I received the following query from a lady in the UK:
Unfortunately, I didn't open this email until the day after. As soon as I read it, I suspected poisoning, but I replied to the lady anyway, though I felt it might be too late. Unfortunately it was. In truth, I suspect my response may not have helped anyway, but I add it here, in the hope that it may be helpful to other visitors.
Please read the entire page.
Points to note from this particular situation:
If a bee is seen simply grooming itself, leave it alone - this is normal insect behaviour.
Grooming helps insects to clean away dirt, parasites, mites and bacteria. In bees, they will also 'groom' pollen from their hairy bodies into pollen baskets.
The issue here then, is that you are likely to only notice something is wrong, if it is probably already too late. Mites are a different story, and I have a whole page dealing with this issue.
This is a real long shot, but if you come across this situation, nevertheless it will cost you nothing to try and help, and only a few minutes of your time.
However, please do not be hard on yourself if the bee dies. You have done all you can.
In the case of poisoning, I recommend putting the dead body of the bee in the dustbin, to ensure no other creatures eat the bee, and ingest the poison (i.e. secondary poisoning).
If you happen to know of anyone who is spraying poisons in the area - especially if it is your local council - you could have a tactful, friendly word. Outline the problems and ask them not to do it again.
If you suspect it is something to do with your own (accidental) actions, then simply learn from it. That's all you can do in such a circumstance. You could also warn others to prevent them making a similar mistake.
If you see a large number of poisoned bees, check whether your country/region has a scheme for reporting bee poisonings, gather specimens - quite a few - and follow the instructions and advice for sending bees to the appropriate analytical authorities. You may also wish to keep a few in case the first sample goes missing.
For more scenarios, see my link: help with bees.