Information about Thrips

Thrips, also commonly known as storm flies, storm bugs, thunderflies, thunderbugs, thunderblights, corn flies, corn lice, and physopods, are small insects that belong to the order Thysanoptera. There are approximately 6,000 known species of thrips, and the Thysanoptera order can be divided into 2 suborders, which are distinguishable by developmental, morphological, as well as behavioural characteristics:

• Terebrantia: they have a tube-shaped abdomen with no ovipositor, lay eggs on the surface of leaves, and have 3 pupal stages; this suborder includes almost all the thrips that are considered to be pests;
• and Tubulifera: they have an ovipositor on the abdomen, lay eggs within plant tissue, and have 2 pupal stages.

Description and distribution

Thrips are small insects, generally measuring around 1 mm. Depending on the species, though, the smallest can measure as little a 0.5mm in length, while the largest, predatory thrips, as much as 14mm. They are slender, with an elongated, cigar-shaped body. Colouring varies according to the species. Common plant-feeding thrips are yellow, orange, or amber in colour. The head presents asymmetrical mouthparts, with one mandible being longer than the other. These are mainly used to puncture the outer layer of plants or of animal skin, in preparation for feeding. Attached to the abdomen are 3 pairs of legs, which usually end in 2 tarsal segments, and with a structure known as an “arolium”, which allows thrips to walk on vertical surfaces.
Species of thrips that are capable of flight also have 2 pairs of fringed wings. Interestingly, this is reflected in their name: the Greek “thysanos” means “fringe”, while “pteron” means “wing”. However, even winged thrips are generally not very good flyers, though they can be carried for quite long distances by the wind.
Due to the diversity of plants that they can affect, thrips are quite a cosmopolitan species. They can be distributed from the United States to India, depending on what plants they attack. The most common vegetables or plants attacked are onion, garlic, cauliflower, cabbage, cucumber, squash, melon, tomato, turnip, bean, beets, cotton, as adults and nymphs lacerate the surface tissues of the foliage.

Breeding and dietary information

Female thrips can reproduce sexually or asexually. Most females have a period (lasting from 1 day-1 week, depending on the species), during which eggs mature and before which they cannot mate. Mating can last from minutes to hours.
Thrips are hemimetabolic insects, which means that they undergo an incomplete metamorphosis. As mentioned briefly above, the way females lay eggs depends on the suborder they form part of. Terebrantia females, having no ovipositor, will lay their eggs, alone or in small groups, on the outside surfaces of plants. Tubulifera females, on the other hand, will use their ovipositor to cut slits in plant tissue and then insert their eggs inside, one egg per slit. Eggs are small (around 0.2 mm long) and kidney-shaped. Hatching can occur anytime between 1 day and several weeks. Following this, thrips pass through a short (lasting at most 1 day) pre-pupal stage in which they hide in tight, dark places (crevices on plants, flower buds, leaf litter, loose soil, etc.), do not feed, and are mostly immobile. Most thrips will then construct a pupal cell or a cocoon. Terebrantian thrips go through 1 pupal instar, whereas Tubulifera thrips through 2 instars, during which wings and reproductive structures grow, until finally maturing into adult forms. As is the case with many insects, successful and timely development of younglings is very much dependent upon environmental conditions, such as temperature or nutritional quality of food. Cool weather means development can occur within as much as a month, while hot weather, as little as 14 days. Typically, though, thrips develop into adults within 20 days.
Due to their small size and tendency to spend most of the time in cramped locations, thrips do not have a lot of predators. All those that would want to feed on thrips must be small and slender enough to penetrate the crevices in which they hide, and as a result, they include: aphid wasps, anthocorid bugs (genus Orius), and phytoseiid mites. Only 2 families of parasitoid Hymenoptera are known to parasitize eggs and larvae of thrips: the Eulophidae and the Trichogrammatidae.

Thrips are known to feed on a variety of plants (namely flowers and leaves), which means they are generally considered to be pests. Some species, however, are harmless, feeding on pollen, on chloroplasts harvested from the outer layer of plant cells, or on fungi found in leaf litter or on dead tree branches. Other species of thrips are predatory, feeding on eggs, larvae or on other insects. The actual process of feeding involves puncturing the prey and consuming its insides. In the case of plants, this implies extracting the sap, while in the case of animals, it implies extracting body fluids.

Thrips as pests

While some species of thrips feed on insects that are labelled as pests, thus being considered beneficial, others feed on plants that have commercial value: vegetables such as onions, beans, carrots, squash, etc.; and flowers such as gladioli, roses, etc. In doing so, they can cause tremendous damage, such as discoloration, blackening, deformities, and, subsequently, reduced marketability. Damage also occurs as a result of them laying eggs on fruits and crops. The majority of these harmful thrips come from the family Thripidae.
A second problem associated with thrips is the fact that they can be carriers of plant diseases, with more than 20 viruses (such as the Tospoviruses) being known to be transmitted by them. These viruses are considered to be some of the most damaging plant pathogens around the world, and plants are very easily infected with them.

What’s more, the small size and predisposition towards cramped spaces causes thrips to be very difficult to detect by phytosanitary inspection, which, in turn, has allowed them to expand globally to such an extent that they are now considered to be some of the most invasive species in the world. Under the right environmental conditions, such as those that exist in a greenhouse, thrips can increase in population exponentially, forming large swarms that can be completely devastating. Not only this, but thrips are also capable of easily developing resistance to pesticides. If populations are not controlled and reduced in time, affected flowering plants may lose the ability to produce altogether.
Thrips also invade homes, and some species have been known to bite humans; although no thrips actually feed on blood and none transmit any sort of diseases to humans, skin irritation is common. However, the damage is minor and temporary.

When wanting to prevent thrips from taking over your garden or when you want to eliminate an infestation with these pests, you can follow the steps provided in our relevant articles, about ‘How to get rid of Thrips’ and ways in which you can ‘Prevent infestation with Thrips’. However, keep in mind all the aspects when taking action against thrips, because, as mentioned briefly above, they can also be beneficial. Aside from feeding on insects that are considered to be pests, some species of thrips aid in plant pollination. One particular species, Thrips setipennis, is a pollinator for many rainforest plant species, as well as actually the sole pollinator of a small flowering tree, Wilkiea huegeliana, which can be found in the rainforests of eastern Australia.