Leptostylus transversus | Holly Ridge Conservation Area, Stoddard Co., Missouri

The longhorned beetle subfamily Lamiinae is one of the few subfamilies in the beetle world to have its own common name—flatfaced longhorns. This photo of one of its members, Leptostylus transversus, doesn’t show the character very well, but as with all members of the subfamily the face is completely vertical, a condition called “orthognathous” (mouthparts directed downwards), while all other longhorned beetles exhibit a more prognathous (mouthparts directed forward) condition. (A third possible condition, opisthognathous, refers to mouthparts directed backwards, a condition not occurring in longhorned beetles but common in leafmining species of jewel beetles and leaf beetles.)

I beat this individual this past May from dead branches at Holly Ridge Conservation Area in Stoddard Co., Missouri. Leptostylus transversus belongs to the tribe Acanthocinini, one of the largest tribes in the family and incredibly diverse in the tropics. Most members of this tribe are colored like mottled bark, as is this one, with many also exhibiting tubercles, erect setae or tufts of setae that combine to give the beetles a rather warty appearance. I presume the combination of coloration and irregular outline contributes to their overall cryptic appearance.

When I studied the longhorned beetle fauna of Missouri (MacRae 1994), this was one of the most common species that I encountered (268 specimens from throughout Missouri were examined). Despite its abundance, two interesting features were noted for this species. Firstly, it exhibits a distinctly bimodal temporal occurrence, with most of the specimens I examined being captured either during March through June or September through October and almost none during July or August. I am not aware or many (any?) other species, at least in Missouri, that exhibit such a strongly bimodal occurrence. There are several possible explanations, such as the occurrence of two generations per year or an adult “aestivation” (summer hibernation) period, but I think it more likely that adults emerge primarily during late summer and fall, overwinter as adults, and then become active again the following spring. This latter suggestion seems to be supported by reared specimens in my collection, the great majority of which have emerged from their hosts after mid-August.

The second interesting feature of this species is its extreme polyphagy. Many longhorned beetles are quite polyphagous, but most still utilize primarily angiosperms or gymnosperms and not both. Leptostylus transversus, on the other hand, shows no preference for either group—specimens in my collection have been reared from the angiosperms Amelanchier arborea (serviceberry), Carya ovata (shagbark hickory) and Diospyros virginiana (persimmon) and the gymnosperms Juniperus virginiana (eastern red-cedar), Pinus echinata (shortleaf pine), and P. sylvestris (Scots pine). In fact, even most species that prefer gymnosperms tend to utilize either pine or juniper but not both.

REFERENCE:

MacRae, T. C. 1994. Annotated checklist of the longhorned beetles (Coleoptera: Cerambycidae and Disteniidae) known to occur in Missouri. Insecta Mundi 7(4) (1993):223–252.

Copyright © Ted C. MacRae 2013