Key to Australian Freshwater and Terrestrial Invertebrates

Phylum Arthropoda
Subphylum Hexapoda
Class Insecta
Order Thysanoptera

Common name: thrips

Overview

Thysanoptera, or thrips, are small, slender insects, ranging in length from 0.5�15 mm. They have short antennae, piercing, scraping and sucking mouthparts, adhesive bladders on the last leg (tarsal) segment that enable them to cling to surfaces, and the terminal end of the abdomen may be long and tubular with a ring of long hairs at the tip. Adult thrips may be wingless (apterous) or fully winged (macropterous), their wings narrow, with few veins and, typically, fringed with long hairs.

Distribution and diversity

Thrips are found throughout Australia from arid to temperate and tropical regions. More than 5,500 species of thrips are known worldwide. The Australian fauna comprises 696 described species in 183 genera and five families; at least 60 of these species are introduced from overseas. It is estimated that at least 40% of the native fauna still remains to be described.

Life cycle

Sperm transfer in thrips is direct; however, parthenogenesis occurs in some species. Depending on the species, the female inserts her eggs into plant tissue one by one, glues them to the feeding substrate or scatters them on the ground amongst leaf litter. Larvae resemble small, wingless adults and are relatively immobile unless feeding on ephemeral food sources such as flowers. They moult several times before maturity and pupate near the feeding site or in soil. Typically adults disperse before the eggs hatch, but often in some gall and fungus thrips, several generations co-exist.

Feeding

Depending on the species, thrips feed on the flowers, pollen, leaves, shoots and stems of a wide range of grasses, herbs, shrubs and trees. Some species induce galls on their host plant, and live and feed inside the gall. Other species feed on fungi growing on dead branches, under bark and in leaf litter. A few are predators of eggs, larvae or adults of a variety of insects, mites and nematodes. Thrips feed either by sucking up plant juices created after rasping the surface of the plant, by piercing and sucking out internal plant or arthropod fluids, or by consuming small food particles whole, particularly pollen grains.

Ecology

Thrips are found either associated with plants or in leaf litter. Most are solitary, though they may form large groups in areas where preferred food sources are limited. Some form colonies in galls or folded leaf-shelters. Commonly both winged and wingless species are dispersed to new areas by wind. In Australia, flower thrips are found on Acacia and Eucalyptus flowers. Many thrips species minimise water loss in dry areas by living in galls that they induce or by invading galls formed by other insects. Some plant-feeding species are pests of crops (mostly introduced species) and their feeding not only damages plant tissues, but can transmit viral, bacterial and fungal diseases among plants, e.g. the introduced western flower thrips, Frankliniella occidentalis, is a vector for the significant plant disease, tomato spotted wilt virus.