Tiny hamuli of whitefly parasitic wasp

Images taken in a controlled environment or with a posed subject. All subject types.

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rjlittlefield
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Tiny hamuli of whitefly parasitic wasp

Post by rjlittlefield »

Crossed-eye stereo pair, 40X on APS-C, slight crop so about 0.35 mm across the frame. The hamuli are those little hooks you can barely see, that hold the wings together in the middle. We will see them much closer, farther along in the post.

Image

The backstory here is that several months ago the basil plants in my kitchen developed an infestation of whiteflies. To go with the whiteflies, there was also a thriving population of small parasitic wasps, body length about 0.8 mm. Some stacked pictures of recently deceased specimens can be seen HERE, in-the-kitchen pictures of live specimens HERE.

Like all wasps, in flight these little critters link their front and rear wings together so they operate as one, using a set of small hooks called hamuli on the hind wing, that catch a fold along the back of the front wing.

The hamuli that we usually see are on large subjects, where the hamuli take the form of a long row of robust hooks; see for example HERE, HERE, and HERE.

Of course we would expect that a smaller wasp would have smaller hamuli, but I did not anticipate just how small or how few might appear. So I was surprised when I saw the mechanism, in one of my specimens that had expired with its wings still linked. Being surprised, I also got curious, and I took it as an interesting technical challenge to get a decent picture of those tiny hooks.

First try was to simply crop from the 40X NA 0.80 image that is posted at top of page:

Image

That was pretty good, but the wasp was shot from the top, looking through the wing membrane to see the hooks which point upward. I wanted better.


So then I flipped the wasp over and shot from the underside:

Image

That was not much better, because the hooks were then largely hidden by the folded section of front wing membrane that they were hooked onto. (Remember that this is with an NA 0.80 objective, which accepts a cone of light spanning 53 degrees off axis all around any focused feature. Blocking half of that cone essentially reduces the objective to only NA 0.40, losing half the resolution to diffraction plus a lot more contrast loss from the interfering membrane.)


Third try was to select a different specimen, attach a hair to the hind wing to use as a handle, then remove the wing from the wasp and mount the handle on an insect pin. That gave me a set of hooks that were not obscured by membrane, plus more freedom to orient the specimen to get a good point of view.

This image shows the 0.5 mm wing, stuck on a hair, in front of the objective. Just out of view on the left is a hemispherical diffuser, providing about 120 degrees arc of diffused light when the several flashes behind it went off.

Image

And here is the final result, best I could get:

Image

In addition to showing a fairly good view of hamuli, this last image also illustrates some of the vagaries of imaging at high NA. Along the edge of the wing, on the right side of the image, there are a couple of bristles that appear sort of split, as if the bristle had cracked longitudinally and spread slightly apart. That's an artifact. What actually happened is that as each part of those bristles went slightly out of focus, the out-of-focus rendition looked split, perhaps due to that insect pin splitting the illumination. The stacking algorithm decided that the out-of-focus split version looked sharper than the in-focus unsplit version, so of course it preserved the wrong appearance. I thought the artifact was interesting, and it would have been troublesome to fix anyway, so I decided to leave it as rendered.

Speaking of "leaving it as rendered", I decided to sharpen using good old-fashioned USM (Photoshop's unsharp mask) rather than any of new Topaz "AI" tools. The reason for that decision is that I was not comfortable with some of the artifacts that Topaz was introducing. I expect that their training set does not include many images with characteristics like these. Anyway I did not want to wonder later whether some feature was real or produced by an AI, so I went with the basic non-pattern-matching approach used by USM.

Methods & equipment: Nikon BD PlanApo 40X NA 0.80 objective with its collar cut off, Canon T1i camera, multiple flashes at low power. Focus step 0.5 micron for the first two stacks, 346 and 79 source images. For the third stack I dropped down to 0.25 micron, 246 source images. The nominal DOF at NA 0.80 is about 0.69 micron, but I used the much smaller value hoping for some improvement. That was only modestly successful. Comparing the results from processing every frame (0.25 micron spacing) with every other frame (0.5 micron), the finer spacing did produce slightly better clarity of some features, but I could only see the difference in flash-to-compare, not in side-by-side view.

--Rik

Adalbert
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Re: Tiny hamuli of whitefly parasitic wasp

Post by Adalbert »

Hello Rik,
Very interesting story, fantastic photos!
Remember that this is with an NA 0.80 objective, which accepts a cone of light spanning 53 degrees off axis all around any focused feature. Blocking half of that cone essentially reduces the objective to only NA 0.40, losing half the resolution to diffraction plus a lot more contrast loss from the interfering membrane.
Could you explain please what: “Blocking half of that cone” does mean?
Best, ADi

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Re: Tiny hamuli of whitefly parasitic wasp

Post by rjlittlefield »

Adalbert wrote:
Mon Jun 27, 2022 2:47 am
Very interesting story, fantastic photos!
Thanks! I tried to leave out all the bad parts -- there were more than the usual number of frustrations.

Remember that this is with an NA 0.80 objective, which accepts a cone of light spanning 53 degrees off axis all around any focused feature. Blocking half of that cone essentially reduces the objective to only NA 0.40, losing half the resolution to diffraction plus a lot more contrast loss from the interfering membrane.
Could you explain please what: “Blocking half of that cone” does mean?
Suppose the blue "J" is the folded membrane and the golden "J" is the hook, being imaged by the objective from the right. Where the hook is fully exposed, light for imaging is gathered across the full NA 0.80 aperture, about 106 degrees from side to side. But where the hook is behind the membrane, even though it is logically visible, a lot of the imaging light is blocked.

Image

The resulting effective aperture as shown here is only about half as wide in the direction that runs perpendicular to the fold. So instead of a symmetric NA 0.80 aperture, the lens is really acting more like an asymmetric aperture that is 0.80 in one direction but a lot narrower in the opposite direction. The value 0.40 was only an off-the-cuff estimate for illustration, half of 0.80. Working the trig more carefully, blocking half the aperture would give sin(asin(0.80)/2) = NA 0.45 . The actual value varies from place to place depending on what the objective has to see past. But in any case, partly occluding the aperture results in less resolution available for imaging the desired object, combined with further reduced contrast due to OOF light being collected by the occluded part of the aperture.

--Rik

Adalbert
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Re: Tiny hamuli of whitefly parasitic wasp

Post by Adalbert »

Hello Rik,
Thank you for the detailed explanation!
Best,
ADi

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Re: Tiny hamuli of whitefly parasitic wasp

Post by allanwalls »

These are really remarkable images, especially given the extraordinarily challenging setup. Since this subject came up in conversation some weeks ago, I have been chasing after my own images of hamuli, from a number of other diminutive species. But given that my interpretation of the word "diminutive" only requires me to use 20X magnification, I was working with small leaf-cutter bees, and slightly smaller potter wasps - gigantic, relatively speaking. While I was eventually able to capture one or two presentable images, it was a struggle, and a time- and patience-consuming project. So my hat is off to the fellow who would even attempt these shots at that scale. But to present this anatomy, with such astonishing levels of detail and clarity - so much so that it is not unreasonable to postulate a mechanism by which this latching system might operate - is a singular achievement. I am relieved to admit that I do not possess a 40X objective, so any decision to postpone another weekend of housework while attempting, in vain, to replicate this work, is moot. Phew.
Allan

MarkSturtevant
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Re: Tiny hamuli of whitefly parasitic wasp

Post by MarkSturtevant »

Very cool. I've never seen this particular wing coupling mechanism shown in such detail before.
Different insects use various structures to couple their front and hind wings. If I recall correctly from my ancient lessons in entomology, moths like the one in your avatar use a long bristle on the hind wing that fits into a fold on the front wing.
Mark Sturtevant
Dept. of Still Waters

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Re: Tiny hamuli of whitefly parasitic wasp

Post by rjlittlefield »

Thanks for the comments, everyone.
MarkSturtevant wrote:
Sat Jul 02, 2022 10:12 pm
Very cool. I've never seen this particular wing coupling mechanism shown in such detail before.
Different insects use various structures to couple their front and hind wings. If I recall correctly from my ancient lessons in entomology, moths like the one in your avatar use a long bristle on the hind wing that fits into a fold on the front wing.
Mark, your memory is pretty good. Many moths have a long bristle on the hind wing that fits into some sort of pocket on the front wing. For one Noctua pronuba, there is a nice picture on the web at https://www.warrenphotographic.co.uk/20696-large-yellow-underwing-moth-showing-frenulum . But not all moths have them at all, and for some moths the structure is different from a single bristle and pocket. Checking another dried specimen of the same species that produced my avatar, I see that each hind wing has two long spines, running essentially parallel from a common base, that appear to engage a patch of specialized scales on the front wing.

"The Insects // Structure and Function" by R.F. Chapman, 4th Edition, page 193, says that:
Many ... Lepidoptera have a well-developed frenulum which engages with a catch or retinaculum on the underside of the forewing usually near the base of the subcostal vein but sometimes elsewhere. This is frenate coupling. Female noctuids, for instance, have from two to 20 frenular bristles and a retinaculum of forwardly directed hairs on the underside of the cubital vein; in the male, the frenular bristles are fused together to form a single stout spine and the retinaculum is a cuticular clasp on the radial vein.
From this description, I'm guessing that the previously linked picture of Noctua pronuba must show a male, while the specimen of Autographa that I just now checked must be female. It seems quite bizarre that the two genders would have such different anatomical structures to do the same function that is not sexual in nature. But the text seems pretty clear!

I have never looked very closely at these structures. I'll put this on my list for next time I have fresh specimens.

--Rik

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