If you see a cockroach, know that there are more. That's why when I lived in Sydney and I found out about Borax I was soo happy. I hate cockroaches, they are vile. The cockroaches get the Borax powder on their legs and take it back to the nest where it kills the rest of them.
I was visiting my DS, DIL and GSs in a suburb of Brisbane. It was about the first night I was there and I am not sure what happened but a cockroach hit the fan (I heard it) and landed on me while I was in bed, it was a horrible experience. I found out DS had drilled a hole in the floor boards to run a cable through and hadn't sealed it.
DS put a seal on the back door, I sprinkled Borax every where and DD sealed up any little gap along the skirting boards and anywhere else in the house where cockroaches could hide. It did make a difference and since then DS, DIL and GSs have moved very close to the city and don't even have screens on the windows. When I visited them recently were no cockroaches.