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Photo#383101
Particularly vexing hymenopteran - Metopius galbaneus - male

Particularly vexing hymenopteran - Metopius galbaneus - Male
Marin County, California, USA
April 7, 2010
Size: 15 mm body length
First off, sorry about all the pins everywhere, I am too eager to find out what this is... Every time I try to key it, it comes out wrong. I found this insect on a Coast Live Oak today, and it seems to have a weird mix of sawfly/wasp characteristics. At first I thought it was a stem sawfly, but the wings don't match - many of the images of that family on here appear to show three closed cells in the hind wings, while my insect has two (like a wasp). It appears to sort of have the "wasp waist" when it is viewed from the side like this, but when viewed from above it looks more like a sawfly. It has two-segmented trochanters on the hindlegs (compatible with either wasps or sawflies), and it was unable to sting. The thorax looks very wasplike to me too, but I just haven't been able to find a match.

Images of this individual: tag all
Particularly vexing hymenopteran - Metopius galbaneus - male Particularly vexing hymenopteran - Metopius galbaneus - male

Moved
Moved from Metopius.

Moved
I suspect this to be Metopius galbaneus Townes, which appears to be the Metopius species that is most commonly collected in the Bay Area as well as other parts of California. In his description of the species, Townes said "The basocentral black area of the tergites varies from a rectangular shape with somewhat concave sides (usually in males) to a U-shaped or V-shaped area, in all cases making a pattern unique among the Nearctic species of Metopius, but somewhat like that in M. errantius californicus." The latter subspecies, which is in the subgenus Peltales was described from two specimens, a female from eastern California and a male from southwestern Oregon. The specimen should be reasonably easy to key out in Townes revision.

Moved from Ichneumon Wasps.

 
Re: Moved
Thanks for the very informative reply, Bob; it certainly is a interesting creature.

 
Note
You're welcome. Here's are some interesting tidbits from the discussion of Metopius in the aforementioned 1959 publication by Townes and Townes: "The genus is worldwide in distribution and contains a large number of species. Collectors, however, consider Metopius to be among the rarest of the ichneumon flies and very few persons have ever found a species common." ... "In flight the end of the adbomen is curled downward as in Eumenes." ... "When captured, all the species (so far observed) give a high-pitched, wasp-like buzz. Metopius and Alomya are the only ichneumonids known to buzz like this."

 
Re: Note
Fascinating... Thinking back on when I first captured it, I do recall it buzzing a lot, but I didn't know that was a unique characteristic for this group of ichneumons. I don't know what it looked like when it flew, but when it was perched or walking around it held its abdomen perfectly straight like a sawfly (another trait that had me confused)... It's only curved in this photo because the abdomen curled up tightly when the wasp died and this was as straight as I could get it without risking damage to the specimen.

Interesting that they are considered to be uncommon - I wonder if they actually have low population numbers or if this is just an observer error because they tend to be relatively inconspicuous? Maybe a little of both? I suspect my professors will be thrilled when I relay this information to them - we were all puzzled trying to key this insect out in the books; nothing seemed like an exact fit.

 
Conspicuousness
My impression is that numbers of Metopius species are rarely numerous and are not commonly collected either by net or by Malaise traps. Rather than inconspicuous, I would regard the species as quite eye-catching, which would seem to explain why there are as many photos of them on BG as there are. I would suppose the relative abundance of the species to relate to in some way to the relative abundance of the hosts, but the hosts of most of the species aren't known. All Metopiinae oviposit in lepidopterous larvae and emerge from the pupa.

Moved

Ichneumon.
Looks clearly like an ichneumon to me...With this great pic Bob Carlson can probably give you a genus name.

 
Thanks for the quick reply!
My insect doesn't have the "horse head" vein pattern in the wings - do some ichneumons not have that feature?

 
Sorta:-)
Well, that "horse head" cell appears divided at the "muzzle." Wing venation does differ even within the Ichneumonidae, too. I'll be curious what Bob says about this one.

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