Most likely the bugs are already gone. (Bugs only stick around for a few years* - the holes they leave last forever) If you clean the board up and leave it for a while and see no further evidence of new holes or dust you can be reasonably safe in assuming they have gone.
(* See Graphus' comment on possible life spans)
If you think they are still alive, then you have three main options:
If you have a big enough oven, or access to a kiln, heating to wood to a moderate temperature (ie about 56°C) will kill pretty much everything inside, very reliably
If you have access to walk-in freezer, putting the boards in a plastic bag (optional - for humidity) and leaving them in there for several weeks will also kill most bugs.
Probably the most reasonable option available - you can buy pyrethrin spray designed for wood bugs that has a very fine tip applicator that can fit into the holes. Each hole needs to be sprayed. This can be time consuming, but I've found it very effective.