Have got several Hibiscus plants doing very well growing inside, but they
are covered in a small white fly. Several times I have sprayed them with
soapy water (using diluted washing up liquid). It seems to cut down the
numbers for a while, but they soon return.

What is the next step up in this battle? I have been reluctant to turn to
real poisons, not least because the plants are in our living room. Is there
something slightly more toxic I could add to the soapy water. Thanks for
any advice.