Thrips

Thrips are tiny insects approximately the size of a sewing needle that eat a variety of plants all around the world. Thrips, also known as Thysanoptera or thunder flies, are sucking insects that can harm plants. When they transmit viruses to plants, though, the consequences can be far severe. Thrips appear on plants as tiny dark slivers. Without a magnifying glass, it's difficult to discern their bodies clearly, but up close, they resemble lobsters. Thrips can infest dwellings and domestic things such as furniture, beds, and computer monitors, making their way in between the LCD and its glass covering.

Taxonomy of Thrips

• The kingdom of thrips insect is Animalia.

• The phylum of thrips is Arthropoda.

• They belong to the class Insecta.

• The order of thrips insect is Thysanoptera.

• There are two suborders of thrips insect Terebrantia and Tubulifera.

There are 17 Families of Thrips Insect Which are as Follows:

• Adiheterothripidae

• Aeolothripidae

• Fauriellidae

• Hemithripidae

• Heterothripidae

• Jezzinothripidae

• Karataothripidae

• Melanthripidae

• Merothripidae

• Scudderothripidae

• Stenurothripidae

• Thripidae

• Triassothripidae

• Uzelothripidae

• Phlaeothripidae

• Rohrthripidae

• There are around 6000 species of thrips as described by the Entomologists.

• The genus of thrips is Thrips.

The Thrips Scientific Name of a Few of the 6000 Species are as Follows:

• Thrips abyssiniae

• Thrips acaciae

• Thrips addendus

• Thrips alatus

• Thrips albogilvus

• Thrips albopilosus

• Thrips aleuritis

• Thrips alius

• Thrips alliorum

• Thrips alni

• Thrips alysii

• Thrips disjunctus

• Thrips distinctus

• Thrips dorax

• Thrips dubius

• Thrips englerinae

• Thrips angusticeps

• Thrips palmi

• Thrips paradoxa

• Thrips simplex

• Thrips tabaci

Morphology of Thrips

• Thrips are hemimetabolic insects with a cigar-shaped body plan.

• They have elongated bodies that are transversely constricted. The larger predatory thrips can be anywhere from 0.5 to 14 mm long, although most thrips are around 1 mm long.

• Thrips with the ability to fly have two sets of strap-like wings with a bristly fringe. At rest, the wings are folded back over the body.

• Their legs normally finish in two tarsal segments, with an "arolium" (a bladder-like structure) at the pretarsus. Hemolymph pressure can be used to evert this structure, allowing the insect to walk on vertical surfaces.

• On the head, they have compound eyes with a modest number of ommatidia and three ocelli or simple eyes.

• Thrips are distinguished by their asymmetrical mouthparts. The right mandible of thrips mouthparts is shortened and vestigial, and in some species completely absent, unlike that of Hemiptera (real bugs).

• The left mandible of thrips mouthparts is momentarily used to cut into the food plant; saliva is injected, the maxillary stylets are inserted, and the semi-digested food is pushed from ruptured cells via the tube. Cells are destroyed or collapse as a result of this process, leaving a unique silvery or golden scarring on the stems or leaves where the thrips have fed.

• Members of the Phlaeothripidae family are distinguished by their tube-shaped apical abdominal segment, egg-laying on the surface of leaves, and three pupal stages. 

• Males in the Phlaeothripidae are frequently larger than females, and populations can have a wide range of sizes. The largest phlaeothripid species ever discovered is roughly 14mm long. 

• Terebrantia females all have the namesake saw-like ovipositor on the anteapical abdominal segment, lay eggs singly within plant tissue, and go through two pupal phases. Males in most Terebrantia are smaller than females.

• The Uzelothripidae family comprises only one species, which is distinguished by its whip-like terminal antennal segment.

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Thrips Life Cycle

• The life cycle of thrips varies depending on the species, region, host plant, and other factors.

• There are over 6,000 different thrips species in the globe, with the tiniest winged insects being thrips. The majority of these species feed on fungi while dwelling in leaf litter or decomposing wood, although some also eat live plants.

• Despite considerable differences across species, each has six stages in its life cycle, as shown in the figure below.

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• The temperature has a significant impact on the length of the lifetime. The life cycle accelerates as the temperature rises.

• Common thrips species that attack greenhouse crops are tiny, measuring about 1-2 mm in length and active in temperatures ranging from 50 to 90 °F (10 to 32 ºC), with an ideal temperature range of 80 to 85 °F (27 to 30 ºC). At temperatures below 50°F (10°C), thrips do not develop.

• Through their ovipositor, female adults lay eggs in live plant tissue. Within 2-4 days, the thrips eggs hatch, starting off the first of two larval phases. The first instar stage lasts 1-2 days, followed by the second instar stage, which lasts 2-4 days following moulting.

• Thrips are ravenous eaters throughout these two stages, punching a hole in a plant cell with their mandible and inserting a stylet to pull out the contents of the cell.

• They feed on the base of flower petals, pollen, young fruit, or fresh sensitive leaves near the terminal ends of stems, depending on the species. They are difficult to spot because they are well concealed and smaller than adults.

• Thrips move to the growth medium near the end of the second instar stage. Thrips go through a prepupal stage during which they begin to build wing pads. This period lasts about a day and a half.

• The pupal stage is when the wings grow, which are made up of long sparse hairs that give them a feather-like look.

• The pupal stage lasts 1-3 days until the wings are fully formed, at which point they emerge as adults from the developing medium.

• In the growing medium, thrips are dormant and do not feed or cause plant harm throughout the prepupal and pupal stages.

• Emerging adults feed on flowers, young leaves, pollen, and developing young fruit as they fly away from the growing medium. 

• Females lay eggs within plant tissues, and adults live for 30-45 days, causing damage to the plant portions they feed on.

• If the conditions are hot, a thrips' life cycle is 21 days or shorter. Depending on the species, females can lay anywhere from 150 to 300 thrips eggs.

• Some thrips can hibernate as eggs in leaf litter or soil outside or under benches in the greenhouse when the weather turns cold.

• During the spring, some thrips can travel from southern tropical regions to the United States and Canada.

Ecology of Thrips Life Cycle

• Thrips hibernate as adults or immature forms in debris, hollow stems, or the earth in colder climates.

• Those that die from the cold each year are replaced by spring migrants from warmer climates.

• Many thrips are more active in the wet seasons than in the dry seasons in the tropics.

• Thrips are sensitive to the relative humidity in several cases. Although larvae are usually found on the underside of leaves or branches in gloomy areas, adults can occasionally be found on the upper side of leaves in bright light.

• The majority of thrips cling to leaf veins or cracks. They are mostly active during the day.

Feeding of Thrips

• During the Mesozoic era, thrips are thought to have descended from a fungus-feeding ancestor, and many species still feed on and unwittingly disseminate fungal spores. These crucial elements of the ecosystem reside in leaf litter or on dead wood, and their diet is typically supplemented by pollen.

• The majority of the research has been done on thrips species that feed on commercially important crops. Some species are predators, but the majority subsist on pollen and chloroplasts are taken from the epidermal and mesophyll cells outer layers. They favour sensitive plant components including buds, blossoms, and young leaves.

• The common bloom thrips feeds on pollen grains and mite eggs in addition to plant tissues. The larva's growth time and mortality are reduced when mite eggs are added to its diet, and adult females who ingest mite eggs have more fertility and lifespan.

Pollination and Leaf Damages by Thrips

• A little flower-feeding thrips pollinate the flowers on which they feed, and some researchers believe they were among the first insects to develop a pollination connection with their hosts.

• When Darwin conducted tests by keeping larger pollinators away, he discovered that no amount of netting could keep thrips out.

• Thrips are the major pollinators of heathers in the Ericaceae family, and they play an important part in point leaf manzanita pollination.

• Thrips have pollen grains adhering to their backs, and their fringed wings are perfectly capable of allowing them to fly from plant to plant, according to electron microscopy.

• During feeding, thrips can cause damage. Because there is such a wide range of host affinity across the order, and even within a species, differing degrees of loyalty to a host, this impact could be felt over a wide range of prey items.

• Some thrips species produce galls, which are nearly invariably found in leaf tissue. Curls, rolls, and folds can occur, as well as changes in tissue expansion that cause leaf blade deformation.

Types of Thrips

Since we have around 6000 different species of trips, let us look into a few of the important types along with the thrips scientific name.

• Thrips Angusticeps 

• They belong to the Thysanoptera order and the Thripidae family of insects. 

• It is a pest of flax, grain, and pea crops.

• Thrips Palmi 

• Thrips palmi is a Thrips genus insect belonging to the Thysanoptera order. Melon thrips is the popular name for it. 

• Melon thrips can harm a variety of ornamental and vegetable crops grown in glasshouses, notably those belonging to the Cucurbitaceae and Solanaceae families, such as cucumber, aubergine, tomato, and sweet pepper. 

• Adults and nymphs eat by sucking the contents of cells from leaves, stems, flowers, and the surface of fruits, resulting in silvery scars and chlorosis on the leaves. Infested plants might become distorted and even die. 

• Although the pest is thought to have originated in Southeast Asia, it has spread throughout Asia and the Pacific, Florida, the Caribbean, South America, Africa, and Australia in recent decades.

• Thrips Tabaci 

• Thrips tabaci is a very small insect species belonging to the genus Thrips and the order Thysanoptera. 

• Onion thrips, potato thrips, tobacco thrips, and cotton seedling thrips are all popular names for this pest. 

• It is an agricultural pest that can harm onion and other plant crops, as well as serve as a vector for plant viruses. 

• Nearly all onion thrips in some populations are female, and males are quite rare. 

• The adult onion thrips measure between 1 and 1.3 mm in length. The body is yellow, yellowish-brown, or brown in colour, with seven segments on the antennae, well-developed wings, and an ovipositor at the tip of the abdomen in females.

• Although the onion thrips is supposed to have originated in the Mediterranean, it may currently be found on every continent except Antarctica.

• Onion, leek, and garlic, brassicaceous plants like cabbage, cauliflower, and broccoli, asparagus, sugarbeet, melon, pumpkin, marrow, and cucumber, strawberry, potato, tobacco, cotton, and many more producing and ornamental plants are all infested by Thrips tabaci.

• In the tropics, the onion thrips are the most important insect pest infecting onion crops. Thrips use their mouthparts to rasp and puncture the plant's surface, preferring new plant development. They then suck out the fluids that drip from the incisions by adding digestive juices. As the plant grows, the damaged areas expand as well, leaving silvery streaks.

• The more thrips there are, the more plant damage there is, lowering the amount of leaf accessible for photosynthesis. At the same time, more water is lost, allowing germs to find a way in. Leaves may wither and the entire plant may appear silvery in badly injured plants; the crop ripens prematurely, but the yield is considerably decreased.

• Thrips Simplex

• Thrips simplex commonly known as Gladiolus thrips is a species of insect belonging to the Thrips genus in the Thysanoptera order. Gladiolus thrips is parasitic thrips that attack gladiolus plants as well as other monocotyledonous plants like lilies, irises, and freesias.

• Thrips simplex is a little insect with a long thin brownish-black body with a pale band at the base of the wings, reaching 2 mm in length.

• The larvae have no wings and are yellow or orange in colour. These thrips, which are frequently seen in groups, reside buried under the leaf and flower sheaths of their host plants, sucking sap.

• Gladiolus, lily, freesia, crocus, and iris are all attacked by the gladiolus thrips, although the gladiolus suffers the most damage. The thrips may survive the winter inside gladiolus corms, causing them to bleed sap from wounds, turn brown, and clump together.

• The sprouting leaves the following year are tunnelled and appear silvery at first, turning brown later. These corms are the principal source of the infestation in growing plants.

• A heavy infestation might cause the plant to grow slowly and fail to blossom. The blossoms can be bruised and disfigured when thrips tunnel into them.

• Brown buds, discoloured or striped blossoms, and bleached or deformed flower spikes are examples of other damage.

Thrips as Pests

• Many thrips are pests of commercial crops because they cause discolouration, malformations, and diminished marketability by feeding on developing flowers or vegetables.

• Plant diseases, such as tospoviruses, are spread by some thrips. Thrips are known to transmit about 20 plant-infecting viruses, however, only about a dozen of the reported species are known to vector tospoviruses. These enveloped viruses are among the most dangerous new plant diseases in the world, with vector species having a disproportionately large impact on human agriculture.

Control of Thrips

• Thrips are difficult to suppress using traditional biological control methods due to their small size and fast rates of reproduction.

• To be effective, predators must be small and slender enough to get into the nooks where thrips hide while eating, as well as prey heavily on eggs and larvae.

• Only two parasitoid Hymenoptera families, the Eulophidae and the Trichogrammatidae, parasitize eggs and larvae.

• Anthocorid bugs of the genus Orius and phytoseiid mites are two other biocontrol agents for adults and larvae.

• Thrips can be killed by biological pesticides such as the fungus Beauveria bassiana and Verticillium lecanii at any stage of their life cycle.

• Thrips can be controlled with insecticidal soap spray. It can be purchased commercially or produced from certain types of domestic soap.

Conclusion

Thrips are small, slender insects with fringed wings that feed by puncturing and sucking the insides of other insects. Some of them, however, feed on a plant's buds and leaves. This results in deformed plant parts or black spots, which are actually thrips faeces. Thrips can also be identified by stippled leaves or blooms that die before opening. We can prune and remove any wounded regions on the plant for controlling thrips. Thrips can be controlled by pruning on a regular basis. Thrips on flowers can be controlled with a moderate insecticide such as insecticidal soap or neem oil, or by trimming the blossoms as soon as signs of damage appear.