# Treatment Thresholds



## swarm_trapper (Jun 19, 2003)

to find out if your treatment worked and if you need to hit them again. Also to see if you should knock the mites back before the next flow or if they are low enough going into that you can wait. I use a alcohol wash it is my favorite way to do it.


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## Luterra (Sep 7, 2011)

Of 506 hive samples submitted to the Oregon State University Honey Bee Lab last fall:
306 hives (60.5%) had no nosema detected
134 hives (26.5%) had less than 1 million spores per bee
66 hives (13%) had more than 1 million spores per bee

Similarly, for varroa (note that samples were taken after fall treatment, for those beekeepers who treated for mites):
169 (33%) had no mites in the sample
222 (44%) had 0-5% mite infection (i.e. 0-5 mites per 100 bees)
65 (13%) had 5-10% mite infection
50 (10%) had 10-29% mite infection

http://honeybeelab.oregonstate.edu/view/2011_results

Point is, how can one decide when to treat or evaluate treatment effectiveness without monitoring the problem? Better data (i.e. mite counts rather than presence/absence) lead to better decisions. 

As a side note, my hive is among the 506 sampled. It had 22% mite infection and is presently down to about 60 bees and the queen. Oxalic acid in December worked but was too late to save a critical mass of healthy bees. So much for first-year beekeepers not needing to worry about mites...

Mark


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## sqkcrk (Dec 10, 2005)

Luterra said:


> Point is, how can one decide when to treat or evaluate treatment effectiveness without monitoring the problem? Better data (i.e. mite counts rather than presence/absence) lead to better decisions. Mark



Had you known your mite level, would you have treated immediately? I am a commercial beekeeper. Most of the beekeepers that I am really aware of treat their outfits, not their individual colonies, on a regular seasonal basis, not when an individual hive is showing a certain level of infestation. Treatment effectiveness is evaluated by overall hive strength and vigor. If treatments were effective, colonies would be strong and productive.

In the Oregon data, what was the results of wintering over of the different levels of nosema? After treatment? Did those w/ "high" nosema levels treat? Did those who treated for nosema have better wintering? Did they have better/stronger colonies?

Intuitively sampling make a certain sense. My question is "Does it really?". Does it provide us w/ real and meaningful data by which we make descisions that are worthwhile?


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## Specialkayme (Sep 4, 2005)

Are you suggesting, instead, to just periodically treat, whenever the calendar tells us to?


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## Michael Palmer (Dec 29, 2006)

sqkcrk said:


> Intuitively sampling make a certain sense. My question is "Does it really?". Does it provide us w/ real and meaningful data by which we make descisions that are worthwhile?


In the case of Nosema, how does one interpret the test results. Formerly, with N. apis, suggested treatment threshold was 1 million spores. N. ceranae doesn't seem to fit that threshold. The lowest infestation you can cound with hemocytometer is about 50,000 spores/bee. Counts are all over the place with many in the tens of million spores per bee.

New York sampled my bees in 08 and 09. Yards were anywhere from not detectable to 2 million in 08. In 09, similar results but the high end went up to seven million. Looking at wintering results, I can see no correlation between spore count and colony death. I didn't use fumigillin.

So what does the spore count mean?


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## wildbranch2007 (Dec 3, 2008)

Specialkayme said:


> Are you suggesting, instead, to just periodically treat, whenever the calendar tells us to?


for nosema how can you decide to treat with the information available to you? below are some comments from one of Randy Olivers articles, not in any particular order.

Practical note: these studies indicate that N. ceranae remains present as an infection in a colony throughout the year, even if it is not detectable by microscopy. But we don’t know whether these inapparent infections affect colony health



N. ceranae is still in the process of extending its range worldwide, and appears to be most successful in warmer climates. It is of interest that in varroa-free Australia, its invasion does not appear to be causing significant colony losses. Interestingly, although it is well-established in Canada, it is not yet common in some northern European countries, but this may be due to restrictions upon bee imports (Fries 2010).

The general trend appears to be that N. ceranae now predominates in warmer countries, whereas N. apis is better adapted to colder areas. It has been often stated that N. ceranae has displaced N. apis, but more careful analysis suggests that that may not actually be the case


The differences between the detectability of the two nosema species (N. apis typically produces much lower spore counts and is generally only seen in spring and fall) may lead “to an increased chance of detecting N. ceranae over N. apis, which could have biased the impression that N. apis has been displaced” (Higes 2010). 


So, has ceranae actually displaced apis, or have we merely been overlooking its cousin?In order to answer that question, Dr. Raquel Martín-Hernández (2011) carefully analyzed over 2000 bee samples from all across Spain. She found ceranae and apis coexisting throughout country, with ceranae clearly predominant (in roughly 40% of hives), apis hanging in there (in up to 15%), and occasional mixed infections (below 7%). She also found that infection by ceranae was favored in hotter areas of the country, whereas apis succeeded better where winters are colder.


I’m seeing similar indications from other countries (e.g., Gisder 2010), which are appearing to confirm that apis is the more cold-adapted species. As far as seasonality, Martín-Hernández found apis only in the spring and fall, whereas ceranae could be found all year, and notably, once ceranae infects a colony, it almost always persists (detectable with PCR, even if not obvious via spore counts).


So what’s the cause of the seasonality of nosema spore counts? With N. apis it is presumed to be due to the requisites of transmission via dysentery by infected bees in the hive during the winter and colony nutritional stress, and limited by its sensitivity to high temperature. Martín-Hernández (2009, 2010) demonstrated that N. apis can only grow in a narrow range of temperature (about 33°C). N. ceranae, on the other hand, grows readily over a range from 25°C to 37°C. However, N. ceranae spores are surprisingly susceptible to chilling (Fries 2010), which may limit their infectivity at lower temperatures.


It would sure be easier if there were a simple sampling protocol that everyone could follow, and if there were clear treatment (or worry) thresholds based upon nosema spore counts, as there are for varroa (Fig. 4), but alas, I’m sorry to say that there aren’t. <--------


But note that in the U.S. survey graph above, that 2M was the average spore count across the U.S. in April and May of this year, yet I’m not hearing of massive colony collapses, despite very poor conditions in many states.


http://scientificbeekeeping.com/sick-bees-part-13-an-update-on-the-nosema-cousins/


my take on what I have read and done, if you once get diagnosed with nosema, you have nosema in some form or another, it doesn't go away. Since I have time in the fall, and as stated above your bees die even sooner if you have both varieties(and I'm in a very cold climate), I treat every hive that I can. No testing. the fumidil is cheaper than getting wiped out, and I have determined that I can't figure out the difference under a micorscope anyway. Now again reading above for the N.Y. beeks that go south for the winter, and Nosema C. being a bigger potential problem in warmer climates, I would probably treat all hives in the spring also, I think?

Now going on a different post by Mike Johnston also from N.Y. who is doing testing, he is seeing the same nosema counts in June and Oct? That would say to me he has Nosema C.? Yet his bees don't go south and I'm reasonably sure he hasn't brought in any bees from down south?? 

Randy Oliver in his article says he hasn't treated his bees(except for testing) since the early 2000's, and he is in alot warmer climate than N.Y. Now saying that If he Isn't treating a portion of his hives every year, how does he know that his hives wouldn't do even better if they were treated?? So many wonderful argument for and against, again I always err on the side of treating until someone can show me that in a cold climate its not needed.:scratch:


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## wildbranch2007 (Dec 3, 2008)

sqkcrk said:


> Since treatment recommendations for varroa are the same no matter the mite count, if you have them, why bother to sample for them, do mite counts?


I do mite counts only after treatemnts to make sure they were effective, and only then do a few hives randomly, and only test hives if I suspect a problem.
I'm the only beek that I know locally that checks every once in a while, other than people pulling droan brood when in hives.


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## David LaFerney (Jan 14, 2009)

I would think that the more hives you have the more important it would be to measure anything - including disease/parasites - to avoid expensive over or under treatment. On the other hand if you came to the conclusion that you should always perform a treatment at a certain time as a regular cultural practice that would allow you to cut back on expensive testing. The first one is probably more usually right though.


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## sqkcrk (Dec 10, 2005)

Specialkayme said:


> Are you suggesting, instead, to just periodically treat, whenever the calendar tells us to?


Don't listen to an inanament object, use your brain. 

When, in a calendar year, is the best time to treat your bees? Before, after, or during the nectar flow season? Or between nectar flows? Most miticides are prohibited from being used right before a nectar flow and during one. So, in the north, that leaves March, April, May. And then right when the last of the honey supers come off.


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## sqkcrk (Dec 10, 2005)

If Randy Oliver still follows his previously established pattern, he sells half of his 400 hives each year. Then splits the other half. Thereby re-establishing his 400 colony hive count. That is a pretty good mite/disease treatmentfree management technique in itself.


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## Kieck (Dec 2, 2005)

Are the treatment thresholds for _Varroa_ really as low as one mite per hive? Seems awfully low to be treating to me. A threshold must exist, whether it's been pinned down yet or not.

And, even a simple presence/absence test can be useful for making decisions to treat or not, I think. If _Nosema_ doesn't exceed the detection threshold, for example, the hive doesn't get treated. If it does exceed it, the hive gets treated.


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## sqkcrk (Dec 10, 2005)

I understand that rational Kieck, but absence of evidence isn't evidence of absence. No detectable nosema may just mean, not enuf to detect. Many of my samples come "No Disease Found" paired w/ a "2 Million Spores per Bee" from two different yds on the same day. Some folks say it's a matter of the time of day and the bee flight as to what you get for nosema in a sample of bees.

As per varroa thresholds, I would think that a low number would be below the threshold, but in a cpl of brood cycles they could turen into a high level, providing more capability of infection to viruses. So treating a low level infestation of varroa early in the year should be effective at keeping the mite levels low thru the season, it would seem to me.

If your treatment kills 75% of 100 mites in April, isn't that better than killing 75% of (?) in October? (?) being the unknown/somewhat unknowable exponential population growth of Varroa in a colony. Which is something else I haven't gotten a good idea of yet.

What will 2 mites per 300 bees in April turn into by October? What will "No Mites seen on drone brood in March" turn into by October? 15 or 20 per 300 bees. And, in a colony of 60,000 bees in Sept./Oct., what does 10 mites per 300 bees extrapolate to in the hive? 2,000 or 20,000? Obviously enuf to negatively effect overwintering ability. Whatever it is.


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## camero7 (Sep 21, 2009)

This is absolutely the best study of Varroa I've read. Well worth the read. It will make you lower your acceptable mite counts.

http://vshbreeders.org/forum/attachment.php?aid=8


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## Kieck (Dec 2, 2005)

> ... but absence of evidence isn't evidence of absence. -sqkcrk


Absolutely right. That's why consistency of sampling method is very critical. This gets into "false positives" and "false negatives." Honestly, I haven't done _Nosema_ testing to this point. I haven't seen a need (no evidence of sympotoms, no losses to anything unexplained). In the case of mites, consistency in sampling method and understanding that you're looking for a changing slope or steady increase on a graph of mite populations can go a long ways to reducing such errors. I do find mites (so I know I'm not missing them in my sampling), if numbers remain consistently low and I see no symptoms of mite damage to any given hive, I believe I am not erring in the methods I'm using. Why treat if it's not needed? 1) Costs, monetary and time. 2) Risks, both to bees and to others. 3) Potential for resistance to that treatment.



> ... I would think that a low number would be below the threshold, but in a cpl of brood cycles they could turen into a high level, ... -sqkcrk


I agree. Certainly, populations could rise rapidly. They also might not. I am a believer in integrated pest management (IPM), and proponent of the same. As such, I try to wait with treatments and use them as "rescue treatments" if/when pest populations rise to a level where such treatments are needed. I understand why people do not use similar strategies, and each person has to decide individually what sort of strategy to follow.



> ... providing more capability of infection to viruses. -sqkcrk


I'm not sure about that one. I'll confess that my understanding of viruliference among _Varroa_ is not all that deep. However, if the viruses are not present at low populations of mites, those viruses will not be present at higher populations, unless something introduces virus(es). Very small populations of viruliferous mites are likely far more dangerous to bees than larger populations of aviruliferous mites. And I suspect that large populations of viruliferous mites are not significantly more damaging to bees than small populations of viruliferous mites. That may explain at least in part why some beekeepers seem to have "survivor" bees even with mites present, and others do not.



> If your treatment kills 75% of 100 mites in April, isn't that better than killing 75% of (?) in October? (?) being the unknown/somewhat unknowable exponential population growth of Varroa in a colony. -sqkcrk


Again, I agree with this idea. The crux of this statement lies in extrapolating from a current population to a future population. One hundred mites (total?) in a colony in April could turn into huge populations. Or not. That's why I prefer to sample and keep track of numbers. If that population does start to increase at an increasing rate, then it's time to do something about it. If your experience shows that you need to do something already with a given number at a given time, absolutely, do it.



> And, in a colony of 60,000 bees in Sept./Oct., what does 10 mites per 300 bees extrapolate to in the hive? 2,000 or 20,000? -sqkcrk


At the end of the season, brood rearing is likely stopped or slowed to a point that virtually all of the mites must be phoretic (please note that I'm assuming stationary colonies, winter conditions that halt brood production, and mite survival on bees in the cluster). The way I figure it, if you count 10 mites per 300 at that end of the season (often in mid to late October here), I would extrapolate based on the percentages: 10/300 = 3.33 percent, * 60,000 bees = 2,000 mites.

Of course, this assumes 60,000 bees in the hive, and that requires some way to estimate that colony size. Also, any colony that attempts to go through the winter with that size cluster here will likely need either copious amounts of honey or die trying to survive.

More importantly, have the percentages remained consistent throughout the season?


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## Adamd (Apr 18, 2009)

For Varroa I know my hives have varroa therefore I treat with thymol in late summer/fall when the honey supers have been removed. As slide-in boards need to go in for thymol treatment, I naturally monitor but don't count. I also treat with Oxalic Acid between Christmas and New Year when the hive should be broodless. I monitor during the treatment but only for interests sake as I am already treating.

I carry out drone brood uncapping / removal as part of IPM and look at the brood for disease and look at bees for signs of deformed wings too. If I am worried, I will wait for the supers to be removed in any case which is when I would automatically treat.


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## wildbranch2007 (Dec 3, 2008)

http://www.americanbeejournal.com/site/files/828/79344/436207/598079/2012_Proceedings_ABJ.pdf

at low infection rates for both nosemas the bees don't live as long, less foragers.



14.

Huangq, Z.Y., J. Adamq, & A. Jiangq - EFFECT OF SINGLE AND MIXED SPECIES INFECTION OF NOSEMA CERANAE AND NOSEMA APIS ON WORKER FORAGING BEHAVIOR AND LONGEVITY - Nosema ceranae is an emerging intra-cellular fungal parasite that was suggested to play a major role in honey bee colony collapse, especially in Spain (Higes et al. 2008 Environ. Microbiol. 10, 2659–2669). Earlier studies also suggested that N. ceranae is more virulent than N. apis and bees in cages died 8 days after inoculation. Our 2001 data showed clearly that in cage studies, both N. apis (30,000 spores/bee) and N. ceranae (30,000 spores/bee) caused a significant reduction in survival compared to the control (no spores) but the two species did not show any difference in virulence. Furthermore we saw that N. apis and N. ceranae, when mixed at various proportions (1:5, 1:2, 1:1, 2:1, 5:1 ceranae:apis, with a total of 30,000 spores), all bees died significantly earlier than the single species infected bees. 



In this study we tried to determine if this is true also under field conditions. We individually inoculated bees with either 50,000 spores of 

N. ceranae, 50,000 spores of N. apis, or a combination of both species (25,000 spores of each species) and a group of control. 

Fifty bees were tagged and 50 bees were paint marked and they were combined with 500 foragers from a 

Nosema free colony and a queen in a nucleus colony. Bees were surveyed for survival every 4-5 days and foraging observations were done daily for 2 hours per day when bees started foraging. In both trials, mixed infected bees foraged and died earlier than others, with the exception of trial 2, where N. apis infected bees died similarly to mixed infected bees with N. ceranae infected bees showing similar survival as the control. Strangely, juvenile hormone (JH) titers were not significantly higher in 14 day old mixed infected bees even though these bees foraged earlier. Nosema apis infected bees showed the highest JH titers followed by N. ceranae infected bees, with mixed infected bees showing almost identical levels as the control which received no spores (Figure). Previous studies in our laboratory has shown that N. apis can increase JH biosynthesis resulting in higher JH titer in bees, which then causes earlier foraging (cited by Chen and Huang, 2010 Apidologie 41:364-374). 

Our results here show that mixed infected bees with equal spores of both 

N. apis and N. ceranae, not only caused earlier death inside cages, but also did so in field colonies. It is not clear whether this increased virulence is due to a "division of labor" (i.e. totally different pathology) of the two Nosema species, or due to an immune-suppression by N. ceranae, which then enabled N. apis to produce more spores resulting in increased mortality. It is also not clear why mixed infected bees failed to show higher juvenile hormone, which has been shown to be associated with foraging behavior in many studies. 



This research was supported by a USDA NIFA AFRI grant "Managed Pollinator Coordinated Agricultural Project" (2009-85118-05718) and a GREEEN grant from the Michigan State University.


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