Life has been kicking my ass, and been having internet issues at home, so haven't been posting.
So the beetles definitely had more than enough dung for 4-5 dung balls per Orin's Ultimate Guide, and I waited for 7 days past when the dung was all gone from the surface of their tank before digging for brood balls to make sure I didn't interrupt construction. I found no brood balls. I didn't even find anything that appeared to be a half-formed brood ball. I found a couple small clumps of dung, but they didn't look like they'd been handled at all by the beetles beyond being buried.
The way P vindex folds up their legs and plays dead when disturbed makes them really easy to miss when digging through sub, and I thought I lost 2 of them, but they were found during mixing sand into the sub. I currently have about 3:1 organic top soil:sand. The sub feels very different with the sand mixed in, and of course weighs a damn ton.
After mixing the sand in about 2.5 - 3 weeks ago, I haven't seen the beetles once. Not once. I was actually wondering if I stressed them all to death, as there was a solid week in which two fresh piles of dung weren't touched at all, and went to white mold. I should've taken it out, but I left it just in case they didn't care, but unfortunately the mold spreads rapidly once it establishes a foothold, and the next two baseball-sized amounts of dung I gave them were completely covered in mold within a day and a half or less.
It was yesterday morning that I noticed the 1.5-day-old piles were also molded-over, so I was going to remove it all yesterday when I got home from work. I noticed when I got home, though, that there was a fresh pile of sandy substrate mounded up between the 4 dung piles, which is the first evidence I've seen of the beetles being alive in a week or more, so I put it off. This morning, I peeked through the lid and found that the two fresher piles of dung are completely gone from the top of the substrate, and the older two moldy piles are pulled down into the sub and mostly buried in more of the sandy substrate. The mold on them looks to have been crawled all over, as it looks more like a white mat/crust now rather than fuzzy.
Still haven't seen the beetles, unfortunately, but at least a few of them are alive.
They haven't touched the 4 jellies in their container. In fact, 3 of the jellies have grown a tiny bit of mold which I picked off yesterday. I didn't even know jellies would mold, as I've never had them survive this long with adult beetles before.
Now, onto full disclosure: They're getting human dung. I'm ashamed, but only a little. For what it's worth, I don't feel great about it, and my wife simply cannot know.
What I did find when I dug for brood balls was a good handful of fly pupae. I collected them and threw them in a deli cup with no holes in the lid. Apparently, there were more that I missed, because there was an obnoxious boom in housefly activity in my house a couple weeks ago. I'm positive that they hitch-hiked in with the horse dung I was finally able to get, and since horse dung isn't supposed to be great for dung beetles anyway I'm disinclined to try it again. The other types of dung that I experimented with were dog, rat, and human. This was the initial week or so that I had them, and it was the human dung I mentioned them attacking the quickest in my last update. Unfortunately, our rat has died, so that source is gone. The dog dung was the second slowest to be consumed, so I'm not thinking they like it, which makes sense. Since someone with a LOT more experience than myself mentioned human dung probably not being good for rearing, I found someone with a pot-bellied pig and talked them out of some dung, which I offered at the same time as some more human dung. This was the two piles that didn't get touched for a week and got moldy. The pig dung still doesn't appear to have been touched other than being mostly buried just below the surface. The two newest piles of dung that were completely taken/buried as of this morning were both human (as the pig owner wasn't available for me to pick up more).
Since P vindex doesn't live all that long I'm not sure how long to wait now before digging for brood balls. Last time it was 7 days past the disappearance of all of the dung and I found nothing. I'm not sure if the week or so of no activity was due to them being busy "underground" forming and tending brood balls (I hope so). I know that the Ultimate Guide says to check 7 days after the last dung disappears, which is what I did last time, but I'd hate to interrupt brood ball forming at this point with such limited time with them left and as slow as they appear to be with propagating.
One small novel later, I'm done. Back to observing and hoping for eggs.