Tritoma

Tritoma is a large genus of beetles in the family Erotylidae, the pleasing fungus beetles. It is distributed mainly in the temperate parts of Eurasia, with a large evolutionary radiation in Japan. They are less diverse in North America (where a mere handful of species occur in the east) and the tropics (where records are scarce except for the abundant Tritoma dorsalis of Central America). Among its family, this genus is placed in subfamily Tritominae, or – in taxonomic arrangements that prefer a more comprehensive subfamily Erotylinae – in tribe Tritomini of the Erotylinae. As of 1999, over 100 species were recognized.^[2][3][4]

Some species consume euagaric mushrooms, staying concealed amidst the gills as they feed.^[5] Some feed on mushrooms growing from dead trees, as well as mycorrhizae on living roots.^[6] One of the most common pleasing fungus beetles in Europe, T.bipustulata, is a black beetle with red spots which engages in autohaemorrhaging as a defensive behavior.^[7]

Molecular analysis suggests that Tritoma in its traditional circumscription is paraphyletic, and even the few North American species seem to represent at least two well-distinct genera: The lineage containing the uniformly dark-winged T.erythrocephala and T.unicolor appears to be far more closely related to the iridescent Spondotriplax antennalis from New Guinea than to T.pulchra with bicolored wings; the latter appears as sister to an unidentified species which resembles a member of the Neotropical genus Mycotretus but does not seem to be closely related to Mycotretus scitulus.^[5]

However, the only established synonym of genus Tritoma, Cyrtotriplax, is not available to use for a split-off genus. It was proposed by George Crotch in 1873 to replace Tritoma. That name had been first used in Étienne Geoffroy's 1762 Histoire abrégée des Insectes for the genus commonly called Mycetophagus from the late 18th century onwards – these are hairy fungus beetles, superficially similar but not particularly closely related to the pleasing fungus beetles described as Tritoma by Johan Fabricius in 1775. This mix-up caused considerable misunderstanding among coleopterologists throughout the 19th and 20th century, until the ICZN in 1994 fixed Fabricius' publication as the official establishment of the genus and invalidated Geoffroy's description, conserving the use of Tritoma for the pleasing fungus beetle and Mycetophagus for the hairy fungus beetle. Cyrtotriplax, which used T.bipustulata as its type species just like Fabricius' Tritoma does, thus became an objective synonym, and unavailable for any split-off genera.^[1]

Data sources: g = GBIF,^[3] b = Bugguide.net,^[2] w = Wikispecies

In addition, a fossil Erotylidae beetle described originally as Mycotretus binotata by Samuel Scudder in 1878 has been assigned to Tritoma due to its great resemblance to T.sanguinipennis. Its specimen MCZ 4183 was found in the Lake Gosiute Green River Formation of Wyoming and originally assumed to be of Oligocene age; today, it is assumed to have been lived somewhat later, in the Early Eocene roughly 50 million years ago.^[9]