Trichadenotecnum: Six Spots and Spiny Terminalia

Trichadenotecnum sexpunctatum, photographed by Brian Valentine.

The animal in the photo above is a typical representative of Trichadenotecnum, a diverse genus of the barklice. About 200 species have been assigned to this genus from almost all the major biogeographic regions of the world except Australia (Yoshizawa et al. 2007); of the two species recorded from Australia and assigned to this genus, one (Ptycta enderleini) has recently been excluded from Trichadenotecnum, and the other (Trichadenotecnum circularoides) is probably a recent introduction from the Americas (Yoshizawa & Smithers 2006). Though long regarded as suspectly heterogenous, the genus has been extensively reviewed in recent years, particularly by Kazunori Yoshizawa of Hokkaido University and associates (Yoshizawa 2001, 2004; Yoshizawa et al. 2008). Members of Trichadenotecnum are characterised by a distinctive array of wing markings, visible in the above photo. Note, in particular, the series of six submarginal spots forming a U-shape towards the end of each wing (though, confusingly, these characteristic markings can become difficult to distinguish in species in which the wings are more heavily spotted overall). The genus is also distinguished by certain features of the male terminalia (or, in layman's terms, the bum) with a number of processes developed on the hypandrium, the posteriormost segment of the underside of the abdomen that covers the phallosome, the intromittent organ in Psocoptera. These processes vary in development between species, and often themselves bear arrays of small spines or teeth. A number of species of Trichadenotecnum also have the terminalia assymmetrically developed, with the left and right lobes of the hypandrium (for instance) differently sized and/or shaped, though the functional significance of this arrangement (if any) remains unknown.

Various views of the terminalia of Trichadenotecnum alexanderae, from Yoshizawa (2001). In life, the phallosome is contained within the underside of the terminalia.

The variability of the terminalia between species of Trichadenotecnum makes them a rich source of characters for use in taxonomy. The problem with this, of course, is that you need adult males, and that isn't always easy. Particularly in a group like Psocoptera, which seem to show a particular tendency for parthenogenesis. A number of Trichadenotecnum species are not, as yet, known to produce males, including the aforementioned T. circularoides, necessitating identifiers to fall back largely on wing markings. Trichadenotecnum circularoides has been recorded from Angola, east Asia, Australia, North America and Brazil; the distribution of closely related species suggests that the last locality represents its original homeland with human dispersal carrying it elsewhere (Yoshizawa et al. 2008). The New World species of Trichadenotecnum appear to fall within a small number of clades: one including T. circularoides is the sister group to other members of the genus, while the T. alexanderae species group is Holarctic in distribution. The majority of New World species, however, form a single lineage referred to as the 'bulky clade' by Yoshizawa et al. (2008). Members of the bulky clade have a movable median tongue on the hypandrium that bears a dorsal covering of denticles or spines. Yoshizawa et al. (2008) suggested that, as the bulky clade was nested amongst a number of Old World lineages, this group may represent a relatively recent invasion of the Americas, probably by way of the Bering Strait.

Nymphs of Trichadenotecnum possess glandular hairs to which frass and pieces of lichen become attached, providing them with camouflage. This individual was photographed by Charley Eiseman.
REFERENCES

Yoshizawa, K. 2001. A systematic revision of Japanese Trichadenotecnum Enderlein (Psocodea: ‘Psocoptera’: Psocidae: Ptyctini), with redefinition and subdivision of the genus. Invertebrate Taxonomy 15: 159-204.

Yoshizawa, K. 2004. Molecular phylogeny of major lineages of Trichadenotecnum and a review of diagnostic morphological characters (Psocoptera: Psocidae). Systematic Entomology 29: 383-394.

Yoshizawa, K., A. N. García Aldrete & E. L. Mockford. 2008. Systematics and biogeography of the New World species of Trichadenotecnum Enderlein (Insecta: Psocodea: ‘Psocoptera’: Psocidae). Zoological Journal of the Linnean Society 153: 651-723.

Yoshizawa, K., C. Lienhard & V. K. Thapa. 2007. Systematic study of the genus Trichadenotecnum in Nepal. Insecta Matsumurana, new series 63: 1-33.

Yoshizawa, K., & C. N. Smithers. 2006. Systematic position of Trichadenotecnum enderleini (Roesler) (Psocodea: “Psocoptera”: Psocidae). Records of the Australian Museum 58: 411-415.