Frankliniella occidentalis (Pergande)
Common name: Western flower thrips (WFT)
Geographic distribution: Worldwide in temperate regions.
Host plants: Polyphagous, infesting over 500 different plant species.
Morphology: The female is about 1 mm long, larger than the male, with pale forewings. The color of the female varies from yellow to dark brown, being darker at low temperatures, yellowish at higher temperatures. The male is always pale yellow and has a narrower abdomen. The larvae are yellow, becoming paler towards molting.
Life Cycle: A life cycle, from oviposition to adult emergence, may require two weeks in warm weather, to about six weeks in cool weather. The adults live for several weeks; the arrhenotokous females, deposit 50-100 eggs during their lives. They develop through two quiescent, non-feeding pupal stages in the soil, in plant litter or in protected areas on the host plant.
Economic importance: The pest feeds on and breeds in the leaves and flowers. It punctures them, sucking up the exuding sap. Foliage becomes silvery, followed by browning and wilting and withering of the leaf tips, curling and death. The undersides of leaves are spotted with small black specks, which are feces. Flowers become flecked, spotted, and deformed, and buds do not open. WFT infestations result in reductions of the aesthetic quality and marketability of ornamental plants. The pest transmits two Tospoviruses, the impatiens necrotic spot virus (INSV) and the tomato spotted wilt virus (TSWV), both causing serious plant diseases. WFT also feeds on spider mites (Tetranychidae) and may sometimes be a useful biocontrol agent.
Recent molecular studies indicated that WFT consists of two species that cannot be distinguished morphologically, thus the damage described above may be attributed to either, or to both.
Monitoring: Two methods are used to monitor thrips:
- 1. White, yellow or blue sticky traps will attract and trap adults.
- 2. Direct counts in blossoms of fruit crops.
Petunia plants (Petunia x hybrida) are excellent early indicators for WFT presence and for tospoviruses transmission, because petunias are not systemically infected with either virus disease. Presence of silvery leaf scars on other plants is another way of diagnosing WFT presence on plants
Plant resistance : Various efforts are underway to develop cucumber and pepper varieties resistant to WFT.
Chemical control: WFT are difficult to manage with pesticides because they tend to occupy narrow crevices in plant parts, and to feed deep within flowers and buds where they are sheltered from chemicals. Chemical management, mostly with pyrethroids or spinosad (entry/Spinosad), is difficult due to the development of resistance.
Biological control: Several predatory mites, especially the phytoseiid Neoseiulus and the ascid Hypoaspis have successfully been used to control WFT and are in commerce. Predatory bugs (Hemiptera), like Orius spp., are also common. Other antagonists assayed against WFT include nematodes, such as Steinernema feltiae Filipjev, and entomopathogenic fungi, such as Beauveria bassiana (Bals.-Criv.) Vuill. and Metarhizium anisopliae (Met.) Sorokin.
Bautista, R. C., Mau, R. F. L., Cho, J. J. and Custer, D. M. 1995. Potential of tomato spotted wilt tospovirus plant hosts in Hawaii as virus reservoirs for transmission by Frankliniella occidentalis (Thysanoptera: Thripidae). Phytopathology 85: 953-958.
Chambers, R. J., Long, S. and Helyer, B. L. 1993. Effectiveness of Orius laevigatus (Hem.: Anthocoridae) for the control of Frankliniella occidentalis on cucumber and pepper in the United Kingdom. Biocontrol Science and Technology 3: 295-307.
Chyzik, R., Glazer, I. and Klein, M. 1996. Virulence and efficacy of different entomopathogenic nematode species against western flower thrips (Frankliniella occidentalis). Phytoparastica 24: 103-110.
de Kogel, W.J., van der Hoek, M. and Mollema, C. 1997. Variation in performance of western flower thrips populations on susceptible and partially resistant cucumber. Entomologia Experimentalis et Applicata 83: 73-80.
Fery, R. L. and J. M. Schalk. 1991. Resistance in pepper (Capsicum annuum L.) to western flower thrips (Frankliniella occidentalis [Pergande]). HortScience 26: 1073-1074.
Gao, Y., Lei, Z. and Reitz, S.R. 2012. Western flower thrips resistance to insecticides: detection, mechanisms and management strategies. Pest Management Science 68:1111-1121.
Kontsedalov, I., Weintraub, P. G., Horowitz, A.R. and. Ishaaya, I. 1998. Effects of insecticides on immature and adult western flower thrips (Thysanoptera: Thripidae) in Israel. Journal of Economic Entomology 91: 1067-1071,
Montserrat, M., Castañé, C. and Santamaria, S. 1998. Neozygites parvispora (Zygomycotina: Entomophthorales) causing an epizootic in Frankliniella occidentalis (Thysanoptera: Thripidae) on cucumber in Spain. Journal of Invertebrate Pathology 71: 165-168.
Rugman-Jones, P.F., Hoddle, M.S. and Stouthamer. R. 2010.Nuclear-mitochondrial barcoding (NuMB) exposes the global pest Western flower thrips, Frankliniella occidentalis(Thysanoptera: Thripidae) as two sympatric cryptic species in its native California. Journal of Economic Entomology 103: 30-38.
Vernon, R.S. and Gillespie, D.R. 1995. Influence of trap shape, size, and background color on captures of Frankliniella occidentalis (Thysanoptera: Thripidae) in a cucumber greenhouse. Journal of Economic Entomology 88: 288-293.