I have the same problem with flies breeding in the damp compost in a warm room. It's a problem to get rid of them. Buying a Venus fly trap plant and putting it beside the money tree pot might help. Otherwise an ordinary fly killer spray helps, but be careful using it if you're got food exposed in the kitchen. Another thing you can do is get a thin layer of cloth, drape it tightly around & across the compost and fix it round the pot with an elastic band so the compost isn't exposed. Water the plant from underneath in the saucer and any flies which breed in the compost won't easily be able to escape and will die.