Thrips Totally Explained

Everything about Thrips totally explained

Thrips (Order Thysanoptera) are tiny, slender insects with fringed wings (thus the scientific name, from the Greek thysanos (fringe) + pteron (wing)). Other common names for thrips include thunderflies, thunderbugs, storm flies, and corn lice. Thrips species feed on a large variety of sources both plant and animal by puncturing them and sucking up the contents. A large number of thrips species are considered pests, because they feed on plants with commercial value. Some species of thrips feed on other insects or mites and are considered beneficial, while some feed on fungal spores or pollen. So far around 5,000 species have been described. Thrips are generally tiny (1 mm long or less) and are not good flyers, although they can be carried long distances by the wind. In the right conditions, many species can explode in population and swarm everywhere, making them an irritation to humans.
Like the words sheep or moose, the word thrips is used for both the singular and plural forms. So while there may be many thrips there can also be a solitary thrips. The word thrips is from Greek, meaning wood louse.

Characteristics

Thysanoptera are small hemimetabolic insects. Characteristic to them are the fringed wings and asymmetric sucking mouthparts. Unlike the Hemiptera, they've only one mandibular stylet, or if a second is present it's greatly reduced and non functional. The one fully formed mandibular stylet is used to pierce an entry hole in plant cells or pollen grains, wherein the maxillary stylets can easily enter the cell and suck out the contents. The tarsi are unsegmented or two-segmented and at their tip carry a bladderlike structure (arolium) that can be everted by means of hemolymph pressure enabling the insect to walk on vertical surfaces.

Ecology

Thrips feed by piercing plant cells with their paired maxillary stylets, which form a feeding tube. They feed on hundreds of different crop plants, especially during flowering where they also feed on pollen.
   Many thrips are pests of commercial crops due to the damage caused by feeding on developing flowers or vegetables which causes discoloration, deformities, and reduced marketability of the crop. Thrips in the genera Frankliniella (flower thrips) and Thrips also spread plant diseases through the transmission of viruses, such as Tospoviruses. The western flower thrips, Frankliniella occidentalis, has a worldwide distribution and is considered the primary vector of plant diseases caused by Tospoviruses. Over 20 plant infecting viruses are known to be transmitted by thrips. These enveloped viruses are considered among some of the most damaging of emerging plant pathogens around the world. Virus members include the tomato spotted wilt virus and the Impatiens necrotic spot viruses. Flower thrips are routinely attracted to bright floral colors (esp. white, blue, or yellow), and will land and attempt to feed. It is common for some species (for example, Frankliniella tritici and Limothrips cerealium) to "bite" humans under such circumstances, though no species feed on blood; such biting doesn't result in any known disease transmission but skin irritations are known to occur.
   To survive the winter temperatures most thrips species over-winter as either adults or as pupae under ground litter. A typical flower thrips generation time will be from 7 to 22 days depending on the temperature. The eggs are about 0.2 mm long and reniform (kidney shaped), and may take on average 3 days to hatch. Thrips have 2 larval stages then go through a prepupal and a pupae stage, with the adults taking 1 to 4 days to reach sexual maturity. In the two suborders, the females of the suborder Terebrantia are equipped with an ovipositor which they use to cut slits into plant tissue into which they insert their eggs, one per slit, while females of the suborder Tubulifera lack an ovipositor and lay their eggs singly or in small groups on the outside surface of plants.
   Due to their small size, cryptophilic behavior, and high rate of reproduction, thrips are difficult to control using classical biological control. All predators must be small and slender enough to penetrate the crevices that thrips hide in while feeding, and then prey extensively on eggs and larvae. Only two families of parasitoid hymenoptera are known to parasitize eggs and larvae, the Eulophidae and the Trichogrammatidae. Other biocontrol agents of adults and larvae include aphid wasps, anthocorid bugs of genus Orius, and Phytoseiid mites. For this reason, many growers are occasionally forced to make limited use of pesticides to control thrips populations in the field and in greenhouses.

Evolution and systematics

The earliest fossils of thrips date back to Permian (Permothrips longipennis Martynov, 1935). By the Early Cretaceous true thrips became much more abundant. The following families are currently (2006) recognized:

Suborder Terebrantia ť * Adiheterothripidae Shumsher, 1946 (11 genera)

   * Aeolothripidae Uzel, 1895 (29 genera) - banded thrips and broad-winged thrips ť * Fauriellidae Priesner, 1949 (4 genera)

   * †Hemithripidae Bagnall, 1923 (1 fossil genus, Hemithrips with 15 species) ť * Heterothripidae Bagnall, 1912 (7 genera)

   * † Jezzinothripidae zur Strassen, 1973 (included by some authors in Merothripidae) ť * †Karataothripidae Sharov, 1972 (1 fossil species, Karataothrips jurassicus)

   * Melanthripidae Bagnall, 1913 (6 genera) ť * Merothripidae Hood, 1914 (5 genera) - large-legged thrips

   * † Scudderothripidae zur Strassen, 1973 (included by some authors in Stenurothripidae) ť * Thripidae Stevens, 1829 (292 genera in four subfamilies) - common thrips

   * † Triassothripidae Grimaldi & Shmakov, 2004 (2 fossil genera) ť * Uzelothripidae Hood, 1952 (1 species, Uzelothrips scabrosus)

Suborder Tubulifera ť * Phlaeothripidae (447 genera in two subfamilies)

Trivia

In addition to acting as a crop pest, these insects may also enter the home and distress inhabitants by their presence. Homeowners who move ornamental plants indoors during cold weather may awaken thrips from diapause. When present in large numbers, they can cover wall surfaces, curtains, and windowsills. Their small size also gives them an uncanny ability to find their way into seemingly impenetrable places, such as the inside of watch faces or between the panes of glass on LCD monitors . Once inside, they often become trapped and die, leaving the corpse behind the screen indefinitely. Removal is often only possible if the LCD is dismantled and cleaned.

Footnotes

Further Information

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