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Discoderus impotens (LeConte) - Discoderus impotens

Discoderus impotens (LeConte) - Discoderus impotens
nr Double Adobe, 1219 m, Cochise County, Arizona, USA
September 2, 1979
det. R. Davidson
at light
specimen curated at UAIC

Wonder if image really supports "Discoderus impotens"
as Casey (1914) distinguishes this species from others by its strongly transverse pronotum as clearly shown by the images of the type specimen. See the close-up view of the pronotum. Atop my display screen here I measured the ratio of pronotal width:pronotal length to be ~ 1.28, short of the ~ 1.4 or greater expected for D. impotens. The pronotal outline should have a more "rectangular" feel (with subparallel sides) in the latter species. Of course expert Robert Davidson would have the final word since he actually examined this specimen. I find the keys by Casey for Discoderus to be confusing and likely fraught with many synonyms. This group is in desperate need of a modern revision.

Desperately seeking "Discoderus impotens"!
One unique constant for D. impotens that I now suspect (via literature + examination of 2 specimens) is that the pronotum has a subtle bisinuate basal margin. The image posted here is too distant to see details of the basal margin. From the specimens I've inspected, the pronotum should be visibly narrower in D. impotens. The images shows the pronotum about as wide as the elytra. Currently I'm lacking comparative material of Discoderus to say much more with confidence.

Our knowledge about Discoderus species separation is still very tenuous, remains opinionated, and is bound to change significantly if ever a serious revision of the genus hits the literature. In the meantime we carabidologists reserve the right to change our previous species determinations without criticism from peers with each new flash of insight that comes along.

Moved from Ground Beetles.

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