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Thursday, March 25, 2010

Twice Stabbed and Ashy Gray

The other day I noticed a new kind of lady-buggy on the artemisia in the parkway. This was of course very exciting, but I was also sure that it was a twice-stabbed ladybird beetle, genus Chilocorus. Two stab marks, seemed like a reasonable assumption.

So later I was checking bugguide to confirm that and maybe get the species right. Apparently, the coloration on the ventral side of the abdomen is critical to identifying the members of this genus to species. So I put it on my mental list to go out and look at the beetle's underside next day since of course I didn't think to photograph that. Is it really necessary to reveal the beetle was nowhere to be seen the next day? Add to the confusion by finding out several species of ladybirds have the "twice-stabbed" markings of two red dots on black, including variations among the annoying Harmonia axyridis, the dark variation of Olla v-nigrum, Axion plagiatum, as well as the officially twice stabbed (4 or so species) Chilocorus!

Anyway, on closer examination I noticed the Chilocorus and the Axion twice-stabbed lady beetles don't have any white markings on the head or pronotum. But the one in my photos does. Luckily, I found the following deeply clarifying remarks for the species Olla v-nigrum (Ashy gray ladybird) on bugguide:

"Dark form (of ashy gray) can be confused with Chilocorus sp, which have elytra more explanate (appearing more flared) and are a different shape (more "A-frame" basally). Chilocorus sp. never have white markings on head or pronotum. (Ah HA!) (But wait . . . ) Both pale and dark forms (of ashy gray) might be confused with similar forms of Harmonia axyridis, but specific coloration, markings, and shape separate the two. Especially note that O. v-nigrum's spots tend to appear triangular, always with the side sloping away from the suture (where the wings meet) basally. H. axyridis' spots tend to be more of a rounded square."

That clears things up since these spots do not look to me like rounded squares; but then they also don't look like triangles. Another commenter goes on to say that the white edge on O. v-nigrum is thinner and more defined than on the similar H. axyridis. (!) Unfortunately my photos are crappy enough to prevent me from determining the relative thinness of that white area. I am guessing, given the number of times people have been confounded by Asian lady beetles, that this is one of them and not the Ashy gray. At least my ego can take comfort in knowing this particular color variation is relatively rare.

Notice my reflection and that of the chinese elm towering over me on the oh-so slightly explanate and very shiny elytra of the beetle if you enlarge the last photo. I haven't seen another twice-stabbed ashy gray Asian lady beetle, or any other ladybird beetle with similar markings for that matter.

1 comment:

Christine said...

neat! I wonder if the folks at the Lost Ladybug Project would be interested in this. I've seen the drawing of an Ashy in my California Insects, but never in real life (or any of its impostors for that matter!).