Monochamus larva (mature)
Despite considerable research into potential vector species over many years, there is clear evidence that it is only longhorn beetles in the genus Monochamus
that are proven vectors to move nematodes from tree to tree.
This association appears to be co-evolved in that the nematode has a specific biological change in form to the JIV juvenile dauer larva stage that migrates to the beetle pupal chamber and enters the tracheae of the new adult Monochamus
before it emerges from the tree.
Consequently, in all countries where PWN has established, research has concentrated on Monochamus
as the natural transmission medium.