We use Frontline ALWAYS! We have a fairly large flock and go to alot of shows and have to de-louse after each one. frontline is the only product that we have found so far that actually works... dust at $8.00 a can which you have to apply every 3 weeks gets very expensive and is moslty un-effective! Sure frontline is expensive for the small bottle, but when you only use a drop or two on each bird, its last forever and works in just a few days!
When we use it on birds that are in breeding pens, we usually do it under the wing, or if necessary we do it UNDER the vent! (to insure it doesn't ruin fertilization of our eggs)
We never have raised our birds for farm fresh eggs, they are all show stock and raised for hatching eggs/chicks, so I have never had to worry to much about eating the eggs....