Thrips (singular: thrips; order Thysanoptera), commonly known as thunderflies or thunderbugs, are minute (mostly 1 mm (0.04 in) long or less), slender insects with fringed wings and unique asymmetrical mouthparts. Entomologists have described approximately 7,700 species; they are distributed globally with their food plants. They fly only weakly and their feathery wings are unsuitable for conventional flight; instead, thrips exploit an unusual mechanism, clap and fling, to create lift using an unsteady circulation pattern with transient vortices near the wings. Thrips are a functionally diverse group; many of the known species are fungivorous. A small proportion of the species are serious pests of commercially important crops. Some of these serve as vectors for over 20 viruses that cause plant disease, especially the Tospoviruses. Many flower-dwelling species bring benefits as pollinators, with some predatory thrips feeding on small insects or mites. In the right conditions, such as in greenhouses, invasive 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. Their identification to species by standard morphological characteristics is often challenging.
Naming and etymology The first recorded mention of thrips dates from the 17th century, and a sketch was made by Philippo Bonanni, a Catholic priest, in 1691. Swedish entomologist Baron Charles De Geer described two species in the genus 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 described 41 species in 11 genera and proposed the order name of Thysanoptera. The first monograph on the group was published in 1895 by Heinrich Uzel, who is regarded by Fedor et al. as the father of Thysanoptera studies. The generic and English name thrips is a direct transliteration of the Ancient Greek word θρίψ, thrips, meaning "woodworm". Like some other animal-names (such as sheep, deer, and moose) in English the word "thrips" expresses both the singular and plural, 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" references the bladder-like tips to the tarsi of the legs. The name of the order, Thysanoptera, is constructed from the ancient Greek words θύσανος, thysanos, "tassel or fringe", and πτερόν, pteron, "wing", with reference to the insects' fringed wings.
Description
Thrips are small hemimetabolic insects with a distinctive cigar-shaped body plan. They are elongated with transversely constricted bodies. They range in size from 0.5 to 14 mm (0.02 to 0.55 in) 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 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 unique to the group. Unlike the Hemiptera (true bugs), the right mandible 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. The mouthparts of thrips have been described as "rasping-sucking", "punching and sucking", or, simply just a specific type of "piercing-sucking" mouthparts. 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; 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. Thrips have a global distribution, with more than 6,000 species causing damage to their host plants including crops worldwide.
Evolution
The earliest fossils of thrips date back to the Permian Permothrips longipennis, although it is probably not a member of this group. By the Early Cretaceous, true thrips became much more abundant. The extant family Merothripidae 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. Some thrips were pollinators of the Ginkgoales as early as 110-105 Mya, in the Cretaceous. Cenomanithrips primus, Didymothrips abdominalis and Parallelothrips separatus are known from Myanmar amber of Cenomanian age.
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