Killing Borer in Wooden Coasters

Sorry if this question already has an answer somewhere, I couldn’t find it online or within this community.

As my first foray into woodworking, I’m making relatively simple wooden coasters from red gum. The red gum has had borer in it previously, which actually lends itself quite nicely to adding interesting patterns in the coasters.

However, the obvious problem is that whether I want to keep these coasters, or sell them for a few bucks, I need to make sure any borer which may still be inside is dead.

I’d like a preferably quick way to make sure the borer inside is dead, and was wondering if there was such a method out there? The coasters are about 1cm thick, and approx 7.5cm wide.

I was thinking of just submerging them in water for eight hours, but I know some insects and larvae can survive for days, weeks, even months if they’re hibernating, with little to no air, and couldn’t find information on if borer fall within this category.

If there is no “quick” method, methods which take some time will also then be acceptable as an answer.

In case it’s pertinent, I live in Australia. So far, the coasters have just been cut to size, but have not yet been sanded or oiled (saving those steps for after I deal with any borer).

EDIT: Accepted the answer from Chris as it (and the method in the comments for that answer) worked just fine for me. Essentially, stuck the coasters in our electric oven for a few hours, which kept the temperature around 65-70 degrees celcius over that time (measured by oven thermometer). Seems to have worked, with no discoloration of the wood, and the small cracks in the wood did not get any bigger. Note that the wood was already mostly dry – something else may have happened for green wood, but regardless, didn’t in my case.