New Zealand has a problem with the German yellowjacket.  They seem to
have no natural enemies and have increased dramatically since their
accidental introduction a few years ago.
They are a serious problem to humans in the bush and they consume a
lot of tree exudate that our native bird need.
If there is some problem that has hit your population, we would love
to know, particularly if it is exportable.  If you discover it is
some biological control, please let me know.
 
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Arnold Chamove
Massey University Psychology
Palmerston North, New Zealand