Titaenini

Belongs within: Tenebrionidae.

The Titaenini are a Gondwanan group of tenebrionid beetles in which the epipleura end well before the end of the elytra (Matthews & Bouchard 2008).

Lichen darklings

Published 29 January 2022

The beetles of the family Tenebrionidae, often referred to as the darkling beetles, are a diverse bunch. Members of this family have adapted to a wide range of lifestyles, coming in a variety of body types. Among the more obscure representatives of the tenebrionids are the members of the Southern Hemisphere tribe Titaenini.

Members of the Titaenini have a typical Gondwanan distribution, being known from southern and eastern Australia, New Zealand, New Caledonia and southern South America (Matthews & Bouchard 2008). They grow up to about a centimetre and a half in length with an elongate, parallel-sided body shape that is more or less cylindrical. The prothorax is relatively short, allowing the head to be held vertically in the Australian genus Titaena. Antennae are short with fairly simple segments not forming a club at the end. Legs have similarly simple tarsi. The tribe is distinguished from other, similar darkling beetles by the epipleura (the flattened underside of the elytral margins) which are shortened, not reaching the elytral apex. Members of the Titaenini have large repugnatorial glands opening near the end of the abdomen. In the Australian genus Titaena, at least, species are usually metallic blue or green in coloration.

The habits of the Titaenini are poorly known. As far as we do know, their larvae are specialised feeders on lichen. Adults probably pursue a similar diet. This is an exposed lifestyle, one in which you could easily come to the attention of predators, and the bright coloration of Titaena probably functions to warn off any such unwelcome interest.

Systematics of Titaenini

Characters (from Matthews & Bouchard 2008): Elongate, parallel-sided, subcylindrical or a little flattened, with fine erect setae and also adpressed and flattened white ones, head may be held vertically. Total length 3–13 mm. Edge of clypeus almost straight medially. Eyes rounded with only minor encroachment by frontal canthus. Labrum transverse, medial tormal arms of epipharynx transverse, expanded at their mesal extremities into very short anterior and posterior extensions, epitorma present, setal pattern symmetrical. Antennae short, not reaching base of prothorax, segments subtriangular, only slightly widening distally, with simple sensilla. Corpotentorium slightly arched. Mandibles apically bidentate, molar surface with fine striations. Maxilla without lacinial uncus, last palpomere securiform. Pronotum subcylindrical with fine lateral margin (rarely denticulate). Prosternum very short to moderately long before coxae. Procoxal cavities internally open.  Mesocoxal cavities partly closed by mesepimera. Metendosternite without laminae, with short stem. Elytra either with nine striae and scutellary striole, with only partial striation, or estriate with confused punctation, epipleura abbreviated, not reaching apex of elytra. Wings present, venation unmodified, with or without medial fleck, with diffuse apical flecks. Legs not fossorial, tarsomeres subparallel, plantar surfaces with sparse or moderately dense setae. Abdomen with defensive glands present, large or small, with widely separated constricted openings, without stiffening prongs, without common volume. Secretory gland cells in Titaena coalesced into a ball and emptying at bases of reservoirs via a single stem. Ovipositor with coxites and paraprocts of approximately equal length, coxite lobes 3 and 4 either fused or separate, gonostyles subapical in position and directed outwardly, baculus of coxite 1 transverse, of paraprocts longitudinal. Female tract without primary bursa, with single coiled spermatheca attached to base of accessory gland, with or without vaginal sclerite. Aedeagus with basal and apical pieces subequal in length, or basal one longer, parameres with spinules covering apical surface.

<==Titaenini
    |--Callismilax Bates 1874MB08
    |--ArtystonaB14
    |--DemtriusMB08
    |--PartystonaMB08
    |--CerodolusMB08
    |--Leaus Matthews & Lawrence 1992MB08
    |    `--*L. tasmanicus Matthews & Lawrence 1992MB08
    |--HomocyrtusB14
    |    |--H. bonniB14
    |    |--H. divesB14
    |    `--H. dromedarius (Guérin-Méneville 1831)B14
    `--Titaena Erichson 1842MB08
         |--*T. alcyonea Erichson 1842 [incl. T. ruficollis Bates 1874]MB08
         |--T. columbina Erichson 1842 [incl. T. rugosa Blanchard 1853, T. viridis Bates 1874]MB08
         |--T. minima Carter 1937MB08
         |--T. minor Carter 1913MB08
         |--T. pulchra Bates 1874MB08
         |--T. tasmanica Champion 1894MB08
         |--T. tyrrhena Carter 1913MB08
         |--T. varicolor Haag-Rutenberg 1878MB08
         `--T. wilsoni Carter 1932MB08

*Type species of generic name indicated

References

[B14] Bouchard, P. (ed.) 2014. The Book of Beetles: A lifesize guide to six hundred of nature’s gems. Ivy Press: Lewes (United Kingdom).

[MB08] Matthews, E. G., & P. Bouchard. 2008. Tenebrionid Beetles of Australia: Descriptions of tribes, keys to genera, catalogue of species. Australian Biological Resources Study: Canberra.