Unusual articulated tip on wasp antenna (stereo)

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rjlittlefield
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Unusual articulated tip on wasp antenna (stereo)

Post by rjlittlefield »

Let's start with the good stuff. A stereo pair, crossed-eye, 1.24 mm high on subject:

Image

Closer crop, 0.59 mm high on subject:

Image

This is the very tip of a particular kind of wasp antenna, and one that I think is pretty unusual.

This wasp is one of the mud daubers that I presented at http://www.photomacrography.net/forum/v ... hp?t=37174 .

What prompted me to look closely at the antenna were the pictures in that previous thread, particularly the ones in THIS posting.

Here are a couple of examples:

Image

Image

If you look through those pictures, you'll see that some of the antennae are very sharp, some are the usual blunt shape, and there's no clue why there should be some of one and some of the other.

Initially I thought it was just the gender of the wasp, as suggested by the overall body shapes shown above. But that turned out to be wrong.

The real answer turns out to be that sharp or not is at the option of the wasp. The ends of these wasps's antennae have an articulated section, which can be either extended to produce the sharp outline, or retracted to produce the blunt one.

This is the first time that I have ever encountered this structure, but I have to confess that I don't know whether it really is unusual or not. I've looked at a bunch of wasps of a different kind (Polistes dominula) under stereo scope, and I don't see anything like it. But the articulated section is not simple to see when retracted, and maybe I'm just overlooking it. I've also tried Google image searching on "wasp sharp antenna", and I don't see any images that show similar sharp ends. But who knows what that means?

In all the specimens I had, the articulated segment was completely retracted after the subject was dead. To make this image, I had to carefully fish out the retractable segment while the specimen was still fresh, and hold it out by shoving an insect pin into the notch while the specimen dried. Not a simple mount!

If anybody knows about these articulated ends, I would appreciate learning!

For those interested in technique...

Shot with Mitutoyo M Plan Apo 10X NA 0.28 objective with Raynox DCR-150 tube lens, so nominal 10.4X magnification. Canon T1i camera, 15.1 megapixels (4752 x 3168) on 22.3mm x 14.9mm sensor, ISO 100, 1/12 second with diffused Jansjö lighting (3 lamps). 82 frames, 0.005 mm focus step. Shot in portrait orientation, cropped in StereoPhoto Maker to 2758 pixels high for the first image and 1302 pixels high for the second, then resized for posting. Processed in Zerene Stacker with DMap, stereo separation +-1.4%, which for this stack works out to be 5.6 degrees of stereo separation. No retouching.

Here is the setup for shooting. For purposes of aiming I shined a small LED lamp down the eyepiece so as to light up the FOV. The tip of the antenna is bright white in this view because that's the part that was illuminated by the aiming light. Rough positioning of the mounting block was done by rotating in hand under a stereo scope, reproducing that orientation in the high mag setup by pinning the block, then tweaking it with rotary table and goniometer in the positioning stack.

Image

Image

I hope you find some part of this interesting.

Anybody who knows more about the articulating segment, please share!

--Rik

Edit: to fix spelling error in scientific name
Edit: remove question mark from title: "Unusual(?)" --> "Unusual"
Last edited by rjlittlefield on Sun Oct 28, 2018 9:01 pm, edited 2 times in total.

Beatsy
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Post by Beatsy »

Great post Rik. Sorry I can't help with any info, but would just like to comment that this post *perfectly* characterises and encapsulates what draws me to extreme macro! The ability to "see" and explore ever closer, finding new surprises and wrestling with technical puzzles along the way. So much more than just "zooming in". Wonderful stuff!

BugEZ
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Post by BugEZ »

No wisdom to offer on this particular wasp’s anatomy, but a comment...

Bees are often equipped with special tools on their legs to facilitate cleaning, (a scraper to squeegee pollen off the antenna) as well as a pollen basket etc. Mantis that I have photographed have scrubbing pads on the “elbows” of the front legs to help remove the gore of messy meals from their eyes. They can’t blink after all... When called on to give a presentation to cub scouts or brownie scouts, I explain that bug legs are like a Swiss Army knife with tools arrayed along the length. Bugs after all don’t carry a backpack.

In this case the tool is on the antenna and folded in, just like a blade on the Swiss Army knife. Too cool!

Keith

AlxndrBrg
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Post by AlxndrBrg »

Nice pictures, just from seeing the antenna tip I knew it belonged to the Eumeninae, and a male.
Its for some reason a very common modification in the males of several genera of the Eumninae. It's normally not seen on images of live animals, as its on the inside/underside of the antenna. Not sure anyone knows what they are used for really, but I'm sure it's about sex, it always is - unless it's for fighting other males (to be able to have sex...)
Modifications of antennae in males are all over the hymenoptera really

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Post by rjlittlefield »

AlxndrBrg, thank you for the information!

So now I have another question about anatomy of these things.

Here is the tail end of the same specimen (crossed-eye stereo):

Image

Under low power magnification, I had thought that the two spikes looked like maybe two halves of an oddly separated stinger, hence female. Now under much higher effective magnification, I can see that's not the case.

But then I am puzzled. I see nothing like these spikes in photos of the the live animal, so I'm guessing they must be internal and got pushed out in dying and drying.

What are they??

--Rik

AlxndrBrg
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Post by AlxndrBrg »

I was almost contemplating mentioning that males of Eumeninae (and Polistinae, but not Vespinae) have "pseudostingers" on their genitalia. They try to prick (excuse the pun, heh) you when being held, to make you think its about to sting.
Dont know if they serve any additional purpose when it comes to mating, you'd think they would be in the way during the act, but apparently it works out. I think the genitalia splays open during copulation, so they might be held out of the way.
There's other wasp families with pseudostingers too, but then formed from the sternites instead, such as Scoliidae, Tiphiidae, etc. Dont know if I've seen any convincing examples outside Vespoidea, its present in some Pemphredoninae (Crabronidae, Apoidea), but the animals are so small I wonder if they have any predators they could scare with the spines.

The spines and the rest of the genital capsule is kept internally in the abdomen when the animal is alive, but when the abdomen dries and shrinks they protrude. For some reason the genitalia of Eumeninae are more or less useless when it comes to ID'ing them, so there's no real need to extract them before the animal dries.

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Post by rjlittlefield »

Super! Thanks again!

--Rik

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Post by rjlittlefield »

One more set of images for this beast.

Here is a view of the other antenna of the same specimen. This is the one in its normal position, instead of teased out like I did the first one.

Image

This is 61 frames at 0.006 mm spacing, +-0.8% shift, again corresponding to 6 degrees of total stereo separation. This is pure PMax, no retouching. It turned out that for this stack I had too much flash exposure variation to be fully corrected. DMap produced a trippy background, with big fuzzy swirls of light and dark that seemed to be floating in air. I didn't like it very much, so just went with this one instead.

Offhand I don't know the scale on this one. It's obviously a much closer crop.

--Rik

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