You could try a couple of kilos of dry ice in a slightly excavated mound. Cover it up with a big blue tarp, and it'll diffuse down through the tunnels. Leaves no persistent dangerous residue.
My uncle used to supervise extermination of insects in imported bales of cotton. The huge bales, weighing about 800 lbs were warehoused. The building was hermetically sealed, and they filled it with cyanide. It takes a while to diffuse through a bale that large, but it killed everything. I think that's too risky a trick for a homeowner, or rent-a-pest-killer.

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A third rate theory forbids.
A second rate theory explains after the fact.
A first rate theory predicts.
A. Lomonosov