Pest indicators

In the community garden this rose is one of many  plants I propagated last year that our vine grower chose to plant near his vines to monitor pests.  If anyone has been to New Zealand (I don't know about elsewhere) they will have seen a rose growing at each end of a row of vines.  They can be inspected so much more easily for pests and if some are found then it is odds on that the vines will have the same ones so will need treatment.