mites in first brood

[peterdbk]

The 3feb12 diary post said "some claim that all the phoretic mites enter the first brood after a broodless period, but Randy said he did not observe this."

I have read these claims also and want to see some hard proof before I put much at risk with attempting to treat on that basis. I think we know that the percentage of mites in the brood varies with the season. Take the case of colonies rearing small amounts of brood late in the fall. I've had colonies with moderate mite levels at that time and they have been able to raise brood. From this I've suspected that most mites are not in the brood at that time.

The other way to look at it is to consider a colony with 20000 bees, 2000 mites and 500 brood cells in mid winter. If all those mites piled into that brood, all the brood would die, the mites would not produce successful offspring, and many or most of the mites would die. I think the mites have evolved to be smarter than that.

When a colony first starts to raise brood in winter, it only needs a small number of nurse bees. It is the mites on those nurse bees that have access to brood cells. Many other bees have the potential to be nurse bees later, and have mites on them, but these mites are not 'in play' because their hosts bees are not caring for brood. That is my present mental model.

[Allen Dick]

Your position makes sense to me.

Mel makes that claim as to this cell-loading phenomenon being part of the reason that a broodless period results in mite control. Personally, I doubted it and asked on BEE-L. No one could corroborate the claim.

I'm more inclined to think that, seeing as the longest life expectancy for a phoretic mite is about 90 days and the mean somewhere around half that, and seeing as at any given time, very roughly half the mites would be halfway through that 45 days, in 22 days of queenlessness, a large percentage -- very roughly 3/4? --would bite the dust naturally with no additional help. Many more might be too old to reproduce once the brood starts up again.

[peterdbk]

> the longest life expectancy for a phoretic mite is about 90 days and the mean somewhere
> around half that
How solid is your info about mite life expectancy? Does that assume mortality is just old age or is some component the result of grooming or other aggression by bees? Did the study consider the possibility that mites may behave differently in a winter cluster so as to lengthen their lifespan?

It is my mental model that Russian bees raise little or no brood for a long stretch of the winter. I have not seen that property get credit for Russians getting mite counts down. Instead, I have seen Russians credited with enhanced grooming and "other" traits to account for mite suppression.

I also wonder how much brood rearing actually takes place in the winter in the north with bees adapted for the north. I've never wanted to disturb my bees enough to make careful observations. However, the occasional observation over the years with New World Carniolans suggested to me that there were a few (1-2) bursts of brood rearing in the winter apparently triggered by warm spells. There is also the question of where the pollen would come from for bees to raise significant brood for 2+ months in Alberta before natural pollen comes in. In your old practice of bulk syrup feeding in the fall, your hives would fill a deep with syrup within a few days. There was not time for them to collect and store a large amount of pollen under that syrup.

Something tells me that the information I have about mite survival, winter brood rearing, and food supply, can not all be true at the same time.

[cam bishop]

Peter,

I agree that some mites must live longer than reported. Otherwise there would not be the spring problems we see in the colder climates. I'm not that far from you and I haven't seen much brood rearing, even in a couple of Italian hives I have until late February or early March.

[Allen Dick]

> How solid is your info about mite life expectancy?

I don't know. The study was somewhat artificial, but the best I could find. I showed charts from it sometime back over he last 105 days. I may dig it up again, but not right now. I found it reasonably convincing.

> Did the study consider the possibility that mites may behave differently in a winter cluster so as to lengthen their lifespan?

No, and that is something I wonder about. I would really like to see some studies of varroa populations over winter in cold climates.

> I also wonder how much brood rearing actually takes place in the winter in the north with bees adapted for the north.

Quite a lot, actually. Most hives have about 20 to 100 square inches of brood after the fall broodless period.

> There is also the question of where the pollen would come from for bees to raise significant brood for 2+ months in Alberta before natural pollen comes in.

They get the protein from bee bread and their own bodies AFAIK.

> In your old practice of bulk syrup feeding in the fall, your hives would fill a deep with syrup within a few days. There was not time for them to collect and store a large amount of pollen under that syrup.

Actually, I fed in stages and if they filled brood combs, there was some pollen there. Maybe not a lot, but enough to raise some brood.

> Something tells me that the information I have about mite survival, winter brood rearing, and food supply, can not all be true at the same time.

There are unknowns, that is for sure.

> I agree that some mites must live longer than reported. Otherwise there would not be the spring problems we see in the colder climates. I'm not that far from you and I haven't seen much brood rearing, even in a couple of Italian hives I have until late February or early March.

How much does it take? How many have to survive?