> What is an environmentally acceptable chemical to destroy a
> colony in the wall of a house?

I have used as little as 2-3 tsp. of Derris Dust (Rotenone to the US
readers?), a pesticide that is relatively non-toxic to *most* non-target
life forms.  Generally, though, I'd use several tablespoons to be more
certain...

Use a small tube to blow the dust into the entrance of the colony and it is
almost always effective.

Nick Wallingford - Tauranga, New Zealand
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http://www.beekeeping.co.nz