Tritoma angulata

Tritoma angulata is a species of small pleasing fungus beetle (family Erotylidae) endemic to the USA. It belongs to subfamily Tritominae, or – in taxonomic arrangements that prefer a more comprehensive subfamily Erotylinae – in tribe Tritomini of the Erotylinae.

Tritoma angulata
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Clade:	Pancrustacea
Class:	Insecta
Order:	Coleoptera
Suborder:	Polyphaga
Infraorder:	Cucujiformia
Family:	Erotylidae
Genus:	Tritoma
Species:	T. angulata
Binomial name
Tritoma angulata Say, 1826

Description

This is a tiny beetle, widely oval in shape with somewhat pointed wingtips, and about 2.6 to 4.35 mm long as adults; unlike most Tritoma, they lack contrasting red coloration on the elytra and/or pronotum. The adults are almost entirely blackish, with a browner underside and head, and yellow-orange legs whose tibiae are conspicuously widened. As typical for Tritoma sensu stricto, T.humeralis also has a triangular mentum, as well as an epistome whose tip is sharply cut off, causing the line running parallel to the epistome margin to angle towards the antennae insertions.

From its close relative T.unicolor, apart from the leg color it can also be distinguished by having punctures on the pronotum which are very uniformly sized and spaced, and conspicuously widened tibia tips. Another highly similar (but more distantly related) pleasing fungus beetle found across the southern part of the range of T.angulata is Pseudischyrus extricatus, which differs in the structure of the genitalia, and – visible with a powerful magnifying glass without harming the beetle – the few and large ommatidia of its compound eyes, which are smaller and more numerous in T.angulata. This difference is also relevant because it indicates that T.angulata is diurnal or crepuscular, while P.extricatus is decidedly nocturnal.

Range and ecology

T.angulata is found in the eastern to central USA, from the New England states to Michigan, Missouri, Iowa and Nebraska in the north, and from Florida to Arkansas and Texas in the south. There is also a single specimen whose collection locality is given as "Pasadena, Cal.", but this is probably erroneous. Records from the western limit of its range, e.g. Iowa and Nebraska, are scarce, but this beetle is usually under-recorded, being less prone to getting into Malaise traps than other Tritoma species. To thrive, this species seems to require higher temperatures than many of its relatives: in Illinois and Missouri, for example, sizeable numbers of adults are noted only between June and early September.

This beetle, like its closest relatives, eats gilled fungi as larva and adults. Its main food source seems to be fungi of the "brittlegill" family Russulaceae in order Russulales. Among these, the blancaccio (Lactifluus piperatus) has been found most often in association with T.angulata and is also suitable as larval food, as is the related Lactifluus subvellereus which seems to be somewhat less popular with this beetle. But many records of T.angulata larvae exist from unidentified Russulaceae; probably, many members of the family are suitable as food for this beetle's adults, and several might even feed its more demanding larvae.

For adult T.angulata, the green brittlegill (Russula aeruginea) as well as R.mariae and R.subalbida also seem to be quite attractive, but somewhat less so than the two Lactiflua. Additional records of adult T.angulata are from species such as the weeping milkcap (Lactifluus volemus), Lactarius argillaceifolius, the birch milkcap (Lactarius tabidus), Lactarius zonarius, the boring white russula (Russula albidula), R.compacta, the crusty russula (R.crustosa), the emetic russula (R.emetica) or a related species, the stinking russula (R.foetens), R.paludosa, and the shrimp russula (R.xerampelina). Such rare records, like the occasional reports of T.angulata from non-Russulaceae fungi such as the ringless honey mushroom (Desarmillaria tabescens) of family Physalacriaceae in order Agaricales, do not necessarily imply that the beetles were actually feeding on those fungus species rather than simply sheltering there, or that the fungus in question was even correctly identified; at any rate, none of these species seems to be suitable as larval food. However, the larva of T.angulata and their development are still little-studied.