The Large Japanese Hornet adult is "fuelled" completely from the sugary
substance it gets from the grubs - adult brings grubs protein rich meat
and grub provides adult with high energy fuel in return.
The reason the Japanese were interested in this substance was that it
was not only rich in energy but had substances which allowed muscles to
utilise(convert into power) the energy at a much higher rate than normal
sugars.
I believe the first experiments were carried out on mice.
It doesn't sound like an easy gathering process - each hornet grub has
to be induced to provide the substance by "tickling" it's mouth. I
believe these hornets are quite rapacious honeybee killers and although
the native Japanese bees can handle them (provided the colony is strong
enough) using a thermal smothering tecknique, European honeybee colonies
are destroyed quite easily.

Alan Riach
Edinburgh, Scotland