Powder post beetles are horrible critters!
We have run a sawmill business for 35 years and have provided PPBs with a whole lot of food!
I use a lot of heat to kill 'em, it's got to be over 140 (all the way to the center of the wood) for several hours, and it will kill 'em in all stages of their life cycle.
Never tried any chemical solutions, most of our research on that has indicated it's not as effective as heat, plus I like the heat because it grows on trees!
Our "kiln" is a 9'x20' room with a used woodstove that we run for all it's worth, we can dry 2,500 board feet of fresh cut green lumber down to 6-8% moisture in 2 weeks
If you attempt to dry your wood in any kind of natural/outdoor/ air-dry environment, you might as well plan on feeding them nasty buggers.