Sericothripinae

Mound, Laurence A. & Tree, And Desley J., 2009, Identification and host-plant associations of Australian Sericothripinae (Thysanoptera, Thripidae), Zootaxa 1983, pp. 1-22 : 2-3

Subfamily Sericothripinae

The Sericothripinae is one of four subfamilies recognised in the Thripidae , the others being the Dendrothripinae with 100 species ( Mound, 1999), the Panchaetothripinae with 130 species ( Wilson, 1975), and the Thripinae with more than 1600 species. The Sericothripinae is a group of about 140 flower and leaf-feeding, often bicoloured, species whose larvae ( Figs 54, 60, 79) have fringed or trumpet-shaped major setae ( Kudo, 1998). The adults are readily distinguished from other Thripidae by the following character states: 1. Abdominal tergites with closely spaced rows of microtrichia on the lateral thirds ( Fig. 5); 2. Abdominal dorsoventral muscles arise from small but prominent sclerotised areas laterally on antecostal ridges of tergites and sternites ( Figs 5, 53); 3. Forewing first vein with setal row complete, but second vein ( Fig. 14) usually with no setae (sometimes with one or two setae near wing apex apparently displaced from first vein). 4. All femora and tibiae with closely spaced transverse rows of microtrichia (except N. barrowi sp.n.). 5. Antennal segment VI usually with base of sensorium long and slender. Among the bicoloured species the pronotum is distinctive in having a discrete discal area, the “blotch” ( Fig. 1), the anatomical significance of which is unclear, although it appears to be internal; this structure is scarcely developed in species with a yellow body ( Fig. 52).

A total of 15 generic names have been proposed in the Sericothripinae , but ten of these were each erected for a single species, and two were erected for a few species with 7 -segmented instead of the normal 8 -segmented antennae. Most of these genera were considered synonyms by Wang (2007), but four genera are here newly treated as synonyms of Neohydatothrips , and one monobasic genus from China is here synonymised with Sericothrips . Of the three recognised genera, Sericothrips comprises nine species, eight of these being Holarctic in distribution with the ninth from South Africa. The other two genera are widespread around the world in tropical and subtropical countries, Hydatothrips with 40 species, and Neohydatothrips with 95 species. The monotypic genera now placed in synonymy were each proposed because of the presence of a particular autapomorphy, but with no consideration of relationships between the taxa involved. If this phenetic logic were applied to the Australian species, then at least two further new genera would be recognised, one for a new Hydatothrips species that seems to be unique amongst Sericothripinae in having discal setae on the posterior sternites, and one for a new species of Neohydatothrips that appears to be unique in having the ocellar setae pair III arising between the posterior ocelli. Similarly, the sub-apical wing lobe that is reported here in four species is not reported for any sericothripine species from any other part of the world, although this may be due to lack of observation.

Even the classification of Sericothripinae into the three genera accepted here is based on character states that seem unlikely to have phylogenetic significance. The nine species placed in Sericothrips are characterised by extensive microtrichial fields on the metanotum and abdominal tergites. However, each of these nine species exhibits reduction in wing length, whereas all of the species in the other two genera are always fully winged. Among Thysanoptera , as well as other groups of insects, wingless individuals commonly have modifications to their dorsal surfaces. The use of such character states to define Sericothrips suggests that this genus might be a polyphyletic assemblage of species showing wing reduction, rather than a distinct phylogenetic lineage. The other two genera are distinguished solely by the shape of the metasternum. Species with the anterior margin of this sclerite deeply emarginate are placed in Hydatothrips ; species with it only shallowly emarginate are placed in Neohydatothrips . But these differences are not always clear-cut, and the metasternum of Neohydatothrips poeta (Girault) ( Fig. 71) approaches that of some species in Hydatothrips ( Fig. 36). The validity of this distinction has been questioned previously because of the remarkable similarity between some pairs of Neotropical species currently placed one in each genus ( Mound & Marullo, 1996). The structural difference is possibly related in some way to whether a species lives predominantly on leaves or in flowers. Reduction in the number of antennal segments occurs in both genera, and the presence of a sub-apical lobe overlapping the base of the forewing terminal seta is reported here for one species of Hydatothrips and three species of Neohydatothrips . Relationships among the Sericothripinae thus need extensive re-consideration, based on species from both the eastern and western hemispheres. Segregating individual species into monobasic genera, because of the presence of some unusual structural feature, does not facilitate the ultimate objective of a generic classification, the understanding of phylogenetic relationships.