Triplax is a large genus of small beetles in the pleasing fungus beetle family Erotylidae. They are found almost anywhere where fungi grow, but seem to be less common (though still widespread) in the tropics and absent from Australasia and the Pacific region. They are placed in subfamily Tritominae, or – in taxonomic arrangements that prefer a more comprehensive subfamily Erotylinae – in tribe Tritomini of the Erotylinae.
Description Adult Triplax beetles are smallish by pleasing fungus beetle standards, a quarter-inch (6-7 mm) long at most, with the smallest individuals of the smallest species less than one-tenth of an inch in length (2.3 mm). They are usually a bit more than half as wide (1.2 to 4 mm) as they are long, and have a rather flat back. Usually pill-shaped when seen from above, with head and wingtips evenly rounded and the sides almost parallel, some species have a more tapering shape, with slightly pointed wingtips and a blunter head. From the closely related genus Tritoma, Triplax can be distinguished by a flatter and more elongated body, with narrower elytra, and shortened lines on the prosternum which do not extend forward of the attachment points of the forelegs.Goodrich, Michael A. and Springer, Charles A. (1999): The Pleasing Fungus Beetles (Coleoptera: Erotylidae) of Nebraska. Transactions of the Nebraska Academy of Sciences 25: 53-71.FulltextBoyle, Wilford Wayne (1956): A revision of the Erotylidae of America north of Mexico (Coleoptera). Bull. AMNH 110: 61-172. PDF fulltextJohnson, David H. (1967): Neotropical Species of Genus Triplax Herbst And Review of Genus Haematochiton Gorham (Coleoptera: Erotylidae). Proc. U.S. Natl. Mus. 123(3601): 1-25.
Triplax have the typical black-and-reddish colors found in many Erotylidae. Specifically, most Triplax have black elytra and a contrasting orange-yellow to reddish-blown pronotum and head. In some species, the head is also black, in others the entire pattern is reversed; some have reddish patches or bands across the elytra.
Head The head is elongate-oval and well visible from above; it has small compound eyes with tiny ommatidia, indicating a diurnal or crepuscular lifestyle, but with overall rather little reliance on eyesight. Male Triplax adults possess file-like structures at the sides of the neck attachment, which, when the beetle wiggles its head, rub against the chitin and produce a squeaking sound; these structures are developed similarly to those of, e.g., Dacne pubescens, and in Triplax species with basally margined elytra they are also present in females. The epistome has a narrow broken margin around the tip. The "cheek" lobes below the compound eyes are well-developed, and very large in some species. The length of the 11-segmented antennae is usually more than half of the pronotal base width, with antenna segment 3 always shorter than the segments 4 and 5 together, and a "clubbed" antenna tip which is at least twice as long as it is wide and not very compact.
As for the mouthparts, the galea and lacinia of the maxilla resemble those of the related genera Ischyrus, Pseudischyrus and Tritoma, the galea being almost triangular, with a tip carrying sparse bristles at the outer side and a dense pack of bristles on the inner side. The lacinia is also covered in dense bristles, and – unlike in the similar genera – at the tip has two small black incurved teeth, set so closely together that they may appear as a single tooth. The maxillary palps are more or less strongly curved inwards and have a first segment that is at least as long as segments 2 and 3 together. Their end segment is somewhat triangular, abruptly cut-off, and at least almost twice as wide as it is long; in some species its length is only 20% of its width. Its cut-off tip carries a small brush, which usually is well visible, and consists of a single row of microscopic fleshy finger-like cylinders, which on their sides have many small bristles. In some species, this brush is reduced in size, usually hidden within a slit at the palp tip, and visible only at the sides. The labium has a mentum that is fairly narrow and strongly varies from being very much reduced and triangular to being well-developed and pentagonal between species; however, even between the individuals of a Triplax species, size and shape of the mentum are somewhat variable. The labial palps end in a more or less widened hatchet-shaped segment, which is sparsely covered in short bristles, with a longer strong bristle at the outer side. At its tip, it has a tiny brush, much smaller than that at the end of the maxillary palps, and composed of a single row of short smooth nubs.
Body, wings and legs The prothorax is almost as wide at the base as the wings at their widest point and narrower at the front, giving it a trapezoidal shape. The pronotum is fairly wide and usually trapezoid-shaped, with the rear edge around half to three-quarters again as long as the forward edge, but it may be almost rectangular. A thin margin runs around the sides and rear of the pronotum, but is absent from the front between the compound eyes. In each corner of the pronotum, there is a sizeable navel-shaped pore, which may attain a conspicuously large size in some species. The prosternum may have lengthwise lines at the center margin of the leg attachments extending to the rear edge of the prosternum, but at most a tiny bit forward; more usually though, these lines are very weakly impressed or entirely missing. On the metasternum, the lines between the leg attachments are likewise absent or vestigial. The sclerites of prosternum, pronotal epipleura, mesosternum, metepisternum and metepimeres are all distinct. The abdomen consists of 5 sternites, with the first being the widest; at the abdominal base, lines between the hindleg attachments are usually present, with the tip of the abdomen protruding as a narrow bent process between the hindleg attachments.
The scutellum is bluntly pentagonal, in some species almost heart-shaped. The elytra are ornamented with regular lines of small punctuations, which may be impressed or t the same level as the rest of the elytral surface; they have a distinct margin at the base, except in those species whose females lack stridulation organs on the head. The attachments of each leg pair are set narrowly together; the fore- and mid-leg coxae are almost ball-shaped, while those of the hindlegs are wider than long. The trochanters of the hindlegs have a right triangle shape, and the femora are slightly thickened. The tibiae may be slightly widened towards the tip – depending on species, and often, but not reliably so, slightly wider in males –, and have a bluntly rounded upper/outer edge. On the 5-segmented tarsi, segment 4 is reduced, attached to the upper centerside of segment 3, and firmly joined to the base segment 5; segment 3 is straight or almost so on all sides.
Distribution and ecology Triplax beetles are almost found worldwide, except in the Australian region, but are most common in the temperate regions of the Northern Hemisphere. Almost half of the known diversity is found in Europe and west-central Asia, while just a dozen species is found in East and Southeast Asia. Roughly one-fourth of the described species occurs in Africa, and about one-fifth in the Americas (with 75% of these restricted to North America). Thus, the genus probably originated in the general Pontocaspian region.
They are woodland species, as usual for their family, and live near the shelf and tree-growing gilled fungi on which they feed. Their larval development is little-studied in detail, even though their larvae do not seem to be hard to observe, being regularly noted in passing in the literature. Active whenever the ground is not frozen, a particular preference for Pleurotus (Agaricales: Pleurotaceae) gilled and Inonotus (Hymenochaetales: Polyporaceae) shelf fungi was noted; at least in North America, most species of Triplax feed exclusively or nearly on one or the other of these fungus genera. While most pleasing fungus beetle species are not very social and tend to keep to their own kind, Triplax are noted for their gregarious habits – not rarely, dozens of adults can be found eating together on a single small mushroom. They also often occur in mixed-species groups; some, e.g. T. thoracica, habitually associate with several closely related species, suggesting some form of niche partitioning.
Species The following list includes species which 20th-century authors have usually separated in genera Paratritoma and Tritomapara, elevating Triplax to one of the larger erotylid genera, with about 100 species overall: Alvarenga, Moacyr (1994): Catálogo dos Erotylidae (Coleoptera) Neotropicais. [Catalogue of Neotropical Erotylidae (Coleoptera). Portuguese with English abstract.] Revista Brasileira de Zoologia 11(1): 1-175. .
Triplax aenea (Schaller, 1783) (= T. bicolor Marsham, 1802) Triplax affinis (Lacordaire, 1842) Triplax ainonia Lewis, 1887 Triplax akbesiana Escalera, 1925 (=T. escalerai, T. syriaca Escalera, 1925 nec Pic, 1908) Triplax alachuae Boyle, 1956 Triplax alvarengai Johnson, 1967 Triplax amoena Solsky, 1871 Triplax analis Reitter, 1892 Triplax andreinii Pic, 1930 Triplax apicipennis Reitter, 1901 Triplax atricaudata (Kuhnt, 1910) Triplax atripennis Iablokoff-Khnzorian, 1975 Triplax atroguttata (Araki, 1943) Triplax bedeli Reitter, 1888 Triplax bicolorata (Chûjô, 1941) Triplax brasiliensis (Guérin, 1946) Triplax breviscutata Fairmaire, 1868 Triplax bruchi (Kuhnt, 1910) Triplax bussleri Triplax caduca (Gorham, 1888) Triplax californica LeConte, 1854 (= T. antica) Triplax canalicollis Lewis, 1887 Triplax carpathica Reitter, 1890 Triplax castanea Peyerimhoff, 1925 Triplax caucasica Reitter, 1892 Triplax collaris (Schaller, 1783) (= T. capistrata, T.sulphuricollis) Triplax contienensis Alekseev, 2014 Triplax cuneata Boyle, 1954 Triplax cyanescens Bedel, 1868 (= T. melanocephala Lacordaire, 1842, nec Latreille, 1804) Triplax cyanipennis Motschulsky, 1858 Triplax devia Lewis, 1887 Triplax dimidiata (Gorham, 1888) Triplax discicollis Lewis, 1887 Triplax dissimulator (Crotch, 1873) Triplax divisa (Gorham, 1888) Triplax elongata Lacordaire, 1842 Triplax elongatoides Mader, 1941 Triplax emgei Reitter, 1885 Triplax errans Boyle, 1956 Triplax festiva Lacordaire, 1842 (= T. fasciata) Triplax flavicollis Lacordaire, 1842 (= T.championi, T.confinis, T.hogei, T.mesomelas) Triplax flaviventris Tôyama, 1986 Triplax frontalis Horn, 1862 – black-fronted triplax (= T.occipitalis) Triplax frosti Casey, 1924 Triplax fukudai (Chûjô, 1941) Triplax gracilenta Solsky, 1871 (= T. bicoloripes) Triplax horni (Chûjô, 1941) Triplax hurusyoi (Chûjô, 1941) Triplax japonica Crotch, 1873 Triplax lacensis Boyle, 1954 Triplax lacordairii Crotch, 1870 (= T. bicolor Stephens, 1830, nec Marsham, 1802, T. ragusae, T. ruficollis Lacordaire, 1842, nec Stephens, 1830, T. rufoapicalis) Triplax latipalpus Johnson, 1967 Triplax lepida (Faldermann, 1837) Triplax lugubris Motschulsky, 1858 Triplax macclurei Chûjô, 1963 Triplax macra LeConte, 1854 Triplax marcescens Boyle, 1954 Triplax marseuli Bedel, 1868 (= T. discicollis Reitter, 1904, nec Lewis, 1887, T. reitteri) Triplax meghriensis Iablokoff-Khnzorian, 1978 Triplax melanocephala (Latreille, 1804) (= T. collaris (Fabricius, 1801) nec Schaller, 1783, T. nigriceps, T. ruficollis Stephens, 1830) Triplax melanoderes (Kuhnt, 1910) Triplax menetriesi Faldermann, 1837 Triplax mesosternalis Schaeffer, 1905 (= T.coloradana, T. monostigma) Triplax microgaster Boyle, 1954 Triplax nagaoi Nakane, 1977 Triplax nakanei (Chûjô, 1941) Triplax nigrina Reitter, 1879 Triplax nigritarsis Reitter, 1898 Triplax paganetti Obenberger, 1914 Triplax peyerimhoffi Escalera, 1925 Triplax pseuda Heller, 1920 Triplax punctatipennis Heller, 1918 (1920) Triplax puncticeps Casey, 1916 Triplax pygmaea Kraatz, 1872