It's inconsistent when I get wood beetles in my firewood from year to year and stack to stack, and may depend on the type of wood, the location, the weather, who knows. This year I burned a stack of 3 year old seasoned red oak that had zero beetles. Some 2 year old white oak a couple stacks down was loaded with beetles and chewed up.
I have taken to making racks that have a 2x4" over a 4x4" on the bottom, to get me off the ground a bit. And I stack in single rows, 1/3 chord to a stack, with air on both faces of the stack and both ends (and the bottom to a lesser extent). I used to also leave the top open to the air for the first year or so, but with pine trees all around, fallen needles would cover the top of the stack and get wet and cause problems. So now I cover the top of my stacks as soon as they are complete.
I started using roofing felt to cover my stacks, on the recommendation of someone here, and it works fantastic. I slice a standard 36" wide piece into two 18" strips, about 10-11' long. That covers the 16" wide 8' long stack with 1-1.5' hanging down the each end. With lots of building projects, I always have a leftover roll of felt around and it's good to use up the leftovers. And it's cheap enough to buy a new roll whenever needed, probably cheaper than tarps. I season wood for 2-3 years before burning, and the felt paper holds up just fine. It tends to "shrink wrap" to the top of the pile in that time, but doesn't leak that I have seen. In some cases, I can reuse it after 2-3 years, but it really depends on how weathered and sun-faded it looks.