Ants in historic home

I work in a museum that is situated in a historic home.  We recently
have started to have an issue with ants in our kitchen area.
Housekeeping is not an issue, the kitchen is always kept extremely
clean.  The trail seems to be from behind our dishwasher/sanitizer.
Some actions we have taken include;

    Spreading Borax around the dishwasher

    Placing traps in the kitchen area including behind the
    dishwasher.

    Pulling out the dishwasher and putting a dehumidifier in the
    space to reduce the amount of humidity present.

They seem to go away and then come back.  Unfortunately being in an
historic home, it somewhat comes with the territory, but I would
like to know if there are any other suggestions that can be made in
order to minimize the amount of ants present.

Ashley Stevens
Curator of Collections
Billings Estate National Historic Site
2100 Cabot Street Ottawa, ON Canada K1H 6K1


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                  Conservation DistList Instance 23:28
                 Distributed: Friday, February 5, 2010
                       Message Id: cdl-23-28-022
                                  ***