The chilli thrips, Scirtothrips dorsalis Hood, is an important pest of various vegetable, ornamental and fruit crops in southern and eastern Asia, Africa, and Oceania (Ananthakrishnan 1993, CABI/EPPO 1997, CAB 2003).
Due to its diverse vegetation and subtropical climate, Florida is extremely suitable for the establishment of invasive alien flora and fauna (Ferriter et al. 2006). In the United States, the chilli thrips, Scirtothrips dorsalis Hood, is a relatively new, introduced insect pest in Florida and Texas.
Anaphothrips andreae Karny 1925
Heliothrips minutissimus Bagnall 1919
Neophysopus fragariae Girault 1927
Scirtothrips andreae (Karny)
Scirtothrips fragariae (Girault)
Scirtothrips minutissimus (Bagnall)
Scirtothrips padmae Ramakrishna 1942
Scientists believe that S. dorsalis originated either in Southeast Asia or in the Indian subcontinent, but it is now widely distributed. It is abundant on sacred lotus in Thailand (Mound and Palmer 1981), and on chilli peppers in India (Ramakrishna Ayyar 1932, Ramakrishna Ayyar and Subbiah 1935), where it is also a serious pest of peanuts (Amin 1979, 1980). In Japan, S. dorsalis is a pest of tea and citrus (Kodomari 1978). Scirtothrips dorsalis has been reported from South Africa and the Ivory Coast, and plant quarantine interceptions suggest that this pest is widely distributed across West Africa and is present in East Africa (Kenya).
Although Venette and Davis (2004) suggested that the potential geographic distribution of S. dorsalis in North America might extend from southern Florida north into Canada, a study by Holt (2006) indicates that this species would be troublesome primarily in the southern and Pacific states. These studies signal that it could also become widely established in much of South America, and throughout Central America and Mexico. If this insect becomes widely distributed in the United States it could cause annual crop losses in excess of $3 billion (Holt 2006). According to the Florida Nurserymen and Growers Association, S. dorsalis is one of the thirteen most dangerous, exotic pest threats to the ornamental industry (FNGA 2003).
In the United States, USDA-APHIS inspectors at various ports-of-entry have intercepted S. dorsalis 89 times since 1984 on imported plant materials belonging to 48 taxa (USDA 2004), and most frequently on cut flowers, fruits and vegetables. In Florida, an infestation of S. dorsalis was first reported from Okeechobee County on October 2, 1991, and then from Highlands County on October 10, 1994, with subsequent occurrences in 2004, 2005 and 2007 in various counties of Florida and southeastern Texas.
Known distribution, hosts, and initial discovery dates of S. dorsalis in the Greater Caribbean Region:
Florida - landscape ornamentals and plants in retail (1991, 1994, 2005)
Jamaica - (1995, 2007, 2008 - However, no major outbreaks as of 2008.)
Venezuela - grapevines (2000)
St. Vincent - pepper, amaranth, bean, eggplant, okra, pumpkin, tomato and watermelon; in 8 of 8 districts (as of 2003)
St. Lucia - pepper, cucumber, eggplant, amaranth - found in 4 of 8 districts (as of 2004)
Suriname - hot pepper, Momordica bitter melon, Citrus spp. on Cleopatra rootstock (2004).
Trinidad - pepper, cucurbits, eggplant, okra; in 6 of 8 counties (as of 2004 - not of concern in 2008)
Texas - roses in landscape, on roses and peppers in retail centers (2005)
Barbados - sea island cotton, beans, carrots, peppers, eggplant (2005)
• Puerto Rico - mango (2006)
The small size (< 2 mm) of S. dorsalis life stages and rapid movement make it difficult to detect this insect in fresh vegetation. The very tiny eggs are inserted into soft plant tissues, and the egg stage may last one week. These characteristics increase the chance of transportation of S. dorsalis through international trade of fresh plant materials. Scirtothrips dorsalis life stages occur on all the above-ground plant parts of its hosts, and cause scarring damage due to feeding or the transmission of pathogens (Chang et al. 1995, Seal et al. 2006b).
Generally, chilli thrips are pale colored and the lengths of their first and second instar larvae and the pupae are 0.37-0.39, 0.68-0.71 and 0.78-0.80 mm, respectively. Adults are about 1.2 mm long with dark wings and dark spots forming incomplete stripes which appear dorsally on the abdomen (Seal et al. 2009a).
There are numerous microtrichia and dark transverse antecostal ridges on the abdominal tergites as well as sternites. On the lateral microtrichial fields of the abdominal tergites are three discal setae. The posteromarginal comb on segment VIII is complete. The shaded forewings are distally light in color with straight cilia. The forewings possess an incomplete second vein, or a row of setae with two or three irregular setae in the distal half and a complete first vein.
Of eight antennal segments, I-II are pale and III-VIII are dark. Antennal segments III and IV have forked sense cones. The head and legs are pale. There are three pairs of ocellar setae on the head. The third ocellar seta is between the posterior ocelli. The postocular setae are equal in length. The anteroangular, anteromarginal and discal setae on the pronotum are short and nearly equal in length. Posteromarginial seta II is 1.5 times longer and broader than posteromarginal setae I and III (Skarlinsky 2004).
Accurate and rapid identification of a newly introduced invasive pest is the primary requirement for an effective biological control program. More than 100 species in the genus Scirtothrips have been reported worldwide. Among these, approximately 10 species are serious threats to agricultural production and vegetation in the United States. Members of the genus Scirtothrips can be differentiated from other members of Thripidae by the following features (EPPO 2005):
Surface of pronotum covered with numerous closely spaced transverse striae
Abdominal tergites presents (laterally) consisting of numerous rows of parallel placed rows of tiny microtrichia (cuticular hairs on the surface of the wing membrane)
Sternites possessing marginal setae arising at the posterior margins
Metanotum (tergum of the metathorax) with median pair of setae emerging close to the anterior margin
Life Cycle and Biology
The life cycle stages of S. dorsalis include egg, first and second instar larvae, prepupa, pupa and adult. Gravid females insert the eggs inside plant tissues above the soil surface. The eggs are microscopic (0.075 mm long and 0.070 mm wide), kidney-shaped and creamy white in color (Seal et al. 2009a). The eggs hatch between two to seven days, depending upon temperature. Larvae and adults tend to gather near the mid-vein or borders of the host leaf.
The two larval stages are completed in eight to ten days and the pupal stage lasts for 2.6-3.3 days. The life span of chilli thrips is influenced by the host plant species. For example, at 28°C it takes 11.0 days for a first instar larva to progress to the adult stage on pepper plants and 13.3 days on squash plants. The chilli thrips adult's life span lasts 15.8 days on eggplant, but only 13.6 days on tomato plants (Seal et al. 2009a).
Unlike other thrips, pupae of chilli thrips are generally found on leaves, leaf litter or on the axils of leaves, in curled leaves or under the calyces of flowers and fruits.
Before its arrival in the Western Hemisphere, S. dorsalis was known to infest a wide variety of host-plants belonging to more than 100 plant taxa among 40 families (Mound and Palmer 1981). After its introduction into the Western Hemisphere, S. dorsalis was found to attack additional taxa of plants (Klassen et al. 2008, Osborne 2008, Venette and Davis 2004). While their main wild host-plants belong to the pea family (Fabaceae), such as Acacia, Brownea, Mimosa and Saraca, the chilli thrips has also been recorded as a pest of numerous other economically important host plants in various plant families.
Among the potential economically important hosts of this pest in Western Hemisphere listed by Venette and Davis (2004) are banana, bean, cashew, castor, citrus, cocoa, corn, cotton, eggplant, grapes, litchi, longan, mango, melon, peanut, pepper, poplar, rose, strawberry, sweet potato, tea, tobacco, tomato, and wild yams (Dioscorea spp.). Scirtothrips dorsalis is a significant pest of ornamental plantings in Florida.
Plants in Florida on which S. dorsalisis known to reproduce are as follows:
Antirrhinum majus L. - Liberty Classic white snapdragon
Arachis hypogaea L. - peanut or groundnut grown in greenhouse
Begonia sp. - begonia
Breynia nivosa (W. Bull) Small - snow bush, snow-on-the-mountain
Capsicum annum L. - pepper
Celosia argentea L. - celosia, red fox
Coreopsis sp. - tickseed
Cucumis sativus L. - cucumber
Cuphea sp.- waxweed, tarweed
Duranta erecta L. - golden dewdrop, pigeonberry, skyflower
Euphorbia pulcherrima Willd. - poinsettia
Eustoma grandiflorum (Raf.)Shinn. - Florida blue lisianthus
Ficus elastica 'Burgundy' Roxb. ex Hornem - Burgundy rubber tree
Fragaria x ananassa - strawberry
Gaura lindheimeri Engelm. & Gray - Lindheimer's beeblossom
Gerbera jamesonii H. Bolus ex Hook. f. - Gerber daisy
Glandularia x hybrida (Grönland & Rümpler) Neson & Pruski - verbena
Gossypium hirsutum L. - cotton grown in greenhouse
Hedera helix L. - English ivy
Impatiens walleriana Hook. f. - super elfin white
Lagerstroemia indica L. - crape myrtle
Ligustrum spp. - ligustrum
Ocimum basilicum L. - sweet basil
Pelargonium x hortorum Bailey - geranium
Pentas lanceolata (Forssk.) Deflers - graffiti white
Petunia x hybrida - petunia easy wave red
Pittosporum tobira (Thunb.) W. T. Aiton - variegated pittosporum
Plectranthus scutellarioides (L.) R. - coleus
Plumbago auriculata Lam. - Cape leadwort, plumbago, jamin azul
Ricinus communis L. - castor bean
Rhaphiolepis umbellate (Thunb.) Makino - Yeddo hawthorn
Richardia brasiliensis Gomes - Brazil pusley, tropical Mexican clover, in greenhouse
Rosa sp. - rose
Salvia farinacea Benth. - victoria blue
Shefflera arbicola (Hayata) Merr. - umbrella tree
Tagetes patula L. - marigold
Tradescatia zebrina hort. ex Bosse - wandering jew
Vaccinium corymbosum L. - highbush blueberry
Viburnum odoratissimum var. awabuki (K. Koch) Zabel - sweet viburnum
Viburnum suspensum Lindl. - viburnum
Viola x wittrockiana Gams - Wittrock's violet
Vitis vinifera L. - grapevine
Zinnia elegans Jacq. - zinnia profusion white
(from Klassen et al. 2008, Osborne 2008)
Host list of chilli thrips, Scirtothrips dorsalis among different families of plants
Actinidiaceae: Actinidia deliciosa
Amaranthaceae: Alternanthera sessilis, Amaranthus spp.
Anacardiaceae: Anacardium occidentale, Mangifera indica
Asparagaceae: Asparagus officinalis
Asteraceae: Dahlia pinnata, Imorphotheca aurantiaca, Helianthus annuus
Caprifoliaceae: Viburnum awabuki
Chenopodiaceae: Beta vulgaris
Convolvulaceae: Ipomoea batatas
Cucurbitaceae: Citrullus lanatus, Cucumis melo, Cucumis sativus, Cucurbita pepo
Ebenaceae: Diospyros kaki
Euphorbiaceae: Hevea brasiliensis, Ricinus communis
Fabaceae: Acacia auriculiformis, Acacia brownie, Arachis hypogaea, Brownea spp., Dolichos lablab, Glycine max, Melilotus indica, Mimosa pudica, Phaseolus vulgaris, Saraca minor, Saraca spp., Tamarindus indica, Vigna radiate
Hydrangeaceae: Hydrangea spp.
Liliaceae: Allium cepa, Allium sativum
Lythraceae: Cuphea hyssopifolia
Malvaceae: Gossypium hirsutum
Moraceae: Morus sp.
Myrtaceae: Syzygium samarangense
Nelumbonaceae: Nelumbo lutea, Nelumbo nucifera
Passifloraceae: Passiflora edulis
Poaceae: Zea mays
Polygonaceae: Fagopyrum esculentum
Portulacaceae: Portulaca oleracea
Punicaceae: Punica granatum
Rhamnaceae: Zizyphus mauritiana
Rosaceae: Fragaria chiloensis, Prunus persica, Pyrus spp., Rosa spp., Rubus spp.
Rutaceae: Citrus aurantiifolia, Citrus sinensis
Salicaceae: Populus deltoids
Sapindaceae: Dimocarpus longan, Litchi chinensis, Nephelium lappaceum
Solanaceae: Capsicum annuum, Capsicum frutescens, Lycopersicon esculentum, Nicotiana tabacum, Solanum melongena, Solanum nigrum
Theaceae: Camellia sinensis
Vitaceae: Vitis pteroclada, Vitis vinifera
(from Holtz 2006)
Thrips possesses piercing and sucking mouthparts and causes damage by extracting the contents of individual epidermal cells leading to necrosis of tissue. This changes the tissue color from silvery to brown or black. Chilli thrips create damaging feeding scars, distortions of leaves, and discolorations of buds, flowers and young fruits by feeding on the meristems of the host plant's terminals and on other tender parts above the soil surface. Scirtothrips dorsalis has not been reported feeding on mature host tissues. According to Sanap and Nawale (1987), adult and nymphs of S. dorsalis suck the cell sap of leaves, causing rolling of the leaf upward and leaf size reduction. For example, a heavy infestation of S. dorsalis in pepper plants changes the appearance of the plant to what is called "chilli leaf curl." Appearance of discolored or disfigured plant parts suggests the presence of S. dorsalis.
A severe infestation of chilli thrips makes the tender leaves and buds brittle, resulting in complete defoliation and total crop loss. Infested fruits develop corky tissues (Seal et al. 2006b). Sometimes S. dorsalis infested plants superficially appear like broad mite infested plant. On many hosts, after a heavy infestation chilli thrips also start feeding on the upper surface of leaves.
Symptoms of Damage:
Silvering of the leaf surface
Linear thickenings of the leaf lamina
Brown frass markings on the leaves and fruits
Grey to black markings on fruits often forming a conspicuous ring of scarred tissue around the apex
Fruit distortion and early senescence of leaves
Scirtothrips dorsalis also possesses strong viruliferous behavior for seven recorded viruses. This species transmits chilli leaf curl (CLC) virus, and peanut necrosis virus (PBNV) (Mound and Palmer 1981, Ananthakrishnan 1993). In 2003, Rao et al. found chilli thrips as vectors of tobacco streak virus (TSV) in groundnut crops in India. Recently, in Thailand its role as a vector of three tospoviruses (i.e., melon yellow spot virus (MYSV), watermelon silver mottle virus (WsMoV), and capsicum chlorosis virus (CaCV) in field crops was confirmed (Chiemsombat et al. 2008).
Development of effective management practices for S. dorsalis is still in its infancy. Many recommendations have been suggested by the World Vegetable Center (AVRDC) which could serve as basic management practices for this pest. Management practices include crop rotation, removal of weeds (which may serve as hosts), and supporting the maximum use of natural enemies, including predators and parasites, and rotating insecticides.
Chemical control. Upon the establishment of S. dorsalis in the Caribbean in 2003 there was a paucity of information for effective management of this insect with modern insecticides. In order to impede the development of insecticide resistance it is always advisable to use insecticides from different classes in rotation. Pyrethroids have never been reported to provide effective control against S. dorsalis (Seal et al. 2006a). Various formulations of imidacloprid used as either soil drench or foliar application provide effective control of S. dorsalis without harming natural control agents. Imidacloprid suppresses S. dorsalis populations for many days (Seal et al. 2009b). Spinetoram gives the best result when used as a foliar application and imidacloprid as soil drench (Seal et al. 2008). In addition, these two insecticides when applied as above allow the continuous growth and development of natural enemies of S. dorsalis.
While the above provides general guidelines, for recommended controls see the University of Florida Chilli Thrips website.
Biological control. Various biological control agents, including minute pirate bugs, Orius spp. (Hemiptera: Anthocoridae) and entomopathogenic nematodes, Thripinema spp. (Tylenchida: Allantonematidae), have been reported to effectively control field populations of the chilli thrips. Adults of Orius insidiosus feed on all the life stages of thrips. Because Orius insidiosus also feeds on aphids, mites, moth eggs and pollen, its population does not decline strongly even if thrips populations are drastically reduced. Thripinema species are entomogenous nematodes which parasitize female thrips and make them incapable of laying eggs, leading to the reduction of thrips populations. In addition, they also reduce food consumption of these thrips, resulting in limited feeding damage.
Arthurs et al. (2009) evaluated two phytoseiid mites, Neoseiulus cucumeris and Amblyseius swirskii, as potential biological control agents of the chilli thrips and reported that Amblyseius swirskii can be a promising tool in managing chilli thrips on pepper. Other predators of chilli thrips which are being investigated, but on which adequate practical studies to assess their potential as significant natural enemies of thrips have not been done, include:
lacewings, Chrysoperla spp.
predatory thrips, such as Franklinothrips vespiformis (vespiform thrips), Scolothrips sexmaculatus (sixspotted thrips), Selenothrips rubrocinctus (redbanded thrips), Leptothrips mali (black hunter thrips).
predatory phytoseiid mites, such as Amblyseius spp., Euseius hibisci and Euseius tularensis.
When used alone, the fungal pathogen Beauveria bassiana is not effective in controlling chilli thrips adults or larvae, but produced better result when used in combination with Tricon (an experimental product consisting of borax, orange oil, and biodegradable surfactants) (Kumar, unpublished data).
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