# Calculating Mite Load Using Post-Treatment Drop



## Bee Arthur (Mar 21, 2015)

I've been using oxalic acid vaporization for a couple years and it works great to kill mites with no apparent harm to my bees. The only part of the process I dislike is doing the sugar rolls to calculate the pre- and post-test mite load. This testing process is intrusive and I'm always afraid I'll harm the queen doing it.

So I've created a "calculator" that uses known mite levels and the resulting mite drops to attempt to estimate mite loads without having to do frequent tests before and after treatments. The idea is I continue to test and treat as I have, building up my sample data, and eventually do invasive testing only for special circumstances. Otherwise, I'll stick with my learned treatment regimen, with mite loads and follow-up treatment decisions derived from the post-treatment mite falls.

I just put this together in the last couple days, so if you see any glaring oversights I'm happy to hear them. If the predicted numbers prove close to reality over the next year, I'll share the spreadsheet with anyone interested.

Here's a screen shot of the xls. I'm entering sample data on the top; the blue cells near the bottom will be the only required entries once the data is proven accurate. If, over time, there doesn't appear to be a good correlation between mite drop and mite load, I'll abandon this effort. I realize there are variables that may affect these numbers--namely, I've seen some people say the highest mite kill is 2-3 days after treatment. For this reason, I'll try to get my mite drop samples within 24 hours of the treatment to avoid this potential upward curve in the kill rate.


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## Mike Gillmore (Feb 25, 2006)

Looks interesting.

Is there a reason you don't do your counts after 48 hours? I would think that would give you a more accurate kill rate to work with.


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## Harley Craig (Sep 18, 2012)

your biggest variable is going to be mites under capped brood. You need to work in the number of capped brood frames into your correction.


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## wdale (Jun 27, 2014)

Try out calculator the Brits have made a lot easier to work with Works excellent with sticky board counts and drone cell counts I use for 1-2 days and multiply out for seven days
I have used this for a few years and found that 3-4 mites a day depends on the month is my IPM 

https://secure.fera.defra.gov.uk/beebase/public/BeeDiseases/varroaCalculator.cfm


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## larryh (Jul 28, 2014)

Harley Craig said:


> your biggest variable is going to be mites under capped brood. You need to work in the number of capped brood frames into your correction.


I'm a little slow. Why does that matter? Is the amount of capped brood considered when you do an alcohol wash or sugar shake?


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## Harley Craig (Sep 18, 2012)

larryh said:


> I'm a little slow. Why does that matter? Is the amount of capped brood considered when you do an alcohol wash or sugar shake?


I guss im the one thats a little slow and dont understand what you are trying to acomplish


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## Bee Arthur (Mar 21, 2015)

Thanks for the comments everyone. I'll consider them all more deeply during my next day off of work.

But quickly, here are a couple notes...

I had thought the same thing as larryh regarding the capped mites. The alcohol wash and the powdered sugar roll don't account for the capped brood, so I didn't think it was necessary in this case either. However, if I can find some decent data on what percentage of the mites are in with the brood, I think I'll make that a factor somehow.

I've usually done 1-day mite drop counts because I prefer to keep the screened bottom board open. I know it's probably an irrational instinct, but I've never kept bees in solid bottom hives so I guess that's why I always feel compelled to get the hives opened back up.

Regarding the British calculator, I had seen that before and it didn't really do what I'd hoped it would do. It relies on a natural mite drop and not a post-treatment mite drop, which (in my mind) has a lot to do with bees' hygienic behavior. Hitting them with OAV forces mites to the sticky board independent of the bees' behavior. That calculator also requires really generic inputs with very limited variables. For instance, it makes no (overt) attempt to describe the population of the hive, which I think would have a huge impact on the mite fall (especially a natural mite fall). 

Anyway, those are quick thoughts. I'll fiddle with this more over coming months and maybe I can come up with something useful. Or maybe I'll just have fun failing to come up with something useful.


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## Daniel Y (Sep 12, 2011)

In my way of thinking, all that a mite drop really tells you is exactly how many mites are no longer a threat to your bees. Yes a very literal perspective but that is where I tend to start my assessments. To then estimate what that may mean in regards to mites that remain a threat requires more than just a mite drop count. This estimate falls directly in what I call Assertion. Assertion is an assumption based upon at least some evidence. Now we all know about assumptions and assertions are only slightly better. So at the very best you can expect to get a poor result. Even if you do a thorough job of collecting the evidences you are at best making a guess. The best evidence in my opinion is that evidence based upon past experiences. Since most of the actual results are local and even colony related. Is there a lot of capped brood or little? what time of year? what mode or period are your bees in. Honey production, brood production in a pause between brood production and honey production. winter prep build up etc. A low mite drop during periods of high capped cell counts could be devastating news. while a higher drop count during broodless or near broodless periods may mean all is fine. What I would like to see set down is a brood cell factor. Such as a multiplier based upon every frame of capped cells into eh hive. So you get a mite drop of 5 mites in a 24 hour period you then multiply that number by some factor based upon number of frames of capped brood. say double it for every frame of capped brood so if you have 10 frames of capped brood it would represent a comparable drop of 55 mites if there where no capped brood at all. Now those numbers are purely made up and have no actual mite count history behind them. This would allow beekeepers to arrive at an adjusted mite drop based upon a set value. the importance of this is that reported mite drops from various beekeepers would become more consistent rather than estimates based upon various random guessing and estimating. Maybe even end up with a daily mite count index. sort of like looking up the air quality in your area. look up the maximum acceptable mite drop for you area for that day.


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