I am very interested in prioninae as well. The things I know were found out by accident.
A few years ago before I was into live beetles. I placed an oak log ~ 12 inch diameter and 14 inches long by the base of a large oak tree in my backyard to grow mushrooms on, I drilled 1/4 inch holes all over it and hammered in the spawn plugs. It was getting hit by the sprinkler with well water. I did not get mushrooms but a large longhorn very similar to the one in your photo but black and no tapered Electra, was walking on the log, I caught it for my collection and noticed there was another one. I chopped into it and saw many pupae, the wood was pretty hard still.
I'm planning on breeding them this year, the larva look awesome. I catch them on blacklight sheets all the time.
To breed them get a log like you would a stag beetle, I think a log that is medium decayed and still hard might be very important though.
I can't remember how long the logs were outside to get in that condition but it was under 12 months. The spawn plugs might have helped, maybe just the hard wood, or the drill holes might have been inviting or helped the decaying accelerate, I know the daily water had to be important, the log was wet with the pupa inside it, I put it in a steralite but forgot about them.
This year I'm setting up many logs under oak trees everywhere to bait the beetles to lay eggs
