Placoschema
Chemsak & Hovore, 2010
Species Guides
1Placoschema is a of longhorned beetles ( Cerambycidae) in the tribe Trachyderini, established by Chemsak & Hovore in 2010. The genus contains a single , Placoschema dimorpha, which exhibits striking in coloration. The genus was described from Mexican specimens, with the first U.S. record documented from Arizona in 2013. Members are notably small and somberly colored compared to other Trachyderini, which may have contributed to their being overlooked by collectors.
Pronunciation
How to pronounce Placoschema: /plækoʊˈskiːmə/
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Identification
Placoschema can be distinguished from other Trachyderini by its small size (~10 mm), somber coloration, and sexually dimorphic elytral patterns. Males have dark with red lateral margins restricted to the basal half (in the Arizona specimen), while females have entirely reddish elytra or a darker fascia across the three-fourths. The genus lacks the bright, conspicuous coloration typical of most Trachyderini.
Habitat
The were collected from multiple localities across central and northern Mexico (Chihuahua, Durango, Hidalgo, and Mexico states). The first U.S. specimen was collected in lower Madera Canyon, Arizona, in a mesquite-acacia scrub at approximately 2 pm during hot conditions. The specific plant remains unknown, though the Arizona specimen was found near Baccharis with few flowers open at the time.
Distribution
Mexico (Chihuahua, Durango, Hidalgo, Mexico states) and the United States (southeastern Arizona, Pima County). The has a disjunct distribution with the U.S. representing a northward extension from the Mexican range.
Seasonality
activity has been documented in July in Arizona (15 July 2013 collection). The in Mexico is not well documented due to the small number of .
Human Relevance
The first U.S. record of Placoschema dimorpha represents a noteworthy range extension for a previously unknown north of Mexico. The discovery in southeastern Arizona—an area intensively collected by entomologists for decades—suggests the genus may be genuinely rare or cryptic rather than simply overlooked. The small size and subdued coloration contrast sharply with the typically large, colorful members of Trachyderini, making this genus an exceptional find for coleopterists.
Similar Taxa
- Other Trachyderini genera (e.g., Crossidius, Stenaspis)Most Trachyderini are larger and more brightly colored; Placoschema is distinguished by its small size (~10 mm) and somber coloration. The in elytral coloration is also unusual for the tribe.
More Details
Taxonomic history
The was established in 2010 by Chemsak & Hovore in Eya's revision of Trachyderini, based on just seven specimens (3 males, 4 females) from Mexico. The specific epithet 'dimorpha' refers to the pronounced in coloration.
Conservation status
The rarity of specimens in collections and the small number of known localities suggest Placoschema dimorpha may be genuinely uncommon, though this could also reflect cryptic habits or undersampling due to its atypical appearance for Trachyderini.