Thrips (
order
Order, ORDER or Orders may refer to:
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
Thysanoptera) are minute (mostly long or less), slender
insect
Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pa ...
s 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 predators.
Entomologists have
described approximately 6,000 species. They fly only weakly and their feathery wings are unsuitable for conventional flight; instead, thrips exploit an unusual mechanism,
clap and fling
Insects are the only group of invertebrates that have evolved wings and flight. Insects first flew in the Carboniferous, some 350 to 400 million years ago, making them the first animals to evolve flight. Wings may have evolved from appendag ...
, to create lift using an unsteady circulation pattern with transient
vortices near the wings.
Many thrips species are
pests of commercially important crops. A few species serve as
vectors for over 20 viruses that cause
plant disease, especially the
Tospoviruses
''Orthotospovirus'' is a genus of negative-strand RNA viruses, in the family ''Tospoviridae'' of the order ''Bunyavirales,'' which infects plants. Tospoviruses take their name from the species '' Tomato spotted wilt orthotospovirus'' (TSWV) which ...
. Some species of thrips are beneficial as pollinators or as predators of other insects or
mite
Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear e ...
s. In the right conditions, such as in greenhouses, many species can exponentially increase in population size and form large swarms because of a lack of natural predators coupled with their ability to reproduce asexually, making them destructive to crops. In addition to damaging plants, thrips may invade houses and infest household objects such as furniture, bedding and computer monitors – in the latter case by forcing their way in between the
LCD and its glass covering.
Their identification to species by standard morphological characteristics is often challenging.
Etymology
The first recorded mention of thrips is from the 17th century and a sketch was made by Philippo Bonanni, a Catholic priest, in 1691. Swedish entomologist Baron
Charles De Geer
Baron Charles de Geer (the family is usually known as De Geer with a capitalized "De" and is pronounced "de yer"); Finspång in Risinge 30 January 1720 – Stockholm 7 March 1778) was a Swedish industrialist and entomologist.
Life
De Geer, w ...
described two species in the
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
''Physapus'' in 1744 and
Linnaeus in 1746 added a third species and named this group of insects ''Thrips''. In 1836 the Irish entomologist
Alexander Henry Haliday
Alexander Henry Haliday (1806–1870, also known as Enrico Alessandro Haliday, Alexis Heinrich Haliday, or simply Haliday) was an Irish entomologist. He is primarily known for his work on Hymenoptera, Diptera, and Thysanoptera, but worked on a ...
described 41 species in 11 genera and proposed the
order
Order, ORDER or Orders may refer to:
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
name of Thysanoptera. The first monograph on the group was published in 1895 by
Heinrich Uzel who is considered the father of Thysanoptera studies.
The generic and English name ''thrips'' is a direct transliteration of the ancient Greek , ''thrips'', meaning "woodworm". Like some other animal names such as ''sheep'', ''deer'', and ''moose'', in English the word thrips is both the singular and plural
forms, so there may be many thrips or a single thrips. Other common names for thrips include thunderflies, thunderbugs, storm flies, thunderblights, storm bugs, corn fleas, corn flies, corn lice, freckle bugs, harvest bugs, and physopods.
The older group name "physopoda" is with reference to the bladder like tips to the
tarsi of the legs. The name of the order Thysanoptera is constructed from the ancient Greek words , ''thysanos'', "tassel or fringe", and , ''pteron'', "wing", for the insects' fringed wings.
Morphology
Thrips are small
hemimetabolic insects with a distinctive cigar-shaped
body plan. They are elongated with transversely constricted bodies. They range in size from in length for the larger predatory thrips, but most thrips are about 1 mm in length. Flight-capable thrips have two similar, strap-like pairs of wings with a fringe of bristles. The wings are folded back over the body at rest. Their legs usually end in two
tarsal segments with a bladder-like structure known as an "arolium" at the pretarsus. This structure can be
everted by means of
hemolymph
Hemolymph, or haemolymph, is a fluid, analogous to the blood in vertebrates, that circulates in the interior of the arthropod (invertebrate) body, remaining in direct contact with the animal's tissues. It is composed of a fluid plasma in which ...
pressure, enabling the insect to walk on vertical surfaces.
They have compound eyes consisting of a small number of ommatidia and three ocelli or simple eyes on the head.
Thrips have asymmetrical
mouthparts
Mouthparts may refer to:
* The parts of a mouth
** Arthropod mouthparts
The mouthparts of arthropods have evolved into a number of forms, each adapted to a different style or mode of feeding. Most mouthparts represent modified, paired append ...
unique to the group. Unlike the
Hemiptera (true bugs), the right
mandible
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
of thrips is reduced and vestigial – and in some species completely absent.
The left mandible is used briefly to cut into the food plant; saliva is injected and the maxillary stylets, which form a tube, are then inserted and the semi-digested food pumped from ruptured cells. This process leaves cells destroyed or collapsed, and a distinctive silvery or bronze scarring on the surfaces of the stems or leaves where the thrips have fed.
Thysanoptera is divided into two suborders, Terebrantia and Tubulifera; these can be distinguished by morphological, behavioral, and developmental characteristics. Tubulifera consists of a single family,
Phlaeothripidae
Phlaeothripidae is a family of thrips with hundreds of genera. They are the only extant family of the suborder Tubulifera, alongside the extinct family Rohrthripidae and are themselves ordered into two subfamilies, the Idolothripinae with 80 ...
; members can be identified by their characteristic tube-shaped apical abdominal segment, egg-laying atop the surface of leaves, and three "pupal" stages. In the Phlaeothripidae, the males are often larger than females and a range of sizes may be found within a population. The largest recorded phlaeothripid species is about 14 mm long. Females of the eight families of the Terebrantia all possess the eponymous saw-like (see
terebra)
ovipositor on the anteapical abdominal segment, lay eggs singly within plant tissue, and have two "pupal" stages. In most Terebrantia, the males are smaller than females. The family Uzelothripidae has a single species and it is unique in having a whip-like terminal antennal segment.
Evolution
The earliest fossils of thrips date back to the
Permian
The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleo ...
(''
Permothrips longipennis''). By the
Early Cretaceous, true thrips became much more abundant.
[ The extant ]family
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
Merothripidae
Merothripidae is a family of thrips in the order Thysanoptera. There are at least 4 genera and 20 described species in Merothripidae.
Genera
These four genera belong to the family Merothripidae:
* '' Damerothrips'' Hood, 1954
* '' Merothrips'' H ...
most resembles these ancestral Thysanoptera, and is probably basal to the order. There are currently over six thousand species of thrips recognized, grouped into 777 extant and sixty fossil genera.
Phylogeny
Thrips are generally considered to be the sister group to Hemiptera (bugs).
The phylogeny of thrips families has been little studied. A preliminary analysis in 2013 of 37 species using 3 genes, as well as a phylogeny based on ribosomal DNA and three proteins in 2012, supports the monophyly of the two suborders, Tubulifera and Terebrantia. In Terebrantia, Melanothripidae may be sister to all other families, but other relationships remain unclear. In Tubulifera, the Phlaeothripidae and its subfamily Idolothripinae are monophyletic. The two largest thrips subfamilies, Phlaeothripinae and Thripinae, are paraphyletic and need further work to determine their structure. The internal relationships from these analyses are shown in the cladogram.
Taxonomy
The following families are currently (2013) recognized:
* Suborder Terebrantia
:* Adiheterothripidae (11 genera)
:* Aeolothripidae (29 genera) – banded thrips and broad-winged thrips
:* Fauriellidae (four genera)
:* † Hemithripidae (one fossil genus, '' Hemithrips'' with 15 species)
:* Heterothripidae
Heterothripidae is a family of thrips in the order Thysanoptera
Thrips ( order Thysanoptera) are minute (mostly long or less), slender insects with fringed wings and unique asymmetrical mouthparts. Different thrips species feed mostly on p ...
(seven genera, restricted to the New World)
:* † Jezzinothripidae (included by some authors in Merothripidae
Merothripidae is a family of thrips in the order Thysanoptera. There are at least 4 genera and 20 described species in Merothripidae.
Genera
These four genera belong to the family Merothripidae:
* '' Damerothrips'' Hood, 1954
* '' Merothrips'' H ...
)
:* † Karataothripidae (one fossil species, '' Karataothrips jurassicus'')
:* Melanthripidae
Melanthripidae is a family of thrips belonging to the order Thysanoptera
Thrips ( order Thysanoptera) are minute (mostly long or less), slender insects with fringed wings and unique asymmetrical mouthparts. Different thrips species feed mo ...
(six genera of flower feeders)
:* Merothripidae
Merothripidae is a family of thrips in the order Thysanoptera. There are at least 4 genera and 20 described species in Merothripidae.
Genera
These four genera belong to the family Merothripidae:
* '' Damerothrips'' Hood, 1954
* '' Merothrips'' H ...
(five genera, mostly Neotropical and feeding on dry-wood fungi) – large-legged thrips
:* † Scudderothripidae (included by some authors in Stenurothripidae
Stenurothripidae is a family of thrips belonging to the order Thysanoptera
Thrips ( order Thysanoptera) are minute (mostly long or less), slender insects with fringed wings and unique asymmetrical mouthparts. Different thrips species feed ...
)
:* Thripidae
The Thripidae are the most speciose family of thrips, with over 290 genera representing just over two thousand species. They can be distinguished from other thrips by a saw-like ovipositor curving downwards, narrow wings with two veins, and ante ...
(292 genera in four subfamilies, flower living) – common thrips
:* † Triassothripidae (two fossil genera)
:* Uzelothripidae
''Uzelothrips'' is a genus of thrips, and the only genus in the family Uzelothripidae. Up until 2012 it contained a single species, ''U. scabrosus'', known from Belém, Brazil; Brisbane, Australia; Singapore, and Angola. In 2012 a new extinct ...
(one species, '' Uzelothrips scabrosus'')
* Suborder Tubulifera
Phlaeothripidae is a family of thrips with hundreds of genera. They are the only extant family of the suborder Tubulifera, alongside the extinct family Rohrthripidae and are themselves ordered into two subfamilies, the Idolothripinae with 80 ...
:* Phlaeothripidae
Phlaeothripidae is a family of thrips with hundreds of genera. They are the only extant family of the suborder Tubulifera, alongside the extinct family Rohrthripidae and are themselves ordered into two subfamilies, the Idolothripinae with 80 ...
(447 genera in two subfamilies, fungal hyphae and spore feeders)
The identification of thrips to species is challenging as types are maintained as slide preparations of varying quality over time. There is also considerable variability leading to many species being misidentified. Molecular sequence based approaches have increasingly been applied to their identification.
Biology
Feeding
Thrips are believed to have descended from a fungus-feeding ancestor during the Mesozoic, and many groups still feed upon and inadvertently redistribute fungal spores. These live among leaf litter or on dead wood and are important members of the ecosystem
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...
, their diet often being supplemented with pollen. Other species are primitively eusocial and form plant gall
Galls (from the Latin , 'oak-apple') or ''cecidia'' (from the Greek , anything gushing out) are a kind of swelling growth on the external tissues of plants, fungi, or animals. Plant galls are abnormal outgrowths of plant tissues, similar to be ...
s and still others are predatory on mites and other thrips.[ Two species of ''Aulacothrips'', ''A. tenuis'' and ''A. levinotus'', have been found to be ectoparasites on aetalionid and membracid plant-hoppers in Brazil.
''Mirothrips arbiter'' has been found in paper wasp nests in Brazil. The eggs of the hosts including ''Mischocyttarus atramentarius'', ''Mischocyttarus cassununga'' and ''Polistes versicolor'' are eaten by the thrips. Thrips, especially in the family Aeolothripidae, are also predators, and are considered beneficial in the management of pests like the ]codling moth
The codling moth (''Cydia pomonella'') is a member of the Lepidopteran family Tortricidae. They are major pests to agricultural crops, mainly fruits such as apples and pears. Because the larvae are not able to feed on leaves, they are highly ...
s.
Most research has focused on thrips species that feed on economically significant crops. Some species are predatory, but most of them feed on pollen and the chloroplasts harvested from the outer layer of plant epidermal and mesophyll cells. They prefer tender parts of the plant, such as buds, flowers and new leaves. Besides feeding on plant tissues, the common blossom thrips feeds on pollen grains and on the eggs of mites. When the larva supplements its diet in this way, its development time and mortality is reduced, and adult females that consume mite eggs increase their fecundity and longevity.
Pollination
Some flower-feeding thrips pollinate the flowers they are feeding on, and some authors suspect that they may have been among the first insects to evolve a pollinating relationship with their host plants. '' Scirtothrips dorsalis'' carries pollen of commercially important chili pepper
Chili peppers (also chile, chile pepper, chilli pepper, or chilli), from Nahuatl '' chīlli'' (), are varieties of the berry-fruit of plants from the genus ''Capsicum'', which are members of the nightshade family Solanaceae, cultivated for ...
s. Darwin found that thrips could not be kept out by any netting when he conducted experiments by keeping away larger pollinators.
''Thrips setipennis'' is the sole pollinator of '' Wilkiea huegeliana'', a small, unisexual annually flowering tree or shrub in the rainforests of eastern Australia. ''T. setipennis'' serves as an obligate pollinator for other Australian rainforest plant species, including '' Myrsine howittiana'' and '' M. variabilis.'' The genus '' Cycadothrips'' is a specialist pollinator of cycad
Cycads are seed plants that typically have a stout and woody (ligneous) trunk with a crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants of a species are either male o ...
s, the cones of which are adapted for pollination by small insects. Thrips are likewise the primary pollinators of heathers in the family '' Ericaceae'', and play a significant role in the pollination of pointleaf manzanita. Electron microscopy has shown thrips carrying pollen grains adhering to their backs, and their fringed wings are perfectly capable of allowing them to fly from plant to plant.[
]
Damage to plants
Thrips can cause damage during feeding. This impact may fall across a broad selection of prey items, as there is considerable breadth in host affinity across the order, and even within a species, varying degrees of fidelity to a host. Family Thripidae
The Thripidae are the most speciose family of thrips, with over 290 genera representing just over two thousand species. They can be distinguished from other thrips by a saw-like ovipositor curving downwards, narrow wings with two veins, and ante ...
in particular is notorious for members with broad host ranges, and the majority of pest thrips come from this family. For example, '' Thrips tabaci'' damages crops of onion
An onion (''Allium cepa'' L., from Latin ''cepa'' meaning "onion"), also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus '' Allium''. The shallot is a botanical variety of the on ...
s, potato
The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae.
Wild potato species can be found from the southern Uni ...
es, tobacco
Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ...
, and cotton
Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus '' Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose, and can contain minor pe ...
.
Some species of thrips create gall
Galls (from the Latin , 'oak-apple') or ''cecidia'' (from the Greek , anything gushing out) are a kind of swelling growth on the external tissues of plants, fungi, or animals. Plant galls are abnormal outgrowths of plant tissues, similar to be ...
s, almost always in leaf tissue. These may occur as curls, rolls or folds, or as alterations to the expansion of tissues causing distortion to leaf blades. More complex examples cause rosettes, pouches and horns. Most of these species occur in the tropics and sub-tropics, and the structures of the galls are diagnostic of the species involved. A radiation of thrips species seems to have taken place on '' Acacia'' trees in Australia; some of these species cause galls in the petioles, sometimes fixing two leaf stalks together, while other species live in every available crevice in the bark. In ''Casuarina
''Casuarina'' is a genus of 17 tree species in the family Casuarinaceae, native to Australia, the Indian subcontinent, southeast Asia, islands of the western Pacific Ocean, and eastern Africa. It was once treated as the sole genus in th ...
'' in the same country, some species have invaded stems, creating long-lasting woody galls.
Social behaviour
While poorly documented, chemical communication is believed to be important to the group. Anal secretions are produced in the hindgut, and released along the posterior setae as predator deterrents In Australia, aggregations of male common blossom thrips have been observed on the petals of ''Hibiscus rosa-sinensis
''Hibiscus rosa-sinensis'', known colloquially as Chinese hibiscus, China rose, Hawaiian hibiscus, rose mallow and shoeblack plant, is a species of tropical hibiscus, a flowering plant in the Hibisceae tribe of the family Malvaceae. It is widel ...
'' and '' Gossypium hirsutum''; females were attracted to these groups so it seems likely that the males were producing pheromones.
In the phlaeothripids that feed on fungi, males compete to protect and mate with females, and then defend the egg-mass. Males fight by flicking their rivals away with their abdomen, and may kill with their foretarsal teeth. Small males may sneak in to mate while the larger males are busy fighting. In the Merothripidae and in the Aeolothripidae, males are again polymorphic with large and small forms, and probably also compete for mates, so the strategy may well be ancestral among the Thysanoptera.
Many thrips form gall
Galls (from the Latin , 'oak-apple') or ''cecidia'' (from the Greek , anything gushing out) are a kind of swelling growth on the external tissues of plants, fungi, or animals. Plant galls are abnormal outgrowths of plant tissues, similar to be ...
s on plants when feeding or laying their eggs. Some of the gall-forming Phlaeothripidae
Phlaeothripidae is a family of thrips with hundreds of genera. They are the only extant family of the suborder Tubulifera, alongside the extinct family Rohrthripidae and are themselves ordered into two subfamilies, the Idolothripinae with 80 ...
, such as genera '' Kladothrips'' and '' Oncothrips'', form eusocial groups similar to ant colonies, with reproductive queens
Queens is a borough of New York City, coextensive with Queens County, in the U.S. state of New York. Located on Long Island, it is the largest New York City borough by area. It is bordered by the borough of Brooklyn at the western tip of Long ...
and nonreproductive soldier castes.
Flight
Most insects create lift by the stiff-winged mechanism of insect flight with steady state aerodynamics
Aerodynamics, from grc, ἀήρ ''aero'' (air) + grc, δυναμική (dynamics), is the study of the motion of air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dy ...
; this creates a leading edge vortex
In fluid dynamics, a vortex ( : vortices or vortexes) is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved. Vortices form in stirred fluids, and may be observed in smoke rings, whirlpools in ...
continuously as the wing
A wing is a type of fin that produces lift while moving through air or some other fluid. Accordingly, wings have streamlined cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's aerodynamic efficiency is e ...
moves. The feathery wings of thrips, however, generate lift by clap and fling
Insects are the only group of invertebrates that have evolved wings and flight. Insects first flew in the Carboniferous, some 350 to 400 million years ago, making them the first animals to evolve flight. Wings may have evolved from appendag ...
, a mechanism discovered by the Danish zoologist Torkel Weis-Fogh
Torkel Weis-Fogh (25 March 1922 – 13 November 1975) was a Danish zoologist and Professor at the University of Cambridge and the University of Copenhagen. He is best known for his contributions to the understanding of insect flight, especially t ...
in 1973. In the clap part of the cycle, the wings approach each other over the insect's back, creating a circulation of air which sets up vortices and generates useful forces on the wings. The leading edges of the wings touch, and the wings rotate around their leading edges, bringing them together in the "clap". The wings close, expelling air from between them, giving more useful thrust. The wings rotate around their trailing edges to begin the "fling", creating useful forces. The leading edges move apart, making air rush in between them and setting up new vortices, generating more force on the wings. The trailing edge vortices, however, cancel each other out with opposing flows. Weis-Fogh suggested that this cancellation might help the circulation of air to grow more rapidly, by shutting down the Wagner effect which would otherwise counteract the growth of the circulation.
Clap and fling
Insects are the only group of invertebrates that have evolved wings and flight. Insects first flew in the Carboniferous, some 350 to 400 million years ago, making them the first animals to evolve flight. Wings may have evolved from appendag ...
flight mechanism after Sane 2003">
File:Clap and Fling 1- clap 1.svg, Clap 1: wings close over back
File:Clap and Fling 2- clap 2.svg, Clap 2: leading edges touch, wing rotates around
, vortices form
File:Clap and Fling 3 - clap 3.svg, Clap 3: trailing edges close, vortices shed, wings close giving thrust
Apart from active flight, thrips, even wingless ones, can also be picked up by winds and transferred long distances. During warm and humid weather, adults may climb to the tips of plants to leap and catch air current. Wind-aided dispersal of species has been recorded over 1600 km of sea between Australia and South Island of New Zealand.
It has been suggested that some bird species may also be involved in the dispersal of thrips. Thrips are picked up along with grass in the nests of birds and can be transported by the birds.
A hazard of flight for very small insects such as thrips is the possibility of being trapped by water. Thrips have non-wetting bodies and have the ability to ascend a
by arching their bodies and working their way head-first and upwards along the water surface in order to escape.
Thrips lay extremely small eggs, about 0.2 mm long. Females of the suborder
cut slits in plant tissue with their ovipositor, and insert their eggs, one per slit. Females of the suborder
lay their eggs singly or in small groups on the outside surfaces of plants.
, metamorphosing gradually to the adult form. The first two
s) without genitalia; these feed on plant tissue. In the Terebrantia, the third and fourth instars, and in the Tubulifera also a fifth instar, are non-feeding resting stages similar to
e: in these stages, the body's organs are reshaped, and wing-buds and genitalia are formed.