How to deal with white flies in a greenhouse?

I have a modestly large greenhouse that I have some tropical plants and temperate annuals in.  White flies infested my cucumbers so I had to remove the plants.  I was hoping the white fly predators would catch up and take out the little buggers but that didn't seem to happen.  Now they've started moving onto other plants in the greenhouse.  I know organic insecticidal soap will take care of them but I don't want to kill the good bugs as well (if there are any).

The greenhouse was open to the outdoors until recently and it may get opened up again if it warms up next week.  Once it's closed up for the winter, there won't be any new good or bad bugs except for those which have procreated inside.

What good bugs are there to eat these little pests?  What other permie solutions are there?  They've been in here for several months so the ecosystem has had time to adjust and repel them.

A nighttime light above a tub of water that contains a fish or 2 should do the work for flying bugs. They go to the light, end up in water, small fish eats them.

Thanks Wayne!  Do you know if white flies, in particular, are attracted to lights?

It's a good technique for flying bugs but i have no idea about specific species.

There are nematode species that way white fly larvae. I've seen that work wonders in container plants. Should be available at a local garden center or you can order online

Thanks Stephen!  My local places don't have anything like that in stock.  They have insecticidal soap and neem oil and one guy said those products don't take out the beneficials.  I'm not sure if I believe that...

After digging around on-line I bought a flock of Delphastus catalinae beetles.  Apparently they love white fly eggs and will eat aphids and spider mites if they get bored.  They should arrive next week and we'll see if they like it here.  I sure hope so for the price.

The local greenhouse guy struggles with all sorts of bugs since they come in on his inventory.  He also suggested a botanigard fungal spray that would take out the whiteflies.  That probably takes out all the other bugs in the greenhouse.