Thrips tabaci

Thrips tabaci

The onion thrips or potato thrips, tobacco thrips, cotton seedling thrips (Thrips tabaci Lindeman, 1889) is an insect belonging to the Thripidae family.

Systematic –
From a systematic point of view it belongs to:
Eukaryota domain;
Kingdom Animalia;
Subkingdom Eumetazoa;
Bilateria branch;
Phylum Arthropoda;
Subphylum Hexapoda;
Class Insecta;
Subclass Pterygota;
Exopterygota cohort;
Subcohort Neoptera;
Superorder Paraneoptera;
Section Thysanopteroidea;
Order Thysanoptera;
Suborder Terebrantia;
Thripidae family;
Subfamily Thripinae;
Thrips genre,
Species T. tabaci.
The terms are synonymous:
– Limothrips allii Gillette, 1893;
– Parathrips uzeli Karny, 1907;
– Ramaswamiahi kallarensis Ananthakrishnan, 1960;
– Ramaswamiahiella kallarensis Ananthakrishnan, 1960;
– Thrips adamsoni Bagnall, 1923;
– Thrips bicolor Karny, 1907;
– Thrips brachycephalus Enderlein, 1909;
– Thrips bremnerii Moulton, 1907;
– Thrips communis Uzel, 1895;
– Thrips communis subsp. annulicornis Uzel, 1895;
– Thrips communis subsp. pulla Uzel, 1895;
– Thrips debilis Bagnall, 1923;
– Thrips dianthi Moulton, 1936;
– Thrips dorsalis Bagnall, 1927;
– Thrips flava subsp. obsoleta Uzel, 1895;
– Thrips frankeniae Bagnall, 1926;
– Thrips hololeucus Bagnall, 1914;
– Thrips indigenus Girault, 1929;
– Thrips mariae Cotte, 1924;
– Thrips seminiveus Girault, 1926;
– Thrips solanacearum Portchinski, 1883;
– Thrips solanaceorum Widgalm, 1883;
– Thrips tabaci f. atricornis Priesner, 1927;
– Thrips tabaci f. irrorata Priesner, 1927;
– Thrips tabaci f. nigricornis Priesner, 1927.

Geographic Distribution and Habitat –
Thrips tabaci is an insect that appears to have originated in the Mediterranean region, but is now found on every continent except Antarctica. It infests a wide range of host plants including onion, leek and garlic, brassicaceous plants such as cabbage, cauliflower and broccoli, asparagus, sugar beet, melon, pumpkin, courgette and cucumber, strawberry, potato, tobacco, cotton and many fruiting plants and ornamental plants.
It is quite polyphagous and also widespread in Italy.
This thrips was the first identified vector for tomato spotted wilt virus, reported in 1927. There are currently a few populations identified that are unable to transmit tomato spotted wilt virus, probably due to genetic spread in the global population.

Morphology –
Thrips tabaci is an insect which, in the adult stage, measures approximately 1-2 mm in length.
The body has a variable shade from yellow, yellowish-brown or brown.
The antennas are made up of seven segments; the wings are elongated, narrow and finely fringed; they are well developed and the females have an ovipositor at the tip of the saw-shaped abdomen.
In some populations, almost all individuals are female and males are very rare.
The larvae are light green, almost white or yellowish, with a large head and bright red eyes.
The eggs are initially white, then turn orange.
The prepupal and pupal stages are recognized by the immature wings (wing buds) in development. Compared to the prepupa, the pupa has longer and more developed wing buds and longer antennae, carried curved above the head.

Aptitude and biological cycle –
Thrips tabaci is a polyphagous insect widespread throughout the world, which often affects cultivated plants.
The female inserts her saw-shaped ovipositor into the plant tissues and lays her eggs under the epidermis. The eggs, which are laid on leaves, flower petals and the soft parts of stems, hatch in four or five days.
Newly emerged larvae suck sap from plant tissues.
There are two larval stages lasting about nine days in total, followed by the non-feeding prepupal and pupal stages which last four to seven days in total. The adult survives for two or three weeks during which the females lay around eighty eggs. Most eggs are unfertilized and are produced by parthenogenesis.
In warmer climates it reproduces throughout the year; in the colder ones it overwinters in plant debris and becomes active again in spring.
T. tabaci pupates in the soil; nevertheless the pupae can also be found on leaves, in flowers or in other sheltered places.
In total, Thrips tabaci develops in six stages: egg, two larvae, prepupa, pupa and finally the adult insect.
In the prepupal and pupal stages, the larvae do not feed and only move if disturbed.
In populations of different areas, the ratio of males to females varies. A male-to-female ratio of 1 male to 2 females has been recorded in central Spain and 1 male to 6 females in Colorado. In contrast, counts of up to 1 male for every 300 females have been recorded in Sudan, and in Hawaii a collection of over 5000 specimens contained only 5 males in total. Over the years, no males have been reported in some collections from France, Japan, Taiwan and India. A literature study published in 1990 suggested a correlation between longitude and male population numbers, with the highest male counts occurring in the Western Hemisphere.

Ecological Role –
Thrips tabaci is a polyphagous insect that attacks, as mentioned, various plants; among these: onion, leek and garlic, brassicaceous plants such as cabbage, cauliflower and broccoli, asparagus, sugar beet, melon, pumpkin, courgette and cucumber, strawberry, potato, tobacco, cotton and many fruiting plants and ornamental plants. In the greenhouse it attacks cucurbits, tomatoes, peppers, aubergines, roses, chrysanthemums, gerberas, carnations, and many others.
The damage occurs on the leaves and flowers and is due to the trophic bites of all mobile forms, furthermore damage can also occur due to oviposition.
The stings cause a typical silvering on the leaves; this is preceded by localized chlorotic alterations and is followed by punctuated necrosis.
Some damage can also be caused by oviposition made inside the leaf tissues, where they cause sometimes very evident necrosis.
The damage on the flowers can be very serious and consists of more or less localized deformations and depigmentations.
The affected organs may also deform slightly and be subject to more or less intense drying, depending on the intensity of the attack.
In the event of severe attacks, in addition to the direct damage described above, slowing down of metabolic activity may also occur (less gaseous exchange which slows down photosynthesis) and aesthetic damage to the vegetation, due to the large quantity of excrement and exuviae deposited on the attacked organs.
Finally, Thrips tabaci is also a direct or indirect vector of serious infections, especially viruses.
The fight against this insect is carried out both chemically and biologically.
In chemical control, different products are used, depending on the crops to be treated due to the different registrations of the active ingredients.
In any case, action is taken at the first infestations, carrying out any monitoring of the population with blue or white chromotropic traps, carrying out at least 2 close treatments, approximately 10 days.
As regards biological control, this must increasingly make use of the principles of agroecology through crop biodiversification and the introduction of parasitoids and natural insect parasites.
Some interventions have already been tested with the breeding of some species of Orius (Rincoti Anthocoridae) for the biological control in greenhouses, against Thrips on horticultural crops (Aubergine and Cucumber) and flower crops (Gerbera); Orius are active predators of mobile forms.
Furthermore, the use of Chrysoperla carnea was made which, although not a specific predator of thrips, also shows a certain activity against them.
Finally, for some years, in experimental tests, some phytoseiid mites (Amblyseius cucumeris and Amblyseius barkeri) have been used against thrips of which they are active predators; these mites have demonstrated an excellent action in containing the populations of the phytophagous.

Guido Bissanti

Sources
– Wikipedia, the free encyclopedia.
– GBIF, the Global Biodiversity Information Facility.
– Russo G., 1976. Agricultural Entomology. Special Part. Liguori Editore, Naples.
– Pollini A., 2002. Manual of applied entomology. Edagricole, Bologna.
– Tremblay E., 1997. Applied entomology. Liguori Editore, Naples.

Photo source:
– https://www.artportalen.se/MediaLibrary/2021/10/3d94539a-2dcf-46b0-8f28-2d983fea37ea_image.jpg