Your compost may be to wet, a good breeding ground for pests, in which case take sufficient out to add a layer of shredded paper then cover with the compost you've taken out, this should help dry the compost a little and the layer on top will help the paper decompose.
Whitefly die in cold weather so something else to try would be to leave the lid off your darlek during the night when particularly cold weather is expected...ie... frost but when not expecting rain, this will expose the flies and larva to cold extremes. No rain means your compost isn't exposed to further moisture.
As FG advises a fly trap hung inside the lid is also a good plan or spraying organically with a spray of garlic and olive oil may help. Aphids breath through their skin and this should kill them.
Not sure how helpful this will be...others may be able to provide further advise