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I had an experience this summer that prompted me to question whether I've been handling varroa in the right way. I hope some of you more experienced folks will share your views.

I've always thought I should assume my colonies are infested, that I should be asking how acute the infestation is, and that I should treat when a treatment threshold is measured. Natural mite drop is commonly described as a useful way to get a rough idea of the infestation level.

This summer I put sticky boards under three of my 28 colonies and got ZERO natural mite drop from any of them in 48 hours. I felt like this result was too good to be true, so I treated one with FormicPro and monitored mite drop. Sure enough, the treated hive dropped more mites than I cared to count in the first day of treatment. I then proceeded to treat all of my colonies.

I'm now questioning everything I know about varroa detection and treatment, and would appreciate your insight:
** Is natural mite drop a reliable method to measure mite loads? If so, I was below the treatment threshold, but wow - there were a lot of mites present! **

  • If every colony is infested, why do we worry so much about treatment thresholds? If we don't treat, won't the fraction of infested bees increase over time - especially in periods when the queen is laying fewer eggs but foundress mites are still going strong?
  • I now think there are two factors that should dictate treatment timing - and neither of them are based on measured mite loads:
* The bees' lifecycle: In my area, the eggs of the bees that will nurse the winter cluster are laid in Aug. and early Sept. Those nurse bees themselves need non-parasitized nurses to maximize their ability to nurse the winter cluster. So, the primary mite treatment needs to happen in late June or early July.
* Nectar flows/climate: The treatments I prefer have min/max temperature requirements. I don't want to treat during or for a couple weeks before a nectar flow if I'm going to harvest honey from the colony. My main spring nectar flow begins while it is still cool in late March/early April, so I don't have much opportunity in spring to treat with anything that has a minimum temperature requirement. I'm done harvesting by late June/early July and then we hit summer dearth and daytime highs frequently in excess of the treatment label maximums. There is not a significant fall flow. Thus, my best opportunities to treat are in early July and in late Sept/early Oct when the bees are not supered and the temps generally are within label requirements.
* Perhaps the early summer treatment should be viewed as the "primary" treatment and timed according to the bees' developmental stages. A secondary treatment in fall would then be administered if mite counts indicate one is needed?

I'll appreciate any insight you can share!
 

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** Is natural mite drop a reliable method to measure mite loads?
Absolutely not.

My experience before we wised up to the fairy tale about sticky boards and mite loads. Our first year with bees, late August, put stickies under two hives, pulled 48 hours later. One of them had one mite, the other hand none. Pondered for a couple days, then decided to put in the treatment (thymol) we had handy anyways, just 'to be sure'. I put in clean stickes, waited 48 hours, then pulled out the stickies. The first one I was counting dead mites, but lost track. Doesn't matter what the final number was anyways, I was past 1000 when I lost track. The other sticky was very obvious, it had significantly more dead mites than the first one.

If you put a sticky under a hive, wait 48 hours, then pull it out and find no mites, it means you have good strong healthy mites that are not falling off the bees.
 

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Sticky boards are about as good as tea leaves... they can spook a new beekeeper in to treating as they finally see and believe they have mites in there hive... but as a way to monitor hives they are poor

If every colony is infested, why do we worry so much about treatment thresholds? If we don't treat, won't the fraction of infested bees increase over time
The thresholds are economic thresholds... something like at X% the mites will impact the productivity of the hives in a month. Treatments cost around $10 a hive, if you have 50 hives and following thresholds saves you one round of treatment thats a good biot of cash...
like wize treating when you hit threshold (more importantly mite counts to tell you you have hit thresholds ) allows you to stave off economic harm..
 

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In the 10+ years I've been keeping bees, I don't think I've heard heard or read anywhere that natural mite drops on sticky boards are a good indicator of an actual mite infestation. I guess the only way they come come somewhat close, is when a colony is brood-less, populous and relatively active. But even then, I wouldn't rely on them for anything more than a piece of the puzzle.
 

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Aylett, VA 10-frame double deep Langstroth
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Learningbee, sounds to me like you are waking up and starting to smell the coffee. Please tell us were you are, your season mimics mine. I calendar treat since waiting for a certain threshold to be reached is simply delaying the inevitable. I use OAV so individual treatments take about 30 seconds and cost around $.05 each, or roughly $.70 (seventy cents) per year per hive.
 
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> Those nurse bees themselves need non-parasitized nurses to maximize their ability to nurse the winter cluster. So, the primary mite treatment needs to happen in late June or early July.

I'm not sure I agree with this statement. Whilst it would be desirable to keep as many bees mite-free and virus-free, treatment in mid-season like this is likely to be a problem with nectar flows.

Midsummer bees live ~6 weeks. If infested with mites during pupation they are either going to emerge with wing deformities (or not emerge at all) and contribute nothing more to the hive, or with high virus loads. However, I don't think there's good evidence that these high virus loads impact nurse bees too badly ... longevity isn't an issue as they're only going to be nurses for a couple of weeks. Maybe they are less effective as nurse bees, but that's not been shown. There's also far fewer mites in early July than late August.

Can the nurse bees transmit the virus? Yes, probably, but whether they can transmit enough to damage winter bees is highly questionable. Oral transmission is very inefficient and/or results in only low viral loads in the recipient. High viral loads result from mite exposure - I'd bet because it bypasses innate immune mechanisms that have evolved to protect bees from environmental pathogens.

I treat to protect my winter bees in late August/early September (Apivar/Amitraz) as soon as the summer honey is taken off. I treat again (oxalic acid) when the colony is broodless. This happens earlier than most beekeepers realise ... this year it was by late October and I treated in early/mid November (still broodless). There's nothing much to be gained by waiting any longer, and you risk the bees starting to rear brood. I'm 56 degrees North on the east coast of Scotland.

Orally bees need to be exposed to millions of infectious DWV particles to get infected. Is it even at that level in brood food? Via mites 10-100 is more than enough, and the virus amplifies a million fold within 24-36 hours.

Don't worry about the bees that rear the winter bees ... and don't worry too much about natural mite drop. The latter varies according to the temperature, the activity of the hive, the laying rate of the queen and no doubt other thing as well.


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David
www.theapiarist.org
 

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David, thank you for posting the above links. I would encourage everyone to click on them and read the articles you wrote.
 

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My fav non invasive way to count is 24 hours after a single dose of OAV. We call this the dead drop count or DDC. Then take that count to mitecalculator to convert it to infestation rate. I use sticky boards through the year as a trend indicator but never as a passive mite level test.

This method is especially useful in fall when the need to inspect the brood nest is less necessary and not desired. Its at that time I work with the top of the stack.
 

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> Those nurse bees themselves need non-parasitized nurses to maximize their ability to nurse the winter cluster. So, the primary mite treatment needs to happen in late June or early July.

I'm not sure I agree with this statement. Whilst it would be desirable to keep as many bees mite-free and virus-free, treatment in mid-season like this is likely to be a problem with nectar flows.

Midsummer bees live ~6 weeks. If infested with mites during pupation they are either going to emerge with wing deformities (or not emerge at all) and contribute nothing more to the hive, or with high virus loads. However, I don't think there's good evidence that these high virus loads impact nurse bees too badly ... longevity isn't an issue as they're only going to be nurses for a couple of weeks. Maybe they are less effective as nurse bees, but that's not been shown. There's also far fewer mites in early July than late August.

Can the nurse bees transmit the virus? Yes, probably, but whether they can transmit enough to damage winter bees is highly questionable. Oral transmission is very inefficient and/or results in only low viral loads in the recipient. High viral loads result from mite exposure - I'd bet because it bypasses innate immune mechanisms that have evolved to protect bees from environmental pathogens.

I treat to protect my winter bees in late August/early September (Apivar/Amitraz) as soon as the summer honey is taken off. I treat again (oxalic acid) when the colony is broodless. This happens earlier than most beekeepers realise ... this year it was by late October and I treated in early/mid November (still broodless). There's nothing much to be gained by waiting any longer, and you risk the bees starting to rear brood. I'm 56 degrees North on the east coast of Scotland.

Orally bees need to be exposed to millions of infectious DWV particles to get infected. Is it even at that level in brood food? Via mites 10-100 is more than enough, and the virus amplifies a million fold within 24-36 hours.

Don't worry about the bees that rear the winter bees ... and don't worry too much about natural mite drop. The latter varies according to the temperature, the activity of the hive, the laying rate of the queen and no doubt other thing as well.


--
David
www.theapiarist.org
This is defiantly an area specific statement you made. In the South if we don't treat in June and July right after pulling honey lots of hives won't make it until Sept. They build up on the spring flow raising bees and mites. Then as soon as you pull honey and the queens slow down the mites will start taking out hives. I like to treat in June/ July and again in late Sept. Oct.
 
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