What gage needle and length did you use?
I don't have a clue about the proper design for a suction assisted grafting tool. In my hack of an attempt to make my syringe/needle a suction unit I found out immediately there was no way I cold get it to work without a fair amount of tinkering. I was/am not in a position currently to tinker with this idea although I do feel there is a possibility it could work.Interesting idea!
In a former career... we used vacuum pencils for delicate pick & place operations such as shown in these links.
http://www.vaccon.com/Cups-Pencil.aspx
&
http://www.vaccon.com/Cups-Probes.aspx
On the site it shows the smallest tip is .050" which is probably still too big, but I wonder if you fished your wire in the end, and then epoxied the tip shut, and then pulled the wire if that would leave a hole small enough to hold the larva safely.
Thanks for sharing.
Dave.