Hi all, so the pretty sure it wasn't inflicted by me, the last time I checked the hive was on a not too cold day, and I only checked the super not the brood and very briefly at that just to check for wax moth as I was paranoid having lost a weak hive. The hive was probably the strongest I have, plenty of honey stores/bees and in rude health, hence thinking it was pesticides. It's at my in laws property which is big and pretty isolated, no real pedestrian traffic and a long way from the road so unlikely to be anything malicious. My father in law did spray some weeds with pesticides before this happened (round up), I scolded him telling him not too in future but in fairness he used it only on weeds which he said had no flowers and all done a good 25m plus from the hives. Still puzzled why it only affected the one hive anyway.
Good idea regarding testing the existing frames/comb with other insects or even a bee or two. I'll try that and report back. Thanks again for all the replies