Carabidae - Stenolophus lecontei

We gave up

Even with the beetles in front of us, we couldn't separate them. Some were clearly comma and some were clearly lecontei. But most of them...???

… john and jane balaban, 1 November, 2013 - 11:11pm

Moved

Moved from subgenus Tachistodes. Sorry V, we led you astray with the size - and we even took its picture with a scale, and still messed it up!
We can see the difference between the pronotum edge in our two images, but we're struggling as we look through the guide at the dark markings. Seems like this one would be lecontei?

… john and jane balaban, 31 October, 2013 - 11:14pm

No, you were right!

We photographed several next to the scale. One with its head down looks to be a little over 5mm but one stretched out flat is closer to 6mm. We'll post the images tomorrow. Thanks for sending us back to the specimens. Is there something that we can look at to separate comma from leconte (besides reproductive parts)? We just didn't see a difference except size.

… john and jane balaban, 30 October, 2013 - 9:46pm

Stenolophus comma vs S. lecontei

Stenolophus comma vs S. lecontei after text and figures in "Illustrated Identification Guide" by Bousquet (2010).

Elytral interval #1 as pale as background colour of elytron; dark macula of elytron not extended anteriorly on interval 2 compared to intervals 3 and 4 (Fig. 308). Scutellar stria proportionately long. Pronotum (Fig. 306) with side not sinuate in front of posterior angle which is well rounded; posteroangular region depressed. ABL 5.5-7.7 mm.......Stenolophus (Agonoderus) comma (Fabricius)

Elytral interval #1 darker than background colour of elytron; dark macula of elytron extended anteriorly on interval 2 compared to intervals 3 and 4 (Fig. 309). Scutellar stria proportionately short. Pronotum (Fig. 307) with side slightly sinuate in front of posterior angle which is somewhat obtuse; posteroangular region convex. ABL 5.3-7.2 mm............Stenolophus (Agonoderus) lecontei (Chaudoir)

Current image appears to fit S. lencontei by most criteria above, however, I am bothered that the scutellar striae appear long enough to be S. comma. See specifically BugGuide's Info pages of both species for links to additional comparative photos. Good luck!

… Peter W. Messer, 31 October, 2013 - 9:01pm

Actually we measured it with a ruler alongside,

so we may not have the length you wish. Should we put pressure on the beetle so the head and mandibles are flattened forward? Will that give the true measurement you need? We'll do that later today.

… john and jane balaban, 30 October, 2013 - 3:40pm

By "ruler" I presume you mean a millimeter

scale which is a tool I use frequently laid parallel against ground beetles. I always use my head magnifier loupe (x2) for accurate readings. For example, if I measured ABL between 4.9ish and 5.1ish, then declaring "5.0" does convey useful information way more than just "5 mm". Even a slightly inaccurate declaration, say "5.1" or "5.2", gives more information than "5 mm". Just saying "5 mm" might be anything in roughly the range 4.5 mm - 5.5 mm. On my more compulsive days I remember to include the approximation symbol "~" as in "~5.0 mm" to convey the best available information, that is, the "true" length is in the range "5 mm +/- 0.1mm".

Usually the mandibles don't contribute that much to ABL so I don't bother adjusting head & mandibles unless there is some significant misalignment issue. Too lazy to relax/hydrate the specimen, I do sometimes extrapolate longer by ~0.5 mm if is the head & mandibles are drooping much. When measuring I avoid touching the (dry) specimen in any way to prevent body parts (tiny setae, antennomeres, etc) from breaking. Hope this makes sense.

… Peter W. Messer, 30 October, 2013 - 4:16pm

I you can't get over 5 mm

based on above than maybe your specimen is Acupalpus after all.

… Peter W. Messer, 30 October, 2013 - 6:45pm

Image best fits a palish Stenolophus lecontei

in my opinion. Against much smaller Acupalpus are the following: ABL probably(?) > 5 mm; pronotum shows lateral margin relatively sinuate toward relatively angulated hind corners with apparent coarse punctures; the charactersitic dark color pattern atop elytra. Concern: The shortest of many S. lecontei in my reference collection is ~ 5.5 mm.

Normally the separations among Midwestern Acupalpus-Bradycellus-Stenolophus are quite easy for me with specimen under scope. I blame my frustration on the tricks that photography produces, an unfortunate common theme at BugGuide.net. That's why I offer to do photo-vouchering if accurate species identification would be important to you. It is important to everyone if we were considering a new state record.

J & J, when you and other post ABL (apparent body length) as precise "5.0 mm" (instead of presumed estimate "5 mm") is it fair to assume that you actually measured this from mandibular tip to elytral tip, then rounded to nearest 0.1 mm? I would be more reassured in my current identification if I learned that a remeasurement did indeed show an excess of "5.0 mm". Unfortuately I now planted with you an unavoidable "bias" in any repeat measurement.

… Peter W. Messer, 30 October, 2013 - 8:49am

Moved tentatively

Moved from Beetles.

… v belov, 29 October, 2013 - 8:28pm