Anatomical details of a blister beetle (Lytta vulnerata)

[rjlittlefield]

This is one of the Blister Beetles, family Meloidae, species Lytta vulnerata based on the date, habit, and black-colored legs. (All the other Lytta's that look similar have reddish brown legs.) There's a good discussion of this species at https://beetlesinthebush.com/2011/10/12 ... a-cooperi/ .

I first encountered this species on a bike ride, in the form of a roadkill corpse. What was left looked maybe interesting enough to take home and put under a stereo scope, so I did that. It turned out that "interesting" was a bit of an understatement, so I went back and collected some fresh specimens, which turned out to be even more interesting.

Here's the first thing that caught my attention: compound claws.



Each foot has two ordinary claws. Then on the outside of each ordinary claw, there's an auxiliary structure that seems to be called a "blade". To my eye, looking at the live specimens that I collected later, the blades appear to be independently actuated. I have no idea what they use the blades for.

For people who can see stereo, here's the everything-in-focus version.



One peculiarity of the everything-in-focus version is that if you look at it not in stereo, it's very easy to misinterpret the structure. At least I get it wrong. Instead of seeing front/front/back/back with only slight separation between claw and blade, I see front/back/front/back with big things in the front and little things in the back, and large separation in both cases. The same thing happens when I look at Figure 1 of https://aces.nmsu.edu/pubs/_circulars/C ... lcome.html .

Next up, we have what look here like donkey ears. What they actually are is tibial spurs, at the joint between tibia and tarsus. In most of the other critters I see, such spurs are pointed like bristles. Why these things have this thickened and flattened structure, I have no idea.






Finally, we have what must be the most frightening male copulatory organ that I personally have ever seen.





If anybody has knowledge of how this anatomy functions, I would be very interested to hear!


All images shot with Mitutoyo M Plan Apo 10X NA 0.28 objective, Raynox DCR-150 tube lens, and Nikon D800E body. Cropping varies: width on subject about 1.4 mm for the non-stereo view of claws, 0.86 mm for the tibial spurs, 1.9 mm for the non-stereo genitalia, and 2.4 mm for the stereo genitalia. Stepped at 0.005 mm.

Stereo pairs are uniformly plus and minus 5 degrees off axis, with percentage shifts computed using the stereo calculator that is now included in Zerene Stacker (in beta build only, at this moment).

--Rik

[WojTek]

Hello Rik,
Really nice claws
Best ADi

[Pau]

What interesting anatomy and good pictures!
the stereos are excellent, the first and third in special

...what must be the most frightening male copulatory organ that I personally have ever seen

ouch!

[rjlittlefield]

...what must be the most frightening male copulatory organ that I personally have ever seen

ouch!

I agree!

I am used to seeing copulatory organs, like butterfly claspers and spider pedipalps, that are often complex but don't strike me as threatening.

On the other hand, a quick search on male beetle genitalia anatomy turns up a number of high-ranking hits that seem relevant, for example an article by National Geographic titled "Horrific beetle sex – why the most successful males have the spikiest penises". But I'm struggling to see how the bold hooks on this Lytta would play some role anything like the bottlebrush spikes shown in the article.

--Rik

[dolphine]

So beautiful and creepy at the same time

[rjlittlefield]

Really nice claws

So beautiful and creepy at the same time

Thanks for the kind words! And dolphine, welcome aboard!

--Rik

[MarkSturtevant]

Very interesting! So each tarsal claw has an accessory 'blade'. From what I have seen, the beetles spend time on flowers, and they eat pollen. So maybe the claws are involved in foraging in pollen.
Insect penises often have various tools used to remove sperm from rival males. I expect their form is one that works well within the female reproductive tract, and those will differ with different species.

[rjlittlefield]

Finally, we have what must be the most frightening male copulatory organ that I personally have ever seen.

(crossed-eye stereo pair)

Today I happened to run across an explanation of this matter.

One puzzling aspect, which I have not previously mentioned, is that the male genitalia as shown are strongly asymmetric -- the two frightening spines are directed to the right side of the abdomen in this ventral view. This subject was dispatched without obvious distortion, so I have wondered if the genitalia are really that strongly asymmetric.

It turns out that the answer is complicated.

In the article by Gupta, A.P. (1966). External Genitalia of Meloidae (Coleoptera). I. The Genitalia and Their Musculature in Lytta vulnerata. Annals of the Entomological Society of America, 59(4), 736-746[*], it is written (pages 741-742) that

The aedeagus (Fig. 10, 12) is well sclerotized, except for a portion of its dorsal wall near its base (AEM, Fig. 10, 12). Distally, it is provided with 3 aedeagal spines, 2 or which are dorsal and 1 ventral. Of the 2 dorsal spines, the distal (DDAS, Fig. 10,12, 13) is slightly smaller than the proximal (PDAS). The ventral spine (VAS, Fig.11-5) is stouter than the dorsal spines, and is fused at its base with the aedeagal wall within the anterior margin of the phallotreme (PHTM, Fig.11) which is situated ventrally.

Then, on page 744,

In L. vulnerata, the natural dorsal and ventral positions of the phallic components are very rarely seen in preserved specimens, and perhaps the same condition exists at rest even in live insects. The genitalia are frequently turned sideways to the left or right, usually at 90°, along the long axis of the body.

Finally on page 745,

The genitalic muscles in both sexes play an important role in the mechanics of copulation. As was stated here, the male genitalic components usually lie on their sides while at rest. Just before copulation, contraction of the protractor of the phallobase rotates the genitalia through 90° by pulling on the genital chamber membrane. The genitalia are thus prepared for copulation. Further contraction of this muscle in its second (posterior) half protracts the phallic structures outside the genital chamber. ... In the female, at about the same time, the dorsal dilators and dorsal oblique dilators, together with the lateral dilator, the lateral oblique dilator, and the 2 rectal muscles, raise the dorsal wall of the inter-segmental sheath, thus opening up the female genitalia for reception of the phalllic organs.
Once the aedeagus is inside the vaginal chamber, it is held in place by the combined action of the retractor of the ventral aedeagal spine and the locking action of the 2 dorsal aedeagal spines in the accessory copulatory apparatus of the female. ...
After copulation, the retractors of the aedeagus draw the aedeagus back into the abdomen of the male.

So now I see, it's all very simple. The males just "dress to one side" when relaxed, and no anatomy is damaged as a result of mating.

--Rik

[*] Accessible behind a paywall at https://www.deepdyve.com/lp/oxford-univ ... 6g3m16vQrD via https://academic.oup.com/aesa/article-a ... /736/92294 .