We use the companion method of planting marigolds/tagetes in the pots/growbags with tomatoes, chillies, etc, against white fly. It seems to work, as we have not been troubled with white fly since we started using this method.
The best method against greenfly is the 'finger and thumb' method.
I would never use the yellow sticky traps in the greenhouse. You may get the odd whitefly, unlikely to get any greenfly, but what you will get are hoverflies, bees, lacewings and other helpful insects. In fact you will catch more helpful insects than bad.
At this time of year, even wasps are helpful, insofar as they will be hunting for insects to feed their larvae. The adult wasps may not eat insects, but that is the sole diet for their larvae, and they are voracious predators to feed them.
valmarg