I'd heard bee's like lemongrass.
(edit)
I heard the same... so I tried it.
If you're growing the plant for this purpose good luck to you, I went
the essential (?) oil route.
In times of panic - swarm/disruption/ - a mix of a few drops in a litre of water
appears to have a clustering effect, but the action around the sprayed zone
could be something else.
Other than "smells nice", as an attractant the use of oil in a cottonwool packed
straw - adjacent the bait entrance - is yet to prove anything in just on two
weeks. I could update if that changes.
Bill