Overview
Species in the Thripidae exhibit a wide range of biologies. Some, such as those of
Dendrothrips
and
Scirtothrips
, breed only on leaves, with
Scirtothrips
species apparently particularly dependent on actively dividing young tissues for successful breeding. In contrast, many species of Panchaetothripinae breed most readily on old leaves, and often build up large populations on mature leaves of plants that are water stressed. Some Thripidae species breed only in flowers, such as
Odontothrips
species in Europe and
Odontothripiella
species in Australia, both of which are associated with Fabaceae, and species in these genera are often host specific. Some flower-living Thripidae have been demonstrated to be effective as pollinators on particular species of plants (Mound, 2004; Zerega et al., 2004).
Many Thripidae feed both in flowers and on leaves, and some of these are the most common pest species and tospovirus vectors on crops. Curiously, a few of these pest species, including
Thrips tabaci
and
Frankliniella occidentalis
, may at times act as beneficials, in that they will also feed on spider mites that can be so damaging to plants. A few Thripidae, such as those of the genus
Scolothrips
, are obligate predators of mites.
The Poaceae, including grasses and bamboos, support a very wide range of Thripidae in a variety of genera. Species of
Chirothrips
and related taxa breed in the flowers of grasses (and some sedges), and a single individual will pupate within the glumes that would normally surround a mature seed. Other Thripidae, such as
Anaphothrips
and
Stenchaetothrips
species, feed on grass leaves, but
Limothrips
species seem to feed on both leaves and flowers of grasses.
All Thripidae have two larval and two pupal instars before emerging as adults, and pupation usually occurs at ground level (Heming, 1991). Because of their unusual life cycle, Thysanoptera are sometimes referred to as the Remetabola, a sub-group of the Hemimetabola (Heming, 2003).
Depending on the species, adults may have fully developed wings, or the wings may be no longer than the thorax width (micropterous), or the wings may not be developed at all (apterous) (see, Tyagi et al., 2008). Males are more commonly micropterous or apterous than females, but species such as
Frankliniella fusca
regularly produce micropterous females. Winged forms are unknown in many Thripidae, such as the species of
Aptinothrips
and
Apterothrips
.
Most species of Thripidae are bisexual, although males usually constitute 30% or less of any population. For a few common species, such as the North American Basswood thrips,
Thrips calcaratus
, males have never been found, but individual populations of some other thrips, such as
Thrips tabaci
, commonly lack males.
Description
The Thripidae is a diverse family, in colour, body sculpture and thoracic structure, but can usually be recognised from the structure of the antennae and slender forewings.
The number of antennal segments varies from six to nine among Thripidae, and the sensoria (trichomes) on segments III and IV are characteristically Y-shaped but sometimes simple. Most Thripidae have the antennae 7-segmented or 8-segmented, and the comparatively rare 9-segmented condition in this family is possibly derived secondarily rather than an inherited ancestral condition.
Most Thripidae have three pairs of setae associated with the ocelli, and the pronotum commonly bears two pairs of prominent posteroangular setae, but reduction in setal lengths on the pronotum and forewings has occurred in several unrelated genera. The metanotal median pair of setae usually arise at the anterior margin, but are sometimes near the middle of this sclerite; they are close to the posterior margin only in the members of
Synaptothrips
from South Africa. The posteromarginal cilia on the forewing are wavy (undulating) in most species of this family, and two longitudinal veins are usually visible.
Distribution
Thripidae species can usually be found wherever there is vegetation anywhere in the world. The majority of species occur in the tropics and warm temperate areas, but a few species are known from the subarctic (Greenland) and the subantarctic (Kerguelen and Macquarie Islands). In general, there is a considerable difference between both the size and composition of the thrips faunas of tropical and temperate areas, such as North/South across the land masses of both North America and Australia.
Some Thripidae species are particularly liable to be transported through human trading, such that some grass-living species (Aptinothrips rufus) are effectively worldwide (Mound, 1983). Similarly, Thripidae associated with particular crops are also widespread, such as the gladiolus thrips (
Thrips simplex
) and the onion thrips (
Thrips tabaci
). Some of these expanded distribution patterns probably occured more than 100 years ago, during the period of sailing ships, but the recent increase in air transport of horticultural produce is reflected in the increased distribution of other species, such as
Scirtothrips dorsalis
and
Thrips palmi
.
Europe is the only part of the world for which the Thripidae fauna can be considered reasonably well-known (zur Strassen, 2003), although even on that continent there is a lack of precise host-plant information for many common species. The Thripidae fauna of North America is probably less known than the available literature might imply (Stannard, 1968; Hoddle et al., 2008). Much of the Thripidae fauna of S.E. Asia remains undescribed, and the Thripidae fauna of tropical Africa is effectively unknown.
The fauna of Australia is certainly considerably larger than published figures indicate.
Chirothrips
and, in the cooler southern areas,
Limothrips
are common on grasses; both genera are introduced, the former living in florets and the latter often on leaves.
Stenchaetothrips
biformis
(=
Chloethrips
oryzae
), the oriental rice thrips, is found on grasses in moist habitats in Queensland, and the European wingless species
Aptinothrips
rufus
is abundant on grasses further south. The leaf-living thripine fauna is poorly known;
Anaphothrips
includes native and introduced species,
Chaetanaphothrips
includes two pests on banana and orchid leaves and
Scolothrips
includes one or more introduced predators of leaf mites. A remarkable absence from Australia is
Dendrothrips
, an almost cosmopolitan genus of leaf-feeding species with a large, lyre-shaped, thoracic endofurca associated with jumping.
Ensiferothrips
primus
, a dendrothripine with remarkably broad wing-setae, occurs on
Casuarina
in Australia and New Caledonia.