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Species Page

western flower thrips

Frankliniella occidentalis
This information is part of a full datasheet available in the Crop Protection Compendium (CPC). Find out more information on how to access the CPC.
©CAB International. Published under a CC-BY-NC-SA 4.0 licence.

Distribution

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Invasive
Origin
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Host plants / species affected

Main hosts

show all species affected
Allium cepa (onion)
Amaranthus palmeri (Palmer amaranth)
Arachis hypogaea (groundnut)
Begonia
Beta vulgaris (beetroot)
Beta vulgaris var. saccharifera (sugarbeet)
Brassica oleracea var. capitata (cabbage)
Capsicum annuum (bell pepper)
Carthamus tinctorius (safflower)
Chrysanthemum morifolium (chrysanthemum (florists'))
Citrus sinensis (sweet orange)
Citrus x paradisi (grapefruit)
Cucumis melo (melon)
Cucumis sativus (cucumber)
Cucurbita maxima (giant pumpkin)
Cucurbita pepo (marrow)
Cucurbitaceae (cucurbits)
Cyclamen
Cynara cardunculus var. scolymus (globe artichoke)
Dahlia
Daucus carota (carrot)
Dianthus caryophyllus (carnation)
Euphorbia pulcherrima (poinsettia)
Eustoma
Ficus carica (common fig)
Fragaria ananassa (strawberry)
Fuchsia
Geranium (cranesbill)
Gerbera jamesonii (African daisy)
Gladiolus (sword lily)
Gladiolus hybrids (sword lily)
Gossypium (cotton)
Gypsophila (baby's breath)
Hibiscus (rosemallows)
Impatiens (balsam)
Kalanchoe
Lactuca sativa (lettuce)
Lathyrus odoratus (sweet pea)
Leucaena leucocephala (leucaena)
Limonium sinuatum (sea pink)
Malus domestica (apple)
Medicago sativa (lucerne)
Mentha piperita (Peppermint)
Orchidaceae (orchids)
Origanum majorana (sweet marjoram)
Petroselinum crispum (parsley)
Phaseolus vulgaris (common bean)
Pisum sativum (pea)
Prunus armeniaca (apricot)
Prunus domestica (plum)
Prunus persica (peach)
Prunus persica var. nucipersica (nectarine)
Purshia tridentata (bitterbrush)
Ranunculus (Buttercup)
Raphanus raphanistrum (wild radish)
Rhododendron (Azalea)
Rosa (roses)
Rumex crispus (curled dock)
Saintpaulia ionantha (African violet)
Salvia (sage)
Secale cereale (rye)
Sinapis arvensis (wild mustard)
Sinningia speciosa (gloxinia)
Solanum lycopersicum (tomato)
Solanum melongena (aubergine)
Solanum tuberosum (potato)
Sonchus (Sowthistle)
Syzygium jambos (rose apple)
Trifolium (clovers)
Triticum aestivum (wheat)
Vaccinium (blueberries)
Vitis vinifera (grapevine)
Zinnia

List of symptoms / signs

Fruit - external feeding
Inflorescence - external feeding
Leaves - external feeding

Symptoms

The symptoms of infestation by F. occidentalis vary widely among the different plants that are attacked. On roses or gerberas with red flowers, or on dark Saintpaulia flowers, feeding damage is readily visible as white streaking. This type of damage is less apparent on white or yellow flowers, and these commonly tolerate very much higher thrips populations with no visible symptoms. Severe infestation leads to deformation of buds if the feeding occurs before these start opening. Capsicums and cucumbers that have been attacked whilst young, show serious distortions as they mature. Leaf damage is variable, but includes silvering due to necrotic plant cells that have been drained of their contents by thrips feeding, malformation due to uneven growth, and a range of spots and other feeding scars. Eggs laid in petal tissue cause a 'pimpling' effect in flowers such as orchids. Egg laying on sensitive fruits such as table grapes, tomatoes and apples leads to the spotting of the skin of the fruit, which reduces the aesthetic value of the fruit (e.g., Venables, 1925). It can also lead to splitting and subsequent entry of fungi. However, the most serious effect of thrips feeding is due to the transmission of tospoviruses into susceptible crops, such as tomatoes, capsicums, lettuce or Impatiens. At least five different tospoviruses are known to be transmitted by western flower thrips and more may well be discovered: Tomato spotted wilt virus (TSWV), Impatiens necrotic spot virus (INSV), Groundnut ringspot virus (GRSV), Chrysanthemum stem necrosis virus (CSNV) and Tomato chlorotic spot virus (TCSV) (Whitfield et al., 2005). These viruses are acquired by the first-instar or early second-instar larvae when feeding on an infected plant, and are then transmitted only later when these larvae develop into the mobile adults; it is not possible for an adult to acquire and then transmit any of these viruses (Moritz et al., 2004). Virus symptoms vary considerably among plants, ranging from the disastrous wilting and collapse of lettuce plants, through a range of leaf mottling and distortions, to ring-spotting on tomato and capsicum fruits. These virus attacks can lead to the total loss of certain crops (see reviews in Kuo, 1996). F. occidentalis also transmits a carmovirus (Pelargonium flower break virus, PFBV) and may transmit an ilarvirus (Tobacco streak virus, TSV) (Jones, 2005).

Prevention and control

Because F. occidentalis breeds so rapidly and virus transmission is so rapid, cultural and biological methods of control should be attempted before turning to the use of pesticides (Stavisky et al., 2002; Reitz et al., 2003; Momol et al., 2004). Chemical control is important and widely practised, but is often constrained by the secretive habits of F. occidentalis, and because populations have been found to develop resistance quickly. A review of chemical methods used in the earlier years of the last century is given by Lewis (1997). Since 1990 more than 50 chemicals have been tested against F. occidentalis, and new ones continue to be added to this list. Spinosyn based insecticides have been found to be some of the most effective chemicals, but local overuse of spinosyns has led to resistance development in F. occidentalis populations (Herron and James, 2005; Bielza et al., 2007; Gao et al., 2012). Similar results have been observed for other classes of insecticides. For example, MacDonald (1995) demonstrated 30-fold differences in susceptibility to malathion among populations of F. occidentalis in the remarkably small area of the southern half of England. A disturbing practice is that of mixing insecticides into 'cocktails' to obtain short-term control enhancement when one insecticide loses efficacy, because of the added risk of longer term resistance that this brings. The range of formulations of insecticides, also the methods of application, that have been used against this pest are very great, but the most effective growers are now placing greater reliance in IPM strategies and ensuring that, when insecticide use is necessary, growers use appropriate rotations of chemistries to forestall the development of resistance (Demirozer et al., 2012; Reitz and Funderburk, 2012).

The basis of good IPM strategies in covered crops is firstly to produce thrips-free conditions through weed control, screening against the pest, and the production of pest-free mother plants. For many years, some growers created their own pests, notably in Chrysanthemum houses, because older plants were used as mother-plants; the apices of each mature plant were removed, rooted and used as the basis for the next crop, although almost every such plant apex contained one live thrips and its eggs. IPM control on mother plants now involves release of the predatory bugs of the genus Orius, as well as predatory mites of the genus Amblyseius or Neoseiulus.

Currently there has been an upsurge in the use of novel insecticides, including soaps and organic products such as extracts of neem trees. One approach has involved the use of UV-blocking films to reduce the flight activity of F. occidentalis (Antignus et al., 1996). Plant breeding to produce strains of crops that are more tolerant to F. occidentalis feeding is also being strongly pursued (reviewed in de Kogel, 1997).

In open field situations, minimizing colonization of the crop by F. occidentalis and fostering development of natural enemy populations has been a successful management approach. UV-reflective mulches disrupt host location by F. occidentalis, and the use of optimal fertility regimes minimizes preference of F. occidentalis for a crop (Brodbeck et al., 2001; Stavisky et al., 2002). Conservation of predators such as Orius insidious can significantly reduce F. occidentalis populations and the incidence of tomato spotted wilt in crops such as capsicum and aubergine (Demirozer et al., 2012).

Post-harvest treatments of commodities can reduce the likelihood of F. occidentalis being transported to countries where it does not yet occur (USDA, 2015).

Impact

F. occidentalis affects commercial plant production in various ways, directly by reducing yield and market quality, whether through feeding damage or by the transmission of virus pathogens, but also indirectly when the mere presence of thrips on a crop is used as a reason for denying it entry to a profitable market.

Systematic national records of crop damage are not kept and growers are reluctant to publicise that they have a pest problem or that they have suffered a large economic loss, so figures for economic impact are hard to obtain. Losses range from total loss of a crop to minor yield reductions, and from serious financial losses as a result of down-grading following superficial damage to fruit to minor reductions in profits through the targeting of less sensitive markets.

In some crops, including rose flowers, strawberries, capsicums and cucumbers, it is the marketable product that is physically attacked by thrips resulting in direct losses due to down-grading. In other crops, attack is more insidious, whether due to leaf damage, or due to the introduction of tospoviruses leading to weaker plants and yield reductions. Sometimes entire crops are lost to virus attacks vectored by thrips, such as Impatiens in glasshouses, and lettuces, capsicums and tomatoes out of doors. The worst attacks are commonly associated with poor crop hygiene, where a grower has failed to recognize the relationship between a susceptible crop and a weed as a source of infection (Cho et al., 1986). Indeed, all too frequently a susceptible crop can be seen newly planted alongside some other crop that is seriously infected but not yet harvested. In contrast, some careful growers mass produce even the most susceptible of crops, such as New Guinea Impatiens, with no losses due to thrips or tospoviruses because their attention to crop hygiene and glasshouse construction is so meticulous.

A vast amount of crop damage has been caused by F. occidentalis since it began to spread in the late 1970s. It is one of the most important insect pests of most glasshouse crops worldwide (Cloyd, 2009) and it is also a major pest of some outdoor crops in warm climates. For example, it is one of the most serious pests of Phaseolus vulgaris in Kenya (Gitonga et al., 2002) and fruiting vegetables in Florida USA (Demirozer et al., 2012; Reitz and Funderburk, 2012).

Losses are usually very high when F. occidentalis first arrives in a country, but go down gradually as growers adjust and new pest management methods are developed. The effects are more serious when thrips populations carry virus. Outbreaks can cause complete crop loss. For example, a grower on the east coast of the USA lost a crop with a wholesale value of US$150,000 after an outbreak of Impatiens necrotic spot virus on Exacum transmitted by F. occidentalis from infected begonias (Daughtrey et al., 1997). A few national estimates of damage have been produced. In the Netherlands, the predicted annual cost to the country of F. occidentalis was estimated to be US$30 million, excluding the effects of Tomato spotted wilt virus (TSWV), and a further US$19 million from TSWV (Roosjen et al., 1998). This included both crop loss and costs of treatment. In Finland, eradication measures from 1987-1990 cost the government US$0.23 million, which was mainly to compensate growers for crop destruction. Even though F. occidentalis has not been eradicated, it is estimated that the cost of its damage to the industry would have been US$1.3 million per year if the eradication campaign had not taken place (Rautapää, 1992). Worldwide, crop damage from tospoviruses transmitted by F. occidentalis probably exceeds US$1 billion per year (Goldbach and Peters, 1994).