Bob

> I think that location has a lot to do with what works best.

I am sure that you are right there.  But...

> Thymol and formic cannot be used if the daytime temperature is above 30C 
> because of brood and queen issues.

I used thymol crystals in India with a temperature of 37ºC.  Cut the dose 
from 8g to 4g.  No problems.

>Britain doesn't often get the extremes we see here.

OK , so it only hit 28ºC when I was treating at the beginning of August - 
but that was the temperature in the shade and hives in full sun would have 
had it a lot hotter.  Personally, I do not buy this temperature argument. 
We all know that colonies regulate the temperature in the hive and can 
prevent meltdown when it is 40ºC+ and can certainly rear brood when it is 
way below freezing (we had -14ºC for days on end earlier this year).

What matters for successful use of thymol is the amount of brood present. 
No brood = low hive temperature = thymol does not evaporate (or deliquesce). 
We find that if there is brood its works, if not results are poor.  This the 
reason that we can treat colonies returning from the heather in September 
successfully - the heather gives a boost to brood rearing and the then 
thymol works; if we treated our non-heather colonies so late the thymol 
would just sit there.

Best wishes

Peter
52.194546, -1.673618 

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