External relationships and phylogeny
Systematics
Within the Condylognatha Thysanoptera is classified as a sister group of Hemiptera (true bugs). In these insects maxillae and mandibles have become stylets. Therefore Condyloghnata is considered monophyletic. The Thysanoptera’s genesis – with the asymmetric and asynchronous action of their mouthparts – is presumably based on an adaptation to specialized food: pollen. Pollen grains are so small (20 – 40µm), that the use of more than one single stylet would squash, rather than puncture, the tough wall. That explains why, to the ancestors of modern Thysanoptera trying to feed on pollen grains, two mandibles were an evolutionary disadvantage, and the atrophy of one has enabled thrips to exploit this rich source of food. The transference to feeding on plant juices is probably a later development, and fungus-feeding an even more modern adaptation. (Lewis, T. 1973: Thrips: their biology, ecology and economic importance. Academic Press, London & New York).
Thysanoptera once have developed from Lophioneurida. If this extict order is included, both Thysanoptera and Lophioneurida are classified into the superorder Thripida. For more details, see Evolution.
The internal relations of thrips have been little studied. Currently, most entomologists classify Thysanoptera into nine extant families, grouped within two suborders, Terebrantia and Tubulifera. The specific phylogenetic relations between these families, however, remain uncertain. Phenetic features of the relevant taxa are equivocal, particularly, concerning the relation of the Phlaeothripidae towards other families.
Within their suborders Thysanoptera includes the following families (†: families including fossil taxa only; links show one species as an example):
Terebrantia: Aeolothripidae, Fauriellidae, † Hemithripidae, Heterothripidae, † Karataothripidae, † Liassothripidae, Melanthripidae, Merothripidae, Stenurothripidae, Thripidae, † Triassothripidae, Uzelothripidae
Tubulifera: Phlaeothripidae, † Rohrthripidae
Studies using molecular biology techniques indicate the subfamily Panchaetothripinae, which is currently associated with the Thripidae, as an autonomous family, that presumably was separated very early. Future modern techniques, definitely, will influence and restructure our view on the internal relations of Thysanoptera.