Phlaeothripidae: Idolothripinae

Recognition

Adults and larvae of Idolothripinae have the maxillary stylets broad, that is, the width of these stylets in their distal half is between 5 and 15 microns in diameter. It is essential to distinguish between the "maxillary stylets" and the closely associated "maxillary guides" when attempting to distinguish between members of the idolothripinae and members of the Phlaeothripinae. In some phlaeothripine species, the maxillary guides are much more robust in appearance than the stylets, with the result that the stylets are easily overlooked and the maxillary guides misinterpreted as stylets. The width of the stylets must be estimated in their distal half, because the bases of all maxillary stylets are equally stout. If the maxillary stylets have become dissociated and moved during slide-preparation, they are then particularly difficult to interpret. The other differences between members of the two subfamilies do not fully discriminate between these two groups. Males of Idolothripinae never have a pore plate on sternite VIII, and they never have setae S2 on tergite IX shorter and stouter than setae S1, whereas one or both of these character states is often (but not always) present in males of Phlaeothripinae.

Classification

Although the Idolothripinae is possibly monophyletic, it is not likely to be sister-group to the Phlaeothripinae (Mound & Morris, 2007). Two Tribes are currently recognised within the subfamily, the Pygothripini with six sub-tribes (Pygothripina, Allothripina, Compsothripina, Gastrothripina, Diceratothripina, Macrothripina), and the Idolothripini with three (Elaphrothripina, Idolothripina, Hystricothripina) (Mound & Palmer, 1983). Although the position of a few small genera remains equivocal, including Dermothrips and Hartwigia, this classification appears to be stable.

Diversity

The species placed in Idolothripinae range from the largest of Thysanoptera to some of the smallest, and from jet black, fully winged individuals to pale yellow, wingless adults. Many species appear to be sub-social with behaviour that involves male fighting, judging from the patterns of structural variation among males. Other species are monomorphic. Allometry is common in species with variably-sized males, and large males of a species may have unusual structures, such as horns on the thorax, that are not developed in small males. Many of the smaller species in the subfamily that live at ground level have the habit of lifting the tip of the abdomen over the head, such as Nesothrips propinquus; in such species the sternites are longer than the tergites, and in some species the tube is broadly conical, as in Pygothrips species.

Biology

Members of this subfamily are presumed to all feed on fungal spores. For many species this is very evident, because the gut content commonly involves a black bolus of undigested spore walls. However, clear evidence of spore-feeding is not available for all species. These thrips are found in leaf litter, on dead branches, and on dead hanging leaves, and the species on dead branches and in bunches of dead leaves sometimes produce colonies of hundreds of individuals. Some genera are associated primarily with fungi at the bases of tussocks of grasses and reeds, such as Bolothrips and Compsothrips species, the latter being remarkable ant-mimics both in appearance and behaviour. Idolothripinae appear to be associated primarily with the early stages of fungal decay, and only a few species are known from rotting wood, including Ecacleistothrips glorious that was taken in Australian rain forest in association with the black fungus Xylaria. Idolothripinae are most diverse in tropical areas, particularly the wet tropics, and only a few species occur in temperate parts of the world, and very few in arid areas. Some of the larger species exhibit sub-social behaviour, with males competing with each other to protect particular egg-masses, and ovoviviparity occurs in some species.

Idolothripinae Keys

Subfamilies A-Z