Thrips imaginis (plague thrips)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- History of Introduction and Spread
- Risk of Introduction
- Hosts/Species Affected
- Host Plants and Other Plants Affected
- Growth Stages
- List of Symptoms/Signs
- Biology and Ecology
- Natural enemies
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Plant Trade
- Wood Packaging
- Impact Summary
- Social Impact
- Detection and Inspection
- Similarities to Other Species/Conditions
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Thrips imaginis Bagnall, 1926
Preferred Common Name
- plague thrips
Other Scientific Names
- Thrips apertus Kelly & Mayne, 1934
- Thrips aureolus Girault, 1928
- Thrips fortis Bagnall, 1926
- Thrips io Girault, 1927
International Common Names
- English: apple blossom thrips; apple thrips; Australian thrips; plague, thrips
- THRIIM (Thrips imaginis)
Summary of InvasivenessTop of page
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Metazoa
- Phylum: Arthropoda
- Subphylum: Uniramia
- Class: Insecta
- Order: Thysanoptera
- Family: Thripidae
- Genus: Thrips
- Species: Thrips imaginis
Notes on Taxonomy and NomenclatureTop of page
In the past in Australia, some reports of crop damage by thrips appear to have confused or misidentified the species that were abundant in flowers, such as T. imaginis, Thrips australis, Thrips tabaci and Frankliniella schultzei. As a result, some early reports of damage may have been attributed to the wrong species. Thrips species are often not distinguished by growers and are collectively described as 'thrips' or 'thrip'. When these species occur together it is not easy to distinguish which is responsible for any damage.
DescriptionTop of page
On emergence, the bodies of the larvae are white to clear with red eyes. The bodies quickly turn yellow to orange. Microscopic features of sclerotization and the lengths of setae can be used to distinguish the species and separate the two instars (Kirk, 1987a; Milne et al., 1997). The larvae grow to a length of approximately 1 mm.
The propupae are whitish with short, forward-pointing antennae and short wing buds. The pupae are also whitish, but the antennae point backwards over the head and the wing buds are longer. Both are approximately 1 mm long.
The adult females vary from pale-yellow through to dark-brown, but are typically golden-brown. The adult males are less variable and are typically pale-yellow. The body size of the adult females is variable, but is typically just over 1 mm long, whereas the males are just under 1 mm long. Like most thrips, the adults have two pairs of strap-like fringed wings. T. imaginis has antennae with seven segments and a wide gap in the row of setae on the first vein of the forewing. In live or freshly killed specimens, the ocelli are red.
DistributionTop of page
The distribution map includes records based on specimens of T. imaginis from the collection in the Natural History Museum (London, UK): dates of collection are noted in the List of countries (NHM, various dates).
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.Last updated: 26 Nov 2020
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|-New South Wales||Present||Native|
|Papua New Guinea||Present|
History of Introduction and SpreadTop of page
Risk of IntroductionTop of page
HabitatTop of page
Hosts/Species AffectedTop of page
Host Plants and Other Plants AffectedTop of page
Growth StagesTop of page
SymptomsTop of page
Feeding damage removes the contents of cells to produce small patches with a silver appearance, an effect known as 'silvering'. On coloured petals, white or silver patches can appear where the pigment has been removed. After feeding, the adults and larvae produce anal droplets that dry to produce small dark spots. These are the same colour as the tissue, but darker, so that the spots on a purple petal would appear dark-purple. However, some flowers can contain large numbers of thrips with few, if any, signs of damage. Feeding at an early stage of bud development can produce stunted or deformed flowers and feeding at the end of flowering can produce stunted and deformed fruit.
Heavy infestations on apple blossom cause brown streaks on the flower, and the stamens and pistils wither (Evans, 1932; Andrewartha and Kilpatrick, 1951; Lloyd, 1973). Blossoms can be destroyed, turning brown and shrivelling without opening. If the flowers open, the petals can be stunted, with small concave petals, and can hang on for days or weeks longer than usual.
On strawberries, large numbers of thrips cause the flowers to fall. They can also cause malformed fruit, known as cat-face damage, but this can also be caused by poor pollination in cool conditions (Houlding, 1995).
T. imaginis is not known to transmit any tospoviruses, such as tomato spotted wilt virus (TSWV) (Day and Irzykiewicz, 1954; Ullman et al., 1997).
T. imaginis and other flower thrips can transmit prunus necrotic ringspot virus (PNRSV) via infected pollen in the laboratory, and there is circumstantial evidence that these thrips may be an important cause of new tree infections in stonefruit (Milne and Walter, 2003).
List of Symptoms/SignsTop of page
|Fruit / abnormal shape|
|Fruit / reduced size|
|Inflorescence / blight; necrosis|
|Inflorescence / discoloration (non-graminaceous plants)|
|Inflorescence / dwarfing; stunting|
|Inflorescence / external feeding|
|Inflorescence / fall or shedding|
|Inflorescence / frass visible|
|Inflorescence / lesions; flecking; streaks (not Poaceae)|
|Leaves / external feeding|
|Leaves / frass visible|
|Whole plant / external feeding|
|Whole plant / frass visible|
Biology and EcologyTop of page
Genetic variation within the species has not been studied. However, the mitochondrial genome has been sequenced and shows several unusual features (Shao and Barker, 2003).
Physiology and Phenology
The adult females vary from pale-yellow through to dark-brown, but are typically golden-brown. Darker forms tend to be larger than the paler ones and are associated with cooler weather (Evans, 1932; Steele, 1935; Kirk, 1984). The colour variation is probably a result of the temperature during the immature stages, but genetic variation cannot be ruled out. The adult males are less variable and are typically pale-yellow. There has been no detailed study of the variation within the species.
The egg stage is followed by two larval instars: one propupal instar and one pupal instar and the adult stage. Populations include both females and males. Fertilized eggs are diploid and produce females, whereas unfertilized eggs are haploid and produce males by arrhenotoky.
The eggs are inserted into the plant tissue, mainly in and around the flowers. A few eggs are laid each day throughout most of the life of the adult females (Andrewartha, 1935). The larvae usually live within the flowers and feed on plant tissues, including pollen. In bright sunlight, they retreat within the flowers and are hard to see, but in dim light and at night they will crawl over the flower and are much more exposed (Kirk, 1984). The mature second-instar larvae drop from the plant and pupate in the soil (Andrewartha, 1934). The propupal and pupal stages are spent in the soil. Following emergence, the adults fly to flowers, where they feed on plant tissues, including pollen. The adults also tend to avoid bright sunlight when in flowers and are less obvious than the adults of Thrips tabaci. However, they fly readily in hot weather when shade temperatures exceed approximately 25°C (Evans, 1932). Although the larvae are usually found within flowers, they can also complete their development on tender leaves (Evans, 1932).
The development rate increases with temperature (Andrewartha, 1936). At 20°C, the egg, larval and pupal stages take 4.4 days, 5.7 days and 5.0 days respectively, whereas at 25°C they take 2.6 days, 3.8 days and 3.1 days. Neither eggs nor larvae develop at temperatures below approximately 8°C. Many generations are completed in a year. The adults live longer at lower temperatures. At 23°C, the adult females live for 23 to 66 days. They do not lay eggs at temperatures less than approximately 8°C (Andrewartha, 1935).
The adults and larvae require a high humidity to survive and soil moisture content is critical to the survival of the pupal stages. For example, at 23°C there is high pupal mortality when the soil moisture as a percentage of field capacity is below 25% or above 85% (Andrewartha, 1934).
The life cycle and population dynamics were studied over many years in Adelaide, South Australia, following large outbreaks in the 1930s (Davidson and Andrewartha, 1948a, b). The species is active throughout the year in the Adelaide area, but is claimed to spend the winter as inactive adults in cooler parts of Australia (Andrewartha and Steele, 1934). The population increases greatly in the spring and early summer (September to December) when many host flowers become available and the soil moisture is suitable for the pupal stages. A population crash in the summer (December to January) follows the peak, when hot, dry weather causes the disappearance of the abundant spring flowers and the soil dries out. There is a small peak in the autumn when the rains return before the numbers drop again over winter.
The size of the population peak in spring is variable, but in some years the species becomes so abundant that the adults are present on virtually all plants. Over 4000 thrips have been recorded in a single rose flower (Zeck and Noble, 1932). These massive outbreaks are the reason for the common name of 'plague thrips'. In these 'thrips years', susceptible crops flowering in the spring may be severely affected and even crops on which T. imaginis does not breed, can be infested by many adults. The size of outbreaks has been predicted accurately from four measures of rainfall and temperature in the preceding autumn and spring. Outbreaks occur across large geographical areas and appear to be particularly favoured by an early start to the growing season of the wild host plants in the previous autumn. The detailed interpretation of the 'Andrewartha-Birch equation' that was used to predict the size of the population peak in the Adelaide area (Andrewartha and Birch, 1954), has proved extremely controversial in the field of population dynamics, but the accuracy of the prediction has not been disputed (Kirk, 1997).
The environmental determinants of the distribution of T. imaginis have not been studied. The species is abundant in parts of south-east Australia with mild winters and hot, dry summers, but it has also been found across the arid centre of Australia wherever Acacia or Maireana were in flower (Mound, 1997). It may not be able to survive cold winters.
T. imaginis is often found in flowers with other species of flower thrips, such as Thrips australis, Thrips tabaci and Frankliniella schultzei. Since the arrival of the western flower thrips, Frankliniella occidentalis in Australia in 1993 (Malipatil et al., 1993), this species has also started to be found in flowers along with T. imaginis (Steiner and Enkegaard, 2002).
T. imaginis can be abundant in the flowers of many native plants in Australia, but its role in the beneficial pollination of native plants is not known (Armstrong, 1979; Kirk, 1984; Williams et al., 2001). During outbreaks, it has been claimed to be so abundant in flowers that it reduces the availability of nectar and pollen for bees and so causes problems for beekeepers (Gosford, 1931; Evans, 1932; Andrewartha and Kilpatrick, 1951).
Natural enemiesTop of page
|Natural enemy||Type||Life stages||Specificity||References||Biological control in||Biological control on|
Notes on Natural EnemiesTop of page
Means of Movement and DispersalTop of page
Adult T. imaginis flies actively. It can be carried long distances on the wind and may even have been transported from Australia to New Zealand by this means (Mound, 1983).
Movement in Trade
In view of the abundance of T. imaginis, it is likely that it will be transported on Australian cut flowers or flowering plants. Specimens have been intercepted in the UK on cut flowers of Grevillea and in the Netherlands on Banksia imported from Australia (Vierbergen, 1999). Thrips can be transported in the flowers of species for which thrips are not considered to be a pest. They can also be found in flowers with no obvious signs of damage.
Plant TradeTop of page
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|Flowers/Inflorescences/Cones/Calyx||adults; eggs; larvae; pupae||Yes||Yes||Pest or symptoms not visible to the naked eye but usually visible under light microscope|
|Growing medium accompanying plants||larvae; pupae||Yes||Yes||Pest or symptoms not visible to the naked eye but usually visible under light microscope|
|Plant parts not known to carry the pest in trade/transport|
|Fruits (inc. pods)|
|Stems (above ground)/Shoots/Trunks/Branches|
|True seeds (inc. grain)|
Wood PackagingTop of page
|Wood Packaging not known to carry the pest in trade/transport|
|Loose wood packing material|
|Processed or treated wood|
|Solid wood packing material with bark|
|Solid wood packing material without bark|
Impact SummaryTop of page
|Fisheries / aquaculture||None|
ImpactTop of page
Although T. imaginis is stated to be a minor pest of many crops in Australia, there are few studies that establish economic damage. Early reports of T. imaginis as a pest of cotton appear to have been based on the misidentification of other species and more recent studies indicate that it is not a pest of cotton (Wilson and Bauer, 1993). T. imaginis has been listed as a pest of citrus, but the current opinion is that it does not cause economic damage to the fruit (Broughton and De Lima, 2002).
Thrips can be abundant (up to 500 per bunch) on waxflowers (Chamelaucium spp.) and other native wild flowers grown for export (Woods et al., 1996; Seaton and Woods, 2003). They do not damage the flowers, but they pose a high quarantine risk if left unchecked.
Although T. imaginis is generally considered as a potential pest, it eats the eggs of the two-spotted spider mites (Tetranychus urticae) and is potentially an important beneficial predator of spider mites on cotton (Wilson et al., 1996).
Social ImpactTop of page
Detection and InspectionTop of page
The adults respond in flight to colours and scents (Kirk, 1984; 1987b), so flying adults could be detected by white, blue or yellow sticky traps.
Similarities to Other Species/ConditionsTop of page
The adults can be readily separated from other similar pest species by a few characteristics that can be seen with a good stereoscopic microscope. The presence of seven antennal segments, as opposed to eight, separates T. imaginis from F. occidentalis and F. schultzei. A forewing first vein with a wide gap in the row of setae, as opposed to an evenly spaced row of setae, separates T. imaginis from T. australis, F. occidentalis and F. schultzei. In live or freshly killed specimens, T. imaginis has red ocelli, whereas T. tabaci has grey or brown ocelli.
Prevention and ControlTop of page
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
T. imaginis is on the EPPO Alert List because it may present a phytosanitary risk for the EPPO region.
Cultural Control and Sanitary Methods
T. imaginis normally migrates into a crop from outside, so cultural control or sanitary methods will have little or no impact. However, the control of flowering weeds in and around orchards may help by removing potential host plants.
Flowering time in relation to peak numbers can affect the amount of damage. Some varieties of apple have been found to be more resistant than others (Evans, 1932).
No biological control measures have been developed against this species.
T. imaginis is still easily controlled with insecticides, such as dimethoate, tau-fluvalinate or spinosad, and several are approved for T. imaginis or thrips in general on a range of crops in Australia.
The postharvest disinfestation of waxflowers was achieved by washing flowers in water with the addition of a non-ionic surfactant or petroleum oil and shaking off the excess. The addition of deltamethrin, fluvalinate or bifenthrin enhanced the control (Seaton et al., 1993).
Early Warning Systems
No early warning system is currently in operation. However, an equation was developed in the 1940s for the Adelaide area of South Australia that accurately predicted the size of outbreaks from four measures of rainfall and temperature in the preceding autumn and spring (Davidson and Andrewartha, 1948b).
Field Monitoring/Economic Threshold Levels
Thrips can be easily monitored in the field by tapping a flower against the palm of the hand and counting the number of thrips that are dislodged. More than 20 thrips per flower are needed to cause damage to apple blossom in the cooler, moist highland districts of New South Wales, whereas only four or five per flower can reduce setting in dry inland districts (Lloyd, 1973). A spray threshold of six to eight per flower following warm dry weather during the pink to full bloom period has been recommended in New South Wales (Johnson et al., 1980). In strawberries in Western Australia, serious damage occurs when there are more than ten thrips per flower (Houlding, 1995). Insecticide treatment when thrips reached a level of 40% of flowers with ten or more adult thrips, kept strawberry fruit damage to below economic threshold levels (Steiner and Enkegaard, 2002). Waxflowers (Chamelaucium spp.) should be treated once the number of thrips exceeds ten per bunch (Seaton and Woods, 2003).
No IPM programmes have been developed.
ReferencesTop of page
Andrewartha HG, 1934. Thrips investigation 5. On the effect of soil moisture on the viability of the pupal stages of Thrips imaginis Bagnall. Journal of the Council for Scientific and Industrial Research Australia, 7:239-244.
Andrewartha HG, 1935. Thrips investigation 7. On the effect of temperature and food upon egg production and the length of adult life of Thrips imaginis Bagnall. Journal of the Council for Scientific and Industrial Research Australia, 8:281-288.
Andrewartha HG; Birch LC, 1954. The distribution and abundance of animals. Chicago, USA: University of Chicago Press.
Andrewartha HG; Kilpatrick DT, 1951. The apple thrips. Journal of Agriculture of South Australia, 54:586-592.
Andrewartha HG; Steele HV, 1934. Thrips investigation 4. Some observations on the fluctuations in the numbers of Thrips imaginis Bagnall, in the vicinity of Melbourne during the period 1932 to 1934. Journal of the Council for Scientific and Industrial Research Australia, 7:234-238.
Andrewartha HV, 1936. Thrips investigation 8. The influence of temperature on the rate of development of the immature stages of Thrips imaginis Bagnall and Haplothrips victoriensis Bagnall. Journal of the Council for Scientific and Industrial Research Australia, 9:57-64.
Armstrong JA, 1979. Biotic pollination mechanisms in the Australian flora - a review. New Zealand Journal of Botany, 17:467-508.
Bagnall RS, 1926. Brief descriptions of new Thysanoptera XVII. Annals and Magazine of Natural History, Series 9, 18:98-114.
Bailey SF, 1936. Thrips attacking Man. Canadian Entomologist, 68:95-98.
Bournier JP; Mound LA, 2000. Inventaire commenté des Thysanoptères de Nouvelle Calédonie. Bulletin de la Société Entomologique de France, 105:231-240.
Broughton S; De Lima F, 2002. Monitoring and control of thrips in citrus. Government of Western Australia Department of Agriculture Farmnote, 7:1-4.
Davidson J; Andrewartha HG, 1948. Annual trends in a natural population of Thrips imaginis (Thysanoptera). Journal of Animal Ecology, 17:193-199.
Davidson J; Andrewartha HG, 1948. The influence of rainfall, evaporation and atmospheric temperature on fluctuations in size of a natural population of Thrips imaginis (Thysanoptera). Journal of Animal Ecology, 17:200-222.
Day MF; Irzykiewicz H, 1954. Physiological studies on thrips in relation to transmission of tomato spotted wilt virus. Australian Journal of Biological Sciences, 7:274-281.
EPPO, 2014. PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://www.eppo.int/DATABASES/pqr/pqr.htm
Evans JW, 1932. The bionomics and economic importance of Thrips imaginis. Pamphlet of the Council for Scientific and Industrial Research Australia, 30:1-48.
Gosford, 1931. Thrip infestation. Australasian Beekeeper, 33:130.
Houlding B, 1995. Mite and insect pests of strawberries. Government of Western Australia Department of Agriculture Farmnote, 71:1-7.
Johnson JF; Penrose LJ; Thwaite WG, 1980. Deciduous fruits spray calendar (volume 20), season 1980-1981. New South Wales, Australia: Department of Agriculture.
Kilpatrick DT, 1955. There is an answer to biennial bearing in apples. Journal of the Department of Agriculture, South Australia, 58:471-474.
Kirk WDJ; Terry LI, 2003. The spread of the western flower thrips Frankliniella occidentalis (Pergande). Agricultural and Forest Entomology, 5:301-310.
Malipatil MB; Postle AC; Osmelak JA; Hill M; Moran J, 1993. First record of Frankliniella occidentalis (Pergande) in Australia (Thysanoptera: Thripidae). Journal of the Australian Entomological Society, 32:378.
Milne JR; Milne M; Walter GH, 1997. A key to larval thrips (Thysanoptera) from granite belt stonefruit trees and a first description of Pseudanaphothrips achaetus (Bagnall) larvae. Australian Journal of Entomology, 36(4):319-326; 15 ref.
Milne JR; Walter GH, 2003. The coincidence of thrips and dispersed pollen in PNRSV-infected stonefruit orchards - a precondition for thrips-mediated transmission via infected pollen. Annals of Applied Biology, 142:291-298.
Mound LA, 1983. Natural and disrupted patterns of geographical distribution in Thysanoptera (Insecta). Journal of Biogeography, 10:119-133.
Mound LA; Gillespie P, 1997. Identification Guide to Thrips Associated with Crops in Australia. Orange, Australia: NSW Agriculture.
Seaton K; Woods B, 2003. Insect control of waxflowers. Government of Western Australia Department of Agriculture Farmnote, 40:1-4.
Seaton KA; Woods WM; Walsh PG, 1993. Postharvest disinfestation of arthropods from field-grown Geraldton wax (Chamelaucium uncinatum Schauer). New Zealand Journal of Crop and Horticultural Science, 21(2):147-151
Shao RenFu; Barker SC, 2003. The highly rearranged mitochondrial genome of the plague thrips, Thrips imaginis (Insecta: Thysanoptera): convergence of two novel gene boundaries and an extraordinary arrangement of rRNA genes. Molecular Biology and Evolution, 20(3):362-370.
Steele HV, 1935. Thrips investigation: some common Thysanoptera in Australia. Pamphlet of the Council for Scientific and Industrial Research, Commonwealth of Australia, 54:1-59.
Steiner M; Enkegaard E, 2002. Progress towards integrated pest management for thrips (Thysanoptera: Thripidae) in strawberries in Australia. Bulletin OILB/SROP, 25:253-256.
Vierbergen G, 1999. Risks of Thysanoptera detected on imported plant products: the Dutch experience. Proceedings: Sixth International Symposium on Thysanoptera, Akdeniz University, Antalya, Turkey, 27 April-1 May, 1998., 157-162; 11 ref.
Williams GA; Adam P; Mound LA, 2001. Thrips (Thysanoptera) pollination in Australian subtropical rainforests, with particular reference to pollination of Wilkiea huegeliana (Monimiaceae). Journal of Natural History, 35:1-21.
Wilson LJ; Bauer LR; Walter GH, 1996. 'Phytophagous' thrips are facultative predators of twospotted spider mites (Acari: Tetranychidae) on cotton in Australia. Bulletin of Entomological Research, 86(3):297-305; 46 ref.
Woods B; Seaton K; Grimm M, 1996. Pests of export wildflowers and proteas. Government of Western Australia Department of Agriculture Farmnote, 1:1-5.
Zeck EH; Noble NS, 1932. Thrips - experiments for the control of Thrips imaginis. Agricultural Gazette of New South Wales, 43:231-236.
Bournier JP, Mound LA, 2000. (Inventaire commenté des Thysanoptères de Nouvelle Calédonie). In: Bulletin de la Société Entomologique de France, 105 231-240.
CABI, Undated. CABI Compendium: Status as determined by CABI editor. Wallingford, UK: CABI
Milne J R, Milne M, Walter G H, 1997. A key to larval thrips (Thysanoptera) from granite belt stonefruit trees and a first description of Pseudanaphothrips achaetus (Bagnall) larvae. Australian Journal of Entomology. 36 (4), 319-326.
NHM, 1979. Specimen record from the collection in the Natural History Museum (London, UK)., London, UK: Natural History Museum (London).
NHM, 1983. Specimen record from the collection in the Natural History Museum (London, UK)., London, UK: Natural History Museum (London).
Distribution MapsTop of page
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