Placoschema dimorpha (male) | lower Madera Canyon, Arizona

If you are a collector of beetles in Arizona, you should be on the lookout for longhorned beetles (family Cerambycidae) resembling the specimen in the above photos. Determined as Placoschema dimorpha Chemsak & Hovore, in Eya 2010 by Jeff Huether, the specimen was collected by Jeff’s son Mark Huether on 15 July 2013 as they roadside collected longhorned beetles and scarabs in lower Madera Canyon (Pima Co.). They were searching mainly on Baccharis, although there were very few flowers open at the time. It is not known what plant the specimen was collected from, but Jeff notes that it was collected around 2 pm in the heat of the day.

Placoschema dimorpha was described from just a handful of specimens (3 males and 4 females), all in Mexico, and is the only member of the genus. As a result, the above collection represents the first record of both the genus and the species in the U.S. New U.S. records for popularly collected groups like longhorned beetles are always noteworthy, and in this case its occurrence in southeast Arizona—well scrutinized for decades by legions of beetle collectors—is all the more remarkable. Perhaps its tiny size (the above specimen measures only ~10 mm) and somber coloration—unusual for the tribe Trachyderini with its mostly large and colorful members—have somehow contributed to it being overlooked until now. Others might be quick to cite climate change and recent expansion of its range northward into the U.S. as a possible explanation; however, it should be noted that the type specimens, despite being few in number, were collected from a rather large area across central and northern Mexico in the states of Chihuahua, Durango, Hidalgo, and Mexico.

While this specimen agrees very well with the original description of P. dimorpha, it does differ from the male paratype figured in that work in that the lateral margins of the elytra are red only in the basal half rather than completely to the apex. As the species name implies, females are colored differently, with the elytra entirely reddish or at most a darker fascia (may be incomplete) across the apical three-fourths.

My sincere thanks to Jeffrey Huether for allowing me to photograph this specimen and present these notes in advance of more formal documentation in peer-reviewed literature.

REFERENCE:

Eya, B. K. 2010. New Mexican and Central American genera and species of Trachyderini (Coleoptera, Cerambycidae, Cerambycinae). Les cahiers Magellanes 108:1–21.

Copyright © Ted C. MacRae 2013