HI Vince-
Kevin Christensen is right-  you don't need to prime if you keep the larvae
wet.  In central California right now, we don't need to do anything to keep
the grafts warm.  It's already reached 99 degrees F around here a week or so
ago.
 
We graft in a drafty, hundred-year old hay barn.  I do nothing to coddle the
grafted larvae except to place each completed bar under a water-saturated
folded towel until I complete a frame.  Then I pick up the frame and walk out
to put it into a builder.  I routinely get close to 100 percent acceptance
under these primitive conditions, as long as the larvae are wet.  In fact, I
don't think you have to keep grafted larvae warm at all.
 
Lately, we use the the Chinese buffalo-horn grafting tool.  If you make up a
breeder system that provides you with well-fed (floating) larvae, then the
Chinese tool is ideal.  It will pick up the larva and the *entire* puddle of
royal jelly at once.  You don't even need to be careful about the orientation
of the larvae to the tool-just scoop them up, and plop them into the cell
cup.  They will not dry out, because you have the entire pool of royal jelly.
 Try these tools out- they make grafting much quicker.
 
Regarding temperature sensitivity of larvae, I think it's highly over-rated.
 I've taken frames of day-old larvae that I had grafted from--and  poorly
washed out with cool water-- and leaned them against the side of a hive to be
cleaned.  After a cool, completely exposed night (California, okay-- 45
degrees F), the washed, day-old larvae were completely viable and grew into
sealed brood after I gave the frame back to the breeder the next afternoon.
 
Kevin didn't say this, but I eat a lot of of larvae licking the grafting tool
clean and I'll bet he does, too.
 
Kevin Roberts
Hollister, California