Placoschema dimorpha

The combination of extremely small size (~10 mm) for Trachyderini, somber black and red coloration, and sexual dimorphism in elytral pattern distinguishes this species from other North American trachyderines. Males can be recognized by black elytra with red lateral margins on the basal half; females by uniformly reddish elytra. The only member of the genus Placoschema, so no congeners occur in the region. Similar small cerambycids in Arizona include other Trachyderini, but these are typically larger and more brightly colored.

Collected in lower Madera Canyon, Arizona in mesquite/acacia scrub and oak/juniper woodland at approximately 1400 m elevation. The type locality in Mexico and U.S. collection site suggest association with riparian or canyon-bottom habitats in the Madrean sky island region.

Mexico: described from specimens collected across central and northern Mexico in the states of Chihuahua, Durango, Hidalgo, and Mexico. United States: first documented from Pima County, Arizona (lower Madera Canyon) in July 2013, representing a northward range extension of approximately 500 km from the nearest Mexican records.

Adults have been collected in July. The single U.S. record is from 15 July 2013.

• Baccharis - adult feedingAdults searched on Baccharis, though few flowers were open at time of collection; specific host plant of collected specimen unknown
• Quercus hypoleucoides - probable larval hostInferred from tribe-level biology; one specimen photographed on burned pine tree but oak suspected as true host based on Trachyderini biology

Adults have been observed active during midday heat (collected at ~2 pm). The U.S. specimen was collected by roadside sweeping, suggesting adults may be found on vegetation near roadsides in suitable habitat.

Of interest to coleopterists as a rare, recently described species with a remarkable range extension into the well-collected region of southeastern Arizona. The 2013 U.S. discovery highlights that even in heavily scrutinized areas, small, inconspicuous species can remain undetected.

• Crossidius spp.Sympatric trachyderines in Arizona, but these are larger, more brightly colored, and associated with rabbitbrush (Ericameria, Chrysothamnus) rather than the habitat where P. dimorpha was found.
• Other TrachyderiniMost North American trachyderines are substantially larger (typically 15-30+ mm) and exhibit more vivid color patterns of red, orange, or yellow with black markings.

• longhorned beetle
• Cerambycidae
• Trachyderini
• sexual dimorphism
• range extension
• Madrean
• sky islands
• rare
• recently described

• BugGuide
• GBIF taxonomy match
• Catalogue of Life
• taxonomy | Beetles In The Bush | Page 5
• Cerambycidae | Beetles In The Bush | Page 9
• Belostomatidae | Beetles In The Bush