Mycotretus

Mycotretus is a genus in the pleasing fungus beetle family (Erotylidae). They are small, oval beetles, and often very colorful and boldly patterned in yellowish, orange-red to chestnut-brown, and black hues; historically, they were popular with insect collectors. 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.^[1][2]

These beetles are found throughout the Neotropics except on high mountain ranges. Some isolated records from temperate North America presumably refer to introduced specimens. One species (M.nigromanicatus) ranges as far north as the Chiricahua Mountains of Arizona, USA, while in the south of the genus' range, several species are found in Paraguay and northern Argentina. While some species, such as M.ornatus, M.pygmaeus and M.scitulus, occur almost across the entire range of the genus, many are restricted to a single range of hills or to one area bordered by large rivers, with Mexico and the Amazon Basin having the highest diversity of Mycotretus.^[3][4]

This genus has a convoluted nomenclatural history involving the related genera Ischyrus and Lybas;^[5] in addition, its delimitation against Mycomystes was long disputed and as of 2023 is still not fully resolved.^[2]

Mycotretus is one of the largest genera in this family – possibly the second-largest; after its latest revision in 2023, when numerous supposed species were synonymized with others (in particular the highly variable Mycotretus ornatus) or moved to other genera, it still contained almost 170 accepted species.^[2]

The genus names Ischyrus, Lybas and Mycotretus were first published by Pierre Dejean in the second edition of his Catalogue des Coléoptères in 1836^[6]; however, he attributed these names to Louis Chevrolat instead of claiming authorship himself. Dejean's catalog was a simple list of names, with no diagostic criteria or descriptions, but as he included well-known species that hat been extensively described by previous authors in each of his genera, his genera are technically valid.^[5]

Jean Lacordaire in 1842 published a monograph on the pleasing fungus beetles. Therein, he also used the genus names Ischyrus, Lybas and Mycotretus, attributing them to Chevrolat just as Dejean did. However, Lacordaire placed Dejean's Lybas species in Mycotretus and re-established the genus Lybas for Lybas normalis, a species mentioned by preceding authors such as Dejean, but never validly described until Lacordaire's 1842 work. Meanwhile, most of Dejean's small Mycotretus species were moved into Ischyrus by Lacordaire, where they formed a second "division" (subgenus) distinct from the large tropical species which had already been placed in Ischyrus by Dejean.^[5]

In 1873, George Crotch split genus Ischyrus, elevating Lacordaire's groups to full genus status. But he retained the name Ischyrus for the second group, which had been treated as Mycotretus by Dejean. The first group, Dejean's Ischyrus, was named Megischyrus by Crotch. For his remaining Ischyrus, Crotch designated Olivier's Erotylus quadripunctatus as type species. As he only referred back to Lacordaire, Crotch overlooked that Dejean had included this species in Mycotretus, preventing its use as type species of Ischyrus.^[5]

However, Crotch failed to designate a type species for Mycotretus. W.W.Boyle attempted to correct this in 1956, and selected the beetle described as Erotylus leseuri by Chevrolat in 1935. But like Crotch with his Ischyrus type species, Boyle did not note that Dejean had included this species in his genus Lybas at the time when he established Mycotretus, making Boyle's type designation invalid.^[5]

Subsequent authors applied the genus names as proposed by Crotch and Boyle, until Moacyr Alvarenga in 1965 revalidated Dejean's Ischyrus with E.undatus as type species, making Megischyrus a junior objective synonym and invalidating it. For the second group, containing most of Dejean's Mycotretus, Alvarenga established the genus Micrischyrus, with E.quadripunctatus as type species to exactly replace Crotch's Ischyrus which had become a junior homonym by the abolishment of Megischyrus, and likewise invalidated. However, almost all Erotylidae research at that time was published in English, with Japanese and German having some minor relevance due to prolific experts Michio Chûjô and Kurt Delkeskamp, whereas Alvarenga published in Brazilian Portuguese and his nomenclatural acts appeared in the then little-known zoological bulletin of the Federal University of Paraná (now Acta Biologica Paranaense). Consequently, unaware of Alvarenga's proposed solution to a problem they often were not even aware of in the first place, other erotylid researchers continued to apply Crotch's nomenclature. As for Mycotretus, its authorship was mistakenly referred by Alvarenga to Chevrolat, 1837, with M.ornatus (under its original name Erotylus ornatus) as alleged type species.^[5]

To resolve this situation, Paul E. Skelley and Michael A. Goodrich in 1994 petitioned the ICZN to rule Dejean's descriptions as invalid; this would preserve the prevailing genus assignments. In 1996, the ICZN agred to this proposal, establishing Lacordaire as the author of Mycotretus due to Crotch's and Boyle's revalidation of his genus. This also permitted E.leseuri to be type species of Mycotretus, courtesy of Lacordaire having moved it there.^[7]

In addition, the names "Mycotretus bruchi" and "M.unguicularis", despite having been attributed to Bruch, 1915, were never validly established; they are nomina nuda. The former has been identified as Mycotretus trifasciatus, while the latter is still undeterminable.^[2]

In the 2023 revision, several species traditionally placed in Mycotretus turned out to belong to other genera:^[2]

• "Mycotretus" apicalis (including M.coccinelloides, M.corallipennis, M.gemmula, M.gentilis, M.nigroterminatus and M.pulicarius), "Mycotretus" coccineus (including M.sanguinosus and M.unicolor), "Mycotretus" fuscitarsis, "Mycotretus" melanophthalmus (including M.cinctellus and M.discoidalis) and "Mycotretus" peruvianus are now in Mycomystes
• "Mycotretus" antesignatus is now in Mycolybas
• "Mycotretus" fasciatus belongs to genus Epopterus of family Endomychidae (handsome fungus beetles)
• "Mycotretus" virgatus is now in Iphiclus