> If [Kraus's study is indicative], then varroa would
> not be expected to
> be able to reproduce to any extent once ambient
> humidity exceeds 80% and ambient temp exceeds
> broodnest temperature,
I'm sorry, I did not make it clear that the bees would need some "help" to get to those conditions.
Even in muggy FL, one would need to limit hive airflow to get the correct "Kraus" incubator conditions.
I was surprised that no one in FL has given Kraus's approach a try yet, with maybe a solid bottom board, an entrance reducer, and some cheap temp/humidity probes.
Kraus's conditions will happen only for very brief periods in the USA, even in muggy Florida summers.
One would need to limit hive airflow severely to achieve and maintain 80% relative humidity (RH) for a brood cycle.
This would be easier to do in very muggy places like summer in FL and Washington DC, but to maintain those conditions would still take some premeditated "hive abuse".
The only place where hives might see 90 F temps with 80% RH conditions for very long would be on the coasts of the Red Sea and the Persian Gulf, where surface water temps hit the 90s in summer, and air temps go higher. (Been there, done that - air so thick, you can cut it into chunks with a knife. But the off-season rates are sooo cheap, and near zero touristicas, which is priceless...)
Broodnest temp runs roughly 90 to 94 F, and an RH of 80% with a temp of 90 F would be very rare except for the exceptions above.
A typical "very humid day" at 90 degrees F will have a dewpoint in the middle 70s F, which yields around 60% relative humidity.
If one did have 90 F and 80% RH, the dew point would be 83 F, and the heat index resulting would be 113 F - the sick, the old, the young and many pets would have started dying without serious A/C well before this, large cities would open "cooling centers" for those without A/C to use.
"Humidity" is misunderstood as "percent of water vapor in the air", but it's a ratio between water vapor (evaporating) and water vapor condensing back into liquid. So, at low humidity, puddles readily evaporate into water vapor. At 100% humidity, the air is saturated, so puddles won't evaporate one bit.
But it gets worse - warm air holds more moisture than cold air. A flask of water-saturated "100% humidity" air at 55 F has less moisture inside the bottle than another bottle filled with water-saturated 75 F air. But both bottles would have the same "100% humidity", despite the higher moisture in the warmer bottle.
So, the better way to talk about humidity is the "dewpoint temperature" - the temperature you’d have to cool off to so that dew can form, given the amount of moisture in the air.
I lived in Ft Lauderdale for over a decade, so I know a bit about humidity and heat.
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