The Trechodini

The above figure, from Uéno (1990), shows Trechodes satoi, a fairly typical representative of the carabid ground beetle tribe Trechodini. Members of this tribe are found in many parts of the world, though they are absent from the Nearctic region and were unknown from northern Asia prior to the description of Eotrechodes larisae from the Russian Far East by Uéno et al. (1995). The greatest diversity of Trechodini is on the southern continents and most authors have accordingly assumed a Gondwanan origin for the lineage.

The Trechodini are a subgroup of the subfamily Trechinae (in the restricted sense; sometimes this grouping is reduced to a tribe in which case Trechodina is treated as a subtribe thereof). Trechines are a distinctive group of relatively small ground beetles, features of which include a head with well-developed frontal furrows extending from the front of the head to behind the eye, and two pairs of supra-orbital setae. Trechodini differ from other trechines in distinctive male genitalia in which the ejaculatory duct of the aedeagus is entirely exposed dorsally, the median lobe is open above and gutter-like, and there is no basal bulb. They also usually have three obtuse teeth near the base of the mandible though the South African genus Plocamotrechus is missing one of these teeth in the left mandible (Moore 1972).

Habitus of Canarobius oromii, from Machado (1992).

Despite being widespread, the distribution of Trechodini is patchy. They are generally restricted to damp habitats such as alongside streams and rivers. Among Australian species, Moore (1972) noted that the genera Trechodes and Paratrechodes were uniformly fully flighted whereas Trechobembix and Cyphotrechodes were often brachypterous. He suggested that this was connected to the last two genera being found in more stable habitats alongside standing water. A number of species in the tribe have moved into subterranean habitats such as caves and have reduced wings and eyes. In two genera found in lava caves on the Canary Islands, Canarobius and Spelaeovulcania, no trace of the eyes remains (Machado 1992). Considering the little-studied nature of such habitats around the world, it is possible that other trechodins remain to be discovered.
REFERENCES

Machado, A. 1992. Monografía de los Carábidos de las Islas Canarias (Insecta, Coleoptera). Instituto de Estudios Canarios: La Laguna.

Moore, B. P. 1972. A revision of the Australian Trechinae (Coleoptera: Carabidae). Australian Journal of Zoology, Supplementary Series 18: 1–61.

Uéno, S. 1990. A new Trechodes (Coleoptera, Trechinae) from near the northwestern corner of Thailand. Elytra 18 (1): 31–34.

Uéno, S., G. S. Lafer & Y. N. Sundukov. 1995. Discovery of a new trechodine (Coleoptera, Trechinae) in the Russian Far East. Elytra 23 (1): 109–117.