taxonomic placing: Insecta, Hemimetabola, Thysanoptera, Terebrantia, Thripidae.
Common name: Onion thrips.
Geographical distribution: Almost cosmopolitan.
Host plants: Many vegetables, especially onion and garlic, ornamental plants, as well as many weeds and some grasses.
Morphology: The adult is pale yellow to dark brown, about 1-2 mm long, with brownish blotches on the thorax and the median portion. The wings are yellow, fringed with long hairs. The nymphs are whitish to green, about 0.25 mm long, with red eyes.
Life cycle: The onion thrips is parthenogenetic. Females and nymphs occur throughout the year on and around host plants; the wingless males are rare. Females lay about 10-20 eggs and thrust them into leaf and stem tissue. They live for several weeks. Nymphs hatch within 5 to 10 days, and develop through four stages (instars) including a prepupal and a pupal stage, during a period of 15- 30 days. The first two instars are spent on the host plant whereas the later, non-feeding stages hide in the soil. Up to eight generations can occur annually, dependent on the weather.
Economic importance: Most economic injury is to onions, garlic and chives, but many other crops (e.g. eggplant, cabbage, cucumber, tomato) are also affected. Damage is caused by the feeding of nymphs and adults, who scrape the surface of the center leaves and/or terminal buds and suck the exuding plant juices. This results in silvery-white, mottled lesions on the leaves, which become distorted and curl upward; plant growth is delayed. Heavy infestations can kill terminal buds or even entire plants, or may result in undersized bulbs. Injury is more severe under hot, dry conditions. Yields may be reduced by 50-60%, mostly due to pest feeding and also because the resultant wounds allow entrance of disease-causing microorganisms. In addition, T. tabaci transmits Iris yellow spot virus (IYSV), which may cause up to 100% yield losses. Onion thrips has recently become a major pest of onion of increasing global concern.
Monitoring: Yellow or blue sticky traps are used for monitoring thrips migration from their overwintering hosts. As the pest usually flies upwind during migrations, traps are to be placed accordingly. After infestation is confirmed, host plants should be examined to observe the inner, youngest (and most protected) leaves, which the pest prefers. Onion thrips is often located at field borders, near woods or in the vicinity of grain or field crops, from which re-infestations can occur.
Sanitation: Destruction of volunteer plants and crop residues after harvest eliminates many favorable overwintering sites. Since onion thrips populations build up rapidly on cucurbits, crucifers, strawberries, roses and carnations, these crops should not be planted near or rotated with onions.
Plant resistance: onion cultivars are being developed in the USA. Such cultivars have yellow-green foliage, whereas the leaves of susceptible cultivars are blue-green.
Chemical control: Pyrethroids and organophosphates were used to control the pest, which has developed broad-range resistance to most pesticides. Several botanical and chemical insecticides were assayed, the former providing 60% control as compared to over 75% kill by the chemicals, but only for about 7 days. The onion thrips has also become resistant to spinosad.
Biological control. Onion thrips has many natural enemies, including Coccinellidae, Anthocoridae, Neuroptera, spiders and hymenopterous parasitioids, like Ceranisus menes. The entomopathogenic Entomopthora thripidum Samson, Ramakers and Oswald also infects thrips, providing some natural control. The phytoseiids Neoseiulus cucumeris (Oudemans) and Amblyseius swirskii Athias-Henriotare are efficient predators in greenhouses. In a season with low insect pressure, these natural enemies can control the pest.
Ben-Yakir, D. and Chen, M. 2008. Studies of thrips migratory flights in Israel. Acta Phytopathologica et Entomologica Hungarica 43: 243-248.
Diaz-Montano, J., Fuchs, M., Nault, B.A., Fail, J, and Shelton, A.M. 2011 Onion thrips (Thysanoptera: Thripidae): a global pest of increasing concern in onion. Journal of Economic Entomology 104: 1-13.
Diaz-Montano, J., Fuchs, M., Nault, B.A. and Shelton, A.M. 2010 Evaluation of onion cultivars for resistance to onion thrips (Thysanoptera: Thripidae) and Iris yellow spot virus. Journal of Economic Entomology 103: 925-37.
Khaliq, A., Khan, A.A., Afzal, M., Tahir, H.M., Raza, A.M. and Khan, A.M. 2014. Field evaluation of selected botanicals and commercial synthetic insecticides against Thrips tabaci Lindeman (Thysanoptera: Thripidae) populations and predators in onion field plots. Crop Protection 62: 10-15.
Lebedev, G., Abo-Moch, F., Gafni, G/, Ben-Yakir, D. and Ghanim, M. 2013 High-level of resistance to spinosad, evamectin, benzoate and carbosulfan in populations of Thrips tabaci collected in Israel. Pest Management Science 69: 274-277.
Madadi, H., Enkegaard, A., Brodsgaard, H.F., Kharrazi-Pakdel, A., Mohaghegh, J. and Ashouri, A. 2007. Host plant effects on the functional response of Neoseiulus cucumeris to onion thrips larvae. _Journal of Applied Entomology _ 131: 728–733.
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