Celery & celeriac pests / tips

I've given up trying to grow celery from seed - they always seem to keel over when i transplant them... so I've bought some plants from the GC and they seem to be doing well on the plot - they've been in for a couple of weeks and are having a bit of a growth spurt.
I've also planted out some celeriac grown from seed - first time for me with that plant.

I put down slug pellets and beer traps - looking at the wikipedia page for blackfly, celery looks like a favourite of theirs - is that right? I've got a blackfly issue on my broadbeans (as many others seem to have this year) and the celery are very close to them but so far no sign of an infestation on them.

Pip pip,
Balders

I grew celery and celeriac last year and they both grew very well with plenty of watering. The celery didn't suffer any noticeable pests, but the celeriac roots seemed to have been attacked by a small burrowing pest leaving brown tracks through the root. I assume this was carrot root fly as the carrots got destroyed by these as well. I suppose netting is the only answer.