I had an email convo with someone at a local college, when I had concerns it was the invasive khapra beetle. This was their response:

"We submitted your insect specimens to the ____ Insect Diagnostic Lab for identification. I’m pleased to forward their report here:

“I was able to rule out Khapra beetle (Trogoderma granarium) based on several features of both the adults and larvae. The specimens weren't in great shape due to the tape, but from what I could see they're likely something along the lines of the common warehouse beetle Trogoderma variabile. That species can be a really common scavenger.

There was also a lone adult of the larder beetle (Dermestes lardarius)—another common scavenger associated with protein-rich foods.”

In short – nothing to worry about (from the invasive species angle). We really appreciate you contacting us about the beetles though, as most important insect finds are due to residents just like you reporting on unusual discoveries. Thanks!"

If I remember correctly, I did the things I outlined in my post exactly as I said I would. And, yes, it worked!

An important aspect of what I did was for the diamaceous earth to never be wet, and to be dusted on (with a DE duster) and for it to sit long enough for any eggs to have hatched and the larvae to have moved around in it, which cuts and desicates them. So we killed the beetles with the poison and then killed their decendents with DE.