You asked in a comment how to kill the bugs - really you should make a separate question but regardless:
Take the tree stumps and put them in heavy duty plastic bags (one per bag) and set them outside in a covered area. Leave enough room in each bag for a plastic container of some kind to fit (a tupperware bowl or quart sized container like you might get wonton soup delivered in, whatever...)
Get some dry ice pellets - an internet search will help you find a local provider. They're more common than you might think. You only need about 2 pounds of pellets but more won't hurt.
Fill each plastic container with pellets and put them in the bag.
Now LOOSELY close the bag ensuring that the opening of the bag is up high - but don't make an air-tight seal.
The CO2 pellets will gradually dissolve into pure carbon dioxide gas. CO2 gas is heavier than air, so the idea here is to trap the gas inside the bags - but allow enough venting so pressure doesn't build up and rupture the bag. As the CO2 fills the bag it will push lighter gasses (like oxygen) out.
Insects are dependent upon Oxygen just like us and so with a bag full of CO2, they will die from CO2 poisoning.
Leave the bags sit until almost all of the pellets have dissipated. Seal the bag more tightly and let it sit for 24 hours just to ensure good killing of the bugs.
Remove the logs and the insects should be dead.
(This also works to kill rodent infestations - put the pellets in the ground and bury them. CO2 will expand, sink to fill the nests, and push out the good air)