At what portion of the game will Brute Splicers stop appearing?

The "Research Camera" article at the BioShock wiki states:

Brute Splicers stop appearing for a portion of the game, although they re-appear near the end, so it is important to research them sooner rather than later.

I would like to make sure to fully research Brute Splicers before they stop appearing (as they'll only appear again near the end of the game).

At what portion of the game will Brute Splicers stop appearing? (Before they re-appear near the end of the game.)

Note: Can't find any info about this at the "Brute Splicer" article at the BioShock wiki.

I failed to finish researching Brute Splicers by a few points, before they stopped appearing.

From my experience, they stop appearing at Dionysus Park (the sixth level). So make sure to fully research them before leaving Siren Alley (the fifth level), if you want to get the research rewards, including the Armored Shell 2 gene tonic at an earlier part of the game.

They will re-appear again near the end of the game (at the final levels, Outer Persephone and Inner Persephone).

Source: Personal experience, and from verifying it at the walkthrough guides at GameFAQs. The walkthrough guides don't mention Brute Splicers appearing at Dionysus Park, and mentioning them appearing again near the end, at Persephone.

As far as I can remember from my game, the Brutes stop spawning when you reach

Fontaine Futuristics

and start respawning (huge loads of them) at the very last level of the game, so you better complete the research before you reach that level!

I'm sorry I could not provide a valid linkable source for this, but there seems to be none around except forums where people posts their gameplay experience