I've heard of some people treating their substrate with extreme heat or cold with varying degrees of success. Sometimes they bake their substrate, freeze it in a freezer, leave it outside in the winter. The only thing that I personally do is to visually inspect the mulch as I'm setting up a new tub. I'm sure it only takes one time of finding some bugs or spider hatchlings to change my mind though.

Other treat with chemicals such as PAM (Prevent a Mite), but I would advise against it unless you have a known infestation.

Below is a snippet from the other thread that you might find useful if you want to go down the Ace Hardware route.

--- Snippet ---

I think this is the exact Cypress Mulch I use. I wouldn't recommend ordering it directly online and paying shipping. I called up Ace Hardware directly and they ordered into a local brick n' mortar store for me for FREE. No shipping. Plus I think I only paid like $7 a bag...

http://www.acetogo.com/product/mulch...s-2cf-ace.html

Just call up, give them that SKU number and ask for them to order it into the store. The 1st store I called didn't know what they were talking about and said they'd charge me shipping to get it into the store. The 2nd store looked up inventory in the warehouse and said it would be no problem.