Thanks!!
First, yous new photos confirm the Rh. iracundus nymph I saw you:
http://www.biodiversidadvirtual.org/insectarium/Rhynocoris+iracundus-img7502.html
Second, these drawings confirm your assessment (I want say "opinion"but Google Traslate traslate very rare :) ). For now, I should really consider you're right.
Thanks again.

I added nymphs-pictures for Rh.annulatus, iracundus, niger, punctiventris:
http://barry.fotopage.ru/gallery/determination.php?id=918

I looked up the description. This is Rh. annulatus. I'll show You a picture ...

Well, If you say that it is Rh. punctiventris, you must be right. Discarded.
Rh. iracundus, all things considered, it may be but in principle I doubt despite the variability of the nymphs.
I observed your photos that you have Rh. iracundus very red phenotypes color and widespread. Nymphs may appear rather to this:
http://www.biodiversidadvirtual.org/insectarium/Rhynocoris+iracundus-img7502.html
Note that it has multiple color bands on the legs, not only one. It's the same case as Rh. annulatus, their nymphs also has 2 rings on femora I and III and only one or none in the II.

In this case, we need more encounters :)

Definitely Rhynocoris sp. nymph.
Ciao!!

PS. Thank you! I have to look at the pictures - some use ...

Rhynocoris punctiventris for Kharkov is very unlikely. He is described only in the south of the Crimea (the mountains). Maybe it's a Rhynocoris iracundus? It is more likely. We also have Rhynocoris annulatus. R. niger to Kharkov is not given, but is more likely to Kharkov than punctiventris.

It's Rhynocoris sp. nymph.
I'm not sure for the species, but looking at your "Определитель" but looking at your "Определитель" and noting that Fauna Europea mentioned only four species in Ukraine:
Rhynocoris (Rhynocoris) annulatus (Linnaeus 1758)
Rhynocoris (Rhynocoris) iracundus (Poda 1761)
Rhynocoris (Rhynocoris) niger (Herrich-Schaeffer 1842)
Rhynocoris (Rhynocoris) punctiventris (Herrich-Schaeffer 1846)

... I think the chances are Rhynocoris nigriventris.
Both Rhynocoris annulatus as Rhynocoris iracundus are eliminated by the number of rings they have in their femurs, and Rhynocoris niger isn't possible because it's very browm and black.

Well, I've seen that your "Определитель" have not put images or Rhynocoris erythropus and Rhynocoris cuspidatus.
I invite you to see them (although I'm sure you know the photos from the Internet) on our website:
http://www.biodiversidadvirtual.org/insectarium/Rhynocoris+R+erythropus+Linnaeus+1767+87-cat8686.html
http://www.biodiversidadvirtual.org/insectarium/Rhynocoris+R+cuspidatus+Ribaut+1921+132-cat14159.html
Ciao!!