Boric acid is regularly used as an insecticide, both as a desiccant and as a stomach poison. Solutions of boric acid used as an insecticide are generally made up as bait. As bait, the boric acid needs to be mixed with a sweetener, so that the taste of boric acid doesn't deter the insect.
Ants and Roaches
Mix boric acid with peanut butter, jelly, or molasses. The concentration of boric acid should be low, around 1%. (Ref. 1.) Higher concentrations deter ants from eating the bait. (Ref. 2.)
Lay the poison in places where you have seen ants or roaches. Do not make it easy for pets or children to get at the bait, despite its being relatively safe to mammals. Do not lay the bait near where food is prepared.
Replenish the baits regularly and allow days or even weeks to pass for enough poison to be consumed to see a difference take effect. Boric acid is a weak poison, and is used more as a desiccant, so don't expect immediate results.
Find the ant nest or anthill, if you're pursing ants, and pour on it boiling water doused with as much boric acid as can be dissolved in the water. (Ref. 2.) In this case, there is no need to confine it to a 1% solution, since its purpose is as a desiccant.
Purchase boric acid pre-dissolved in propylene glycol, for example Bora-Care. Or you can mix it yourself by purchasing propylene glycol in small containers from Home Depot, pool supply stores, or marine supply stores. Propylene glycol is used because it is relatively harmless to mammals but poisonous to insects. Its role though is to dissolve the boric acid so that it can soak into the wood that the termites eat, since termites eat wood from the inside out.
Dissolve the boric acid into the propylene glycol. The more boric acid, the better, but it also needs to seep deeply into the wood. Recommended ratios of solvent to boric acid range from 1-to-1 to 8-to-1, so try a 1-to-4 ratio by volume.
Spread the solution onto the effected wood with a paintbrush or spray pump. If spraying, you may want to prepare the solution in a separate container first. Make sure that no undissolved granules get into the container, as they can clog the spray nozzle.
Apply the solution liberally, because termites eat wood from the inside out. The solution needs to penetrate deeply.
Mix boric acid with sawdust and a sweetener, such as honey or molasses, to be used as a bait. Spread it on the effected wood. (Ref. 3.) Since termites have an affinity for easily chewed wood, another bait option is to soak several pieces of cardboard in a solution, then stack them so that they dry stuck together. The added width makes it easier to position and gives the termites more to eat. A good solution to use is a water-based sugar solution, making the cardboard stick together. Add as much sugar as you can dissolved, then add about 1 to 3% boric acid by volume. (Res. 1.)