Tuesday, 15 May 2018

An Ich that Can be Scratched

Alongside the expected moths, my light trap often attracts a whole host of non-lepidopterous insects. These mostly consist of very small flies (which I studiously ignore) but one of the more obvious 'extras' are the Ophion wasps, a family of nocturnal parasitic ichneumonids. They're scary feckers, ain't no denying it and yes, I'm just a tad wary of being stung by one. 

Ophion wasp - generic scary bastard thing trying to escape by smashing out a window pane
However, I've finally come to the conclusion that they are not quite as inherently demonic as I've always suspected and indeed present a challenging new direction with which to test my identification skills. Or lack of. I've been in touch with a guy named Gavin Broad, he's essentially the god of all things ichneumon-related and has written various papers, keys and holds occasional workshops on their identification. He even works with them in a professional capacity. I guess somebody has to.

Anyway, Gavin has provided me with a whole suite of identification keys and this afternoon I used them on a suspected Ophion species. What follows is my attempt to walk you through the keys using images that I took down the barrel of my microscope and then added a few 'arty' arrows n' stuff. 

This is going to look awful, I just know it. 

Working my way through the keys wasn't easy. The terminology is truly bizarre. I constantly had to refer to the glossary and illustrations in order to figure out what part of the wasp I was supposed to be looking at. It took me quite a while to get my head around some of the cross-veins, but I think I managed it in the end. As an example, here's the very beginning of the key that leads to family

1a) Fore wing vein 2m-cu present, vein RS+M absent - (Ichneumonidae) 2
1b) Fore wing vein 2m-cu absent, vein RS+M usually present (absent in one genus considered here) - (Braconidae) 16 

2a) Fore wing with one rs-m cross-vein, and this distal to 2m-cu, thus discosubmarginal cell produced beyond 2m-cu; first metasomal tergite lacking glymma, spiracle far behind middle  (Ophioninae) 3
2b) Fore wing with one or two rs-m cross-veins, if one then this proximal to 2m-cu, thus discosubmarginal cell not extending beyond 2m-cu; first metasomal tergite often with glymma, spiracle at or before middle 6

and so on until it finally keyed out at Ophion...

First part of the Ophion key regards the presence (or absence) of an occipital carina and whether it is complete or broken. A what? Yeah, that's exactly what I said too. Here's a pic

I've added the red dots to highlight the position of the occipital carina
Occipital carina present and entire - check! 

Next we need to see the colour of the stemmaticum. Whatever the heck one of those is! Turns out it's the name for the area between the three ocelli on top of the wasp's head

The keys asks if the stemmaticum is testaceous or black. Looks pretty darn testaceous to me
Next we need to check the shape of the scutellum. I already know what a scutellum is, except it's in a different place than I expected it to be and doesn't look anything like any scutellum I've ever seen before. The key requires that we check to see if it's essentially square-shaped or if it narrows at all

I really struggled with this - I think I've marked it correctly
Figuring out quite where the scutellum started and finished was difficult, and I'm still not convinced I have it right. But, if I've interpreted it correctly, it seems to be broader at one end and narrower at the other and not very "squared" at all. Hence I plumped for "it narrows".

Next part of the key was a whole lot easier. Any black on the frons (fancy name for the face)? A simple yes or no, how lovely!

That'll be a resounding "no"
There's an Ophion that could key out here called Ophion minutus. As the name would suggest, it's very small. The wing length will clarify if we have O.minutus or whether we need to carry on keying through. So - wing length max 11mm or substantially larger?

Wing length quite conclusively more than 11mm, so it's not Ophion minutus!
Just to be doubly safe the key says we need to check whether fore wing vein 2r&RS distinctly thickened near junction with pterostigma

Nope, no distinct thickening at the junction with the pterostigma (the coloured cell at edge of wing)
The next couplet in the key really helps us narrow down the options, it also explains why I chose this particular specimen to run through the keys - because I already know what it is*

*though see closing remarks at end of this post.

With conspicuous pale yellow markings on the ocellar area of the head, forming stripes on the mesoscutum, and at the apex of the pterostigma, at least, usually on the mesopleurum too

Pale yellow markings very evident across the mesoscutum (the pale 'braces' on its back)
With pale yellow markings on the mesopleurum too (shoulder area in front of the wing bases)
Our next requirement is to count the antennal flagellomeres. The what then? Basically, we need to count the segments in the antenna. The first segment, the basal one next to the head, is called the scape. The second segment is called the pedicel. After that, all the other segments are the flagellomeres. These wasps tend to have quite long antennae, took a bit of counting to be sure I had the correct total

Clearly there are 66 flagellomeres on one antenna. Rather fewer in the broken one...
The couplet is in three parts, all features need to be used in conjunction with one another to come to a sensible conclusion. So yeah, the first part relates to the number of antennal flagellomeres

6a) Antenna with > 51 flagellomeres
6b) Antenna with < 50 flagellomeres

This has 66, no question about that, so that's definitely ">51 flagellomeres"

6a cont) distance between posterior ocellus and occipital carina much less than 2.0 x maximum width of first flagellomere
6b cont) distance between posterior ocellus and occipital carina c. 2.0 or more x maximum width of first flagellomere

Ok, so what does that mean?  It's not actually as tricky as it at first sounds.

Distance from rear ocellus to carina is definitely less than twice the width of the first antennal flagellomere
We're very almost there, at last! Final part of the couplet leads us directly to a species.

So, still being used in conjunction with the earlier parts of the couplet, hence saying that there are more than 51 antennal flagellomeres (and not less than 50) and that the distance between the posterior ocellus to carina is less than twice the width of the first antennal flagellomere (and not at least twice the width)....

Third metasomal segment, in lateral view, up to 3.0 x as broad apically as at base
third metasomal segment, in lateral view, not more than twice as broad apically as at base

I'd say it is definitely a good 3x broader apically than it is at the basal end
All of which finally leads us to OPHION OBSCURATUS, huzzah!

Of course, the easy way to do it is to say, "oh look, a fair sized Ophion with pale braces. That's obscuratus, nothing else like it". Aah - but is that actually true? Well, it seems not. Ophions across Europe are always single brooded, which is to say that the adults emerge once a year, fly for a short period of time (maybe two or three months) and then disappear until the following year. Ophion obscuratus bucks that trend and has several emergences throughout much of the year. Why should this be? Well, according to research being undertaken by some Swedish scientists, it transpires that 'Ophion obscuratus' appears to be several cryptic species in one. It'll be split out very soon, and presumably we in Britain have at least two or three of the 'new' species present. Oh dear, what a muddle. I'm not sure if they will prove to be 'do-able' on morphological features or if you'd need a DNA kit to tell one from the other. Presumably the time of year each species emerges will be the way to seperate one from the other. It's a case of wait and see. So my carefully keyed obscuratus may, in fact, turn out to be something else entirely...

Music. I used to love this song with a passion, seems a bit lame nowadays but I regularly sang this in my room - much to everyone else's annoyance :) Seemed suitable, seeing as we're all about wasps tonight. Enjoy!



I used to love this one too. Man, I was SO soft metal back then :( 




4 comments:

  1. Much hard work in your Ophion precis, very useful.

    And presumably you are going to write a book about Wasps to confront your phobia?!

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    1. Haha, not exactly phobic. In fact I've just finished keying out a queen Vespula (vulgaris, unfortunately) though it did make me compare it with another Vespula I pinned this time last year...which turned out to be Dolichovespula sylvestris and 'new' for me! I have V.rufa on a pin too. Just goes to show the value of having a reference collection.

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  2. Funnily enough "a fair sized Ophion with pale braces. That's obscuratus". is exactly what I was thinking. Cryptic species, you say. Hmmm. Widowmaker is the best WASP song!

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  3. Gawd! Well done you.

    ReplyDelete