Bait the jar with apples or potatoes. Banana peels are most attractive to German cockroaches. Change the bait frequently. If no roaches are trapped in 2 to 3 days, move the traps. Dusting the inside of the jar with talcum powder and using the same baits suggested above is also an effective trap as roaches will be unable to crawl out.
Commercial traps are also available.
When they clean themselves, they get the boric acid into their digestive system. It does not repel the insects before they eat it and gives good residual control. However, it takes about a week to start killing. Silica aerogel dust absorbs and erodes the waterproof layer of wax on the roach s body and causes death by dehydration. Do not apply to food or dishes.