Will Borax Acid to control insects and small rats?
Borax laundry booster controls insects but I'm not sure about rodents/mammals. I've had great success with ants -- mix half and half with sugar and place counter or wherever they are (assume no children can get it). Likewise roaches ,they really attack it. For limited termites, mix with sawdust; for carpenter ants mix with cellulose...... whatever insect eats. Best thing is, insects take it back to nest to kill colony. Takes a while but much safer than commercial chemicals.
As Sue stated, Boric Acid will kill insects and is especially good for ants, however it won't kill rats. Here's an article for you on that topic.
To get rid of rats, there are several paths to take. Here's another article that should help you with the rats. Wishing you the best.
Either Boric Acid Or Borax can be used as pesticide both are toxic so beware using around kids & pet, neither works on rats