Whitefly? in the GH. Help!

Do you keep it closed up during the day?

I think at this time of year if you don't act fast they will multiply before your eyes.

You can use insects to eat them? Not sure what they are called?

Sticky tapes.

I would empty the greenhouse, wash all your plants. Keep the really infested ones outside.

Wash greenhouse thoroughly.

Fleece plants for a couple of nights outside?? What plants have you got in there?