here is something i found awhile back when i had the same problem, just one roach siting every couple of months, i used boric acid with flour & used the dough balls & cucumber peels, i havent seen one in 6 months
(beware, make sure that you either use old throw away containers to mix boric acid in or sanitize thoroughly before using again.)
Roaches:
1) Mix equal parts boric acid with flour , sprinkle around cracks and crevices or
2) Mix equal parts boric acid with sugar, sprinkle around cracks and crevices or
3) Mix equal parts boric acid with corn meal, sprinkle around cracks and crevices or
4) Diatomaceous earth (pure silica): sprinkle around flours, cracks and crevices or
5) Cucumber peels: set out on counter tops overnight to repel roaches or
6) Mix Borax with a little brown sugar and flour and sprinkle behind appliances, under sink, and in corners. Cockroaches carry the mixture back to their nests or
7) Heloise's Famous Roach Recipe:
1/4 cup shortening
1/8 cup sugar
8 oz. boric acid
1/2 cup flour
Ample water to form a dough
Mix all, form small balls of dough and set out in open plastic sandwich bags (to retain moisture longer, when hardened, replace with new dough)