Wednesday, May 18, 2016

Still surprises in my backyard: the Longhorn Beetle Chrotoma dunniana

This week's theme in our Facebook group SW U.S. Arthropods was the beetle family Cerambycidae. Cami Cheatham Schlappy, a  group member, looked it up: the name is derived from  Greek mythology: When the shepherd musician Cerambus  told an insulting story about nymphs, they transformed him into a large wood-chewing beetle with horns. No freedom of expression in antiquity! Our southern neighbors, more familiar with cattle than sheep, call any longhorn beetle 'el torrito', little bull.

Brothylus gemmulatus
At high elevations, Robyn Waayers, who lives among oaks and pines above Julian in California, commonly finds Brothylus gemmulatus on her patio at this time of the year. In Arizona I had to drive up to Mount Lemmon (Catalina Mountains, Pima Co. AZ) to find my first one of this species.

Achryson surinamum, a typical low desert species
In the lower desert around Tucson, AZ, the black light on our garage wall attracts the same regulars each spring.
Those Ceramcycids that suddenly show up in numbers  may have eclosed from their pupae a while ago. They then stayed in the safety of the pupal chamber until some external signal woke them up. Only then did they make the final push out of their pupal chamber.

An adult  longhorn waiting in its pupal chamber in a split log on Mt Graham
 Depending on the species these chambers are situated more or less deeply inside dead or life wood. So  this timely emergence takes some preparation. The larva usually chews an exit hole from that chamber to the outside, because the adult beetle rarely has the mouth parts to do so. This exit stays then  plugged with wood pulp until flight time.
Some twig borers instead prepare a thinned out area within the twig where it will snap off  during a strong wind (we have plenty of that this year!) and set the beetle free.

Anelaphus piceum
 This very non-distinct brown fuzzy smallish bycid is one of the first to show up each year. When I posted my first photo on FB, Steven Lingafelter said: 'I think this is what I've been getting that I'm calling Anelaphus piceum. If you turn the specimen toward you and look down the elytra from the anterior perspective, the elytral pubescence is clearly divided by a few vague, less pubescent rows along the elytral costae, and that is distinctive for this otherwise monotonous species.'
So I looked through my photos: this one clearly shows those lines in the pubescence.


Chrotoma dunniana
 Just when I thought the black light at our garage wall would not bring in any more interesting stuff after about a decade of lighting very often in that same location, a surprise appeared on a warm mid-May night. It flew not quite to the light and began scrambling over the rocks under a Palo Verde Tree. Most experts agree that this longhorn is rarely collected. The only other one on BugGuide.net are Mike Quinn's 2 Texas posts. 
Even Hovore and Giesbert wrote: A single adult of this rarely collected species was reared by us from the root crown of living snakewood, Condalia (prob. globosa var. pubescens).  Hovore, F.T. and E.F. Giesbert. 1976. Notes on the ecology and distribution of western Cerambycidae (Coleoptera). Coleopterists Bulletin, 30(4): 349-360. JSTOR
Range
CA-TX / Baja Calif., Mexico
 
Chrotoma dunniana

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