On a recent collecting trip, I went over to Chalk Bluffs Natural Area in the Mississippi Alluvial Plain of northeastern Arkansas. My quarry was a population of Cylindera cursitans (ant-like tiger beetle) that has been reported from the site—one of the only known sites for the species in Arkansas. While I was there, I noticed some movement on the trunk of a tree, and a closer look revealed that what appeared to be a piece of bark was actually a beetle—a longhorned beetle to be precise. The elevated gibbosities of the pronotum and white, transverse fasciae of the elytra immediately identify it as Acanthoderes quadrigibba, a not uncommon species in the eastern U.S., but one that I still get excited about whenever I encounter it.
Judging by the number and diversity of plant genera that have been recorded as larval hosts for this species—Linsley and Chemsak (1984) recorded Acer, Betula, Carya, Castanea, Celtis, Cercis, Fagus, Ficus, Quercus, Salix, Tilia, and Ulmus—you could be forgiven for thinking that this is one of the most common and abundant species of longhorned beetle in North America. I have not found this to be the case, and I don’t think it is because I’m simply missing it due to its cryptic appearance. Longhorned beetles in the tribe Acanthoderini are, like many species in the family, quite attracted to lights at night, and I’ve done plenty of lighting over the years. What I have noticed is that nearly all of my encounters with this species have been in the Mississippi Alluvial Plain—an area rich with wet, bottomland forests that contrast markedly from the dry to dry-mesic upland forests that cover much of the southern two-thirds of Missouri. I’ve also reared the species a few times from Salix, one of the host genera recorded by Linsley and Chemsak (1984). In both cases, the wood was not freshly dead (as is commonly preferred by many other longhorned beetles), but a little past its prime and starting to get somewhat moist and punky. In the case of this beetle, I suspect that the nature of the host wood may be more important than the species, the preference being for longer dead wood in moister environments. Of course, observations by another collector in another state may completely obliterate my idea, but for now it sounds good.
A closeup photograph of the elytral markings of this beetle was the subject of ID Challenge #9, to which a record 18 participants responded (thanks to all who played!). Troy Bartlett takes the win with 12 points (and attention to detail), while Dennis Haines, Max Barclay, Mr. Phidippus, and Josh Basham all score double-digit points. Troy’s win moves him into the top spot in the overall standings of the current BitB Challenge Session with 23 pts, but Dave is breathing down his neck with a deficit of just a single point. Tim Eisele and Max Barclay have also moved to within easy striking distance with 19 and 18 points, respectively, and several others could make a surprise move if the leaders falter. I think I’ll have one more challenge in the current session before deciding the overall winner—look for it in the near future.
Linsley, E. G. and J. A. Chemsak. 1984. The Cerambycidae of North America, Part VII, No. 1: Taxonomy and classification of the subfamily Lamiinae, tribes Parmenini through Acanthoderini. University of California Publications in Entomology 102:1–258.
Copyright © Ted C. MacRae 2011