Species of Phlaeothripidae are particularly diverse in their biologies. Idolothripinae are all considered to feed on fungal spores, and members of Elaphrothrips and related genera have a specialised spore-crushing device in the foregut. In the Phlaeothripinae, members of the “Phlaeothrips lineage” are essentially fungus feeders, presumably on fungal hyphae. Fungus feeding is commonly associated with considerable sexual dimorphism, such that males are larger than females and commonly exhibit allometry in various structures (Mound, 2005). Such males have been shown to indulge in male/male combat, and to compete for resources and the attention of females (Crespi, 1988).
Species in the “Liothrips lineage” are leaf-feeding, and many of these are involved in the induction of galls on leaves. In such species, males are commonly smaller than females, and in some species females exhibit allometry – although competition has yet to be demonstrated amongst such species. Gall-inducing species on Acacia trees in Australia have been demonstrated to have a life-cycle in which the first generation develops into adults that are flightless and that function as soldiers to defend the gall whilst the original female continues to raise a further brood of winged adults (Crespi et al., 2004). These Acacia thrips galls are commonly invaded by kleptoparasitic thrips species. In eastern Australia there are thrips galls on many different plants, and these galls are sometimes invaded by predatory thrips species rather than kleptoparasites.
Flower-living is relatively unusual among Phlaeothripidae, although the genusHaplothrips includes a large number of species, many of which are probably host specific in the flowers of species of Asteraceae, Poaceae and Cyperaceae (Mound & Minaei, 2007). Some Phlaeothripidae are associated with mosses, and yet others are predatory on mites or on coccids (Mound, 2004). A few species have also been demonstrated to be important as pollinators on particular plants (Moog et al, 2002).
The eggs of Phlaeothripidae are deposited superficially, and the life-cycle involves two active larval stages, followed by three inactive stages, (propupa, pupa I, pupa II) before the adult emerges. Because of their unusual life cycle, Thysanoptera are sometimes referred to as the Remetabola, a sub-group of the Hemimetabola (Heming, 2003). In fungus-feeding thrips, the pupal stages occur alongside the larvae and adults, whereas among leaf-feeding species the pupal stages of some species occur at ground level.
Members of the Phlaeothripidae are highly diverse in general appearance, but are remarkably conservative in structural details.
The antennae are 8-segmented, with reduction to five segments in a very few species, and the sensoria on segments III and IV are simple emergent thin-walled trichomes. In contrast to all other Thysanoptera, the forewings have no microtrichia on the surface, there are no distinct longitudinal veins, and the marginal cilia are immersed into the wing membrane rather than arising from normal setal bases.
The last abdominal segment, segment X, is tubular with the anus at the apex and the genital opening at the base, although this tube is variously swollen in a few rare species. The ovipositor is an eversible chute-like structure.
The family Phlaeothripidae is currently interpreted as comprising about 3500 known species, these being arranged into two subfamilies. The number of genera/species recognised in these is: Phlaeothripinae 370/2800; Idolothripinae 80/700. Nomenclatural details of these taxa are available on Mound’s Thysanoptera pages.
About 45% of the genera are monobasic (ie. each one includes a single species), but in six genera more than 100 species are listed: Hoplandrothrips 105; Holothrips 125; Hoplothrips 130; Elaphrothrips 140; Haplothrips 250; Liothrips 280. The first four of these genera all involve fungus-feeding species, in which polymorphisms associated with sex, wing length, and body size confound the recognition of many species (Mound, 2005). The last of these six genera involves leaf-feeding species, many of which remain known only from single populations or even single individuals. As a result, concepts of intra-specific structural variation, and hence species identity and species diversity, amongst many genera of Phlaeothripidae are not secure.
The Phlaeothripidae is particularly species-rich in tropical and subtropical areas, and no species appears to be resident at high altitudes on mountains, nor in the subarctic and subantarctic regions. Very few Idolothripinae occur outside of the tropics and subtropics, and this is also true of the large genus Liothrips.
Available measures of the greater richness and different composition of tropical thrips faunas are:
The Phlaeothripidae is the only family recognised in the Thysanoptera suborder Tubulifera (Okajima, 2006).
The 3500 known species in this family are usually classified into two subfamilies, the Idolothripinae with 700 species in 80 genera, and the Phlaeothripinae with 2800 species in 370 genera. The Idolothripinae is probably essentially monophyletic, although it seems likely to have evolved from within the Phlaeothripinae. Two Tribes are distinguished within the Idolothripinae, but as discussed below there is no satisfactory formal classification within the Phlaeothripinae (Mound & Morris, 2007 ).
Within the Phlaeothripinae three informal “lineages” are recognised (Mound & Marullo, 1996), of which one, the Haplothripini, is now accepted as a Tribe (Mound & Minaei, 2007). The “Liothrips lineage” and the “Phlaeothrips lineage” are two very large assemblages, the first of leaf-feeding species, and the second of fungus-feeding species. There are good reasons why the classification of these insects remains unsatisfactory – many species are known to be highly variable in body form, depending on body size, sex and wing morph, but descriptions are based on a single specimen or a short series, with no allowance for intra-specific variation.
An alternative classification proposed by Bhatti (1994, 1998) involves recognition of the Tubulifera as an independent Order of Insects. This author then recognises 11 families for a total of 106 species in 28 genera, eight of these 11 families each including only a single genus. The remaining 3000 species in 400 genera are retained within the Phlaeothripidae. This emphasis on a few unusual structural features of particular genera to distinguish families contributes little to our understanding of relationships, or of how the diversity among these insects has arisen.