The western flower thrips 'Frankliniella occidentalis'' (Pergande)is an invasive pest insect in agriculture. This species of

thrips Thrips ( order Thysanoptera) are minute (mostly long or less), slender insects with fringed wings and unique asymmetrical mouthparts. Different thrips species feed mostly on plants by puncturing and sucking up the contents, although a few are ...

is native to the

Southwestern United States The Southwestern United States, also known as the American Southwest or simply the Southwest, is a geographic and cultural region of the United States that generally includes Arizona, New Mexico, and adjacent portions of California, Colorado, Ne ...

but has spread to other continents, including Europe, Australia (where it was identified in May 1993), and South America via transport of infested plant material.Kirk, DJ; Terry, IL (2003). The spread of the western flower thrips ''Frankliniella occidentalis'' (Pergande). Agricultural and Forest Entomology 5: 301 – 310.

Morphology

The adult male is about long; the female is slightly larger, about in length. Males are rare, and are always pale yellow, while females vary in color, often by season, from red to yellow to dark brown. Each adult is elongated and thin, with two pairs of long wings. The eggs are oval or kidney-shaped, white, and about long. The nymph is yellowish in color with red eyes.

Instars

The lifecycle of the western flower thrips varies in length due to temperature, with the adult living from two to five or more weeks, and the nymph stage lasting from five to 20 days. Each female may lay 40 to over 100 eggs in the tissues of the plant, often in the flower, but also in the fruit or foliage. The newly hatched nymph feeds on the plant for two of its instars, then falls off the plant to complete its other two instar stages. Nymphs feed heavily on new fruit just beginning to develop from the flower.

Behavioral

Flower-feeding thrips are routinely attracted to bright floral colors, especially white, blue, and yellow, and will land and attempt to feed. Some flower thrips will "bite" humans wearing clothing with such bright colors, though no species feed on blood; such biting does not result in any known disease transmission, but skin irritations are known to occur.Childers CC, Beshear RJ, Frantz G, Nelms M (2005) A review of thrips species biting man including records in Florida and Georgia between 1986-1997. Florida Entomologist: Vol. 88, No. 4 pp. 447–451

Reproduction

Most western flower thrips are female and reproduce by arrhenotokous parthenogenesis; i.e. females can produce males from unfertilized eggs, but females arise only from fertilized eggs.Clarke, G. M., Gross, S., Matthews, M., Catling, P. C., Baker, B., Hewitt, C. L., Crowther, D., & Saddler, S. R. 2000, ''Environmental Pest Species in Australia'', Australia: State of the Environment, Second Technical Paper Series (Biodiversity), Department of the Environment and Heritage, Canberra.

Hosts

It has been documented to feed on over 500 different species of host plants, including a large number of fruit, vegetable, and ornamental crops including ''

Brassica oleracea ''Brassica oleracea'' is a plant species from family Brassicaceae that includes many common cultivars used as vegetables, such as cabbage, broccoli, cauliflower, kale, Brussels sprouts, collard greens, Savoy cabbage, kohlrabi, and gai lan. Its ...

'' (

broccoli Broccoli (''Brassica oleracea'' var. ''italica'') is an edible green plant in the cabbage family (family Brassicaceae, genus ''Brassica'') whose large flowering head, stalk and small associated leaves are eaten as a vegetable. Broccoli is cl ...

, 'Marathon'). The insect damages the plant in several ways. The major damage is caused by the adult ovipositing in the plant tissue. The plant is also injured by feeding, which leaves holes and areas of silvery discoloration when the plant reacts to the insect's saliva. Nymphs feed heavily on new fruit just beginning to develop from the flower. The western flower thrips is also the major vector of

tomato spotted wilt virus Transmission and lifespan TSWV, which is transmitted by thrips, causes serious losses in economically important crops and it is one of the most economically devastating plant viruses in the world. The circulative propagative transmission of T ...

(TSWV), a serious plant disease. It was shown that acquiring TSWV (which only occurs during the larval stages) causes for more feeding in the thrips which makes for a longer life span eventually. Western flower thrips are a year-round pest, but are less destructive during wet weather.

Management

Trapping

WFTs especially like the color

blue Blue is one of the three primary colours in the RYB colour model (traditional colour theory), as well as in the RGB (additive) colour model. It lies between violet and cyan on the spectrum of visible light. The eye perceives blue when obs ...

, being attracted to blue card material and even moreso to blue lights. They are somewhat interested in

yellow Yellow is the color between green and orange on the spectrum of light. It is evoked by light with a dominant wavelength of roughly 575585 nm. It is a primary color in subtractive color systems, used in painting or color printing. In the R ...

, and barely interested in

white White is the lightest color and is achromatic (having no hue). It is the color of objects such as snow, chalk, and milk, and is the opposite of black. White objects fully reflect and scatter all the visible wavelengths of light. White on ...

. Traps can still function even if surrounded with

mesh A mesh is a barrier made of connected strands of metal, fiber, or other flexible or ductile materials. A mesh is similar to a web or a net in that it has many attached or woven strands. Types * A plastic mesh may be extruded, oriented, ex ...

to exclude beneficials such as

hoverflies Hover flies, also called flower flies or syrphid flies, make up the insect family Syrphidae. As their common name suggests, they are often seen hovering or nectaring at flowers; the adults of many species feed mainly on nectar and pollen, while ...

and bees. Commercial semiochemical pheromone lures are also available which can be used in conjunction with blue sticky traps to maximise sticky trap catches of western flower thrips.

Biological controls

Damage can be reduced by growing barriers of nonhost plants around crops and by eliminating reservoir plants, plants to which the thrips are especially attracted, such as jimson weed. The thrips' natural enemies include pirate bugs of genus ''

Orius The genus ''Orius'' (commonly called minute pirate bug) consists of omnivorous bugs in the family Anthocoridae (pirate bugs). Adults are 2–5 mm long and feed mostly on smaller insects, larva and eggs, such as spider mites, thrips, j ...

'' and '' Neoseiulus cucumeris'', a predatory mite species which is the most commonly used biological control agent against western flower thrips in protected crops including cucumber and strawberry. Other agents show promise as

biological pest control Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also invo ...

, including the entomopathogenic fungi ''

Metarhizium robertsii ''Metarhizium robertsii'' formerly known as ''M. anisopliae'', and even earlier as ''Entomophthora anisopliae'' ( basionym) is a fungus that grows naturally in soils throughout the world and causes disease in various insects by acting as a par ...

'' (syn. ''M. anisopliae'') and ''

Beauveria bassiana ''Beauveria bassiana'' is a fungus that grows naturally in soils throughout the world and acts as a parasite on various arthropod species, causing white muscardine disease; it thus belongs to the entomopathogenic fungi. It is used as a biological ...

'',Ansari, M.A., et al. (2007). Control of western flower thrips (''Frankliniella occidentalis'') pupae with ''Metarhizium anisopliae'' in peat and peat alternative growing media. ''Biological Control'' 40:3, 293-297. and the mirid ''

Dicyphus hesperus ''Dicyphus hesperus'' is a species of true bug in the family Miridae. It is a generalist predator of other insects and also feeds on plant tissues. It is native to North America and has been used there in biological control of agricultural pest ...

''.

Genetics

A draft genome assembly is available.

References

External links

WFT fact sheet

PaDIL diagnostic photos

{{Taxonbar, from=Q135374 Thripidae Insect vectors of plant pathogens Agricultural pest insects Fauna of the Southwestern United States Insects described in 1895 Invasive agricultural pests