BIG MYSTERY by beekeeper Fred

This story is provided to everyone in hopes we will all learn something from this experience.

Just when you think you are beginning to get a handle on successfully handling bees they spring another surprise on you.  My beekeeping friend Jon had a good summer.  He raised more than one hundred queens and also got a decent honey harvest.  It wasn’t as much as he wanted, but with this summer’s weird weather many of us had a smaller honey harvest than expected.  At the time of his honey harvest in early September all hives seemed up to snuff.  I remember remarking in late September that some had booming populations.  In mid-September Jon started fall feeding.   A few hives seemed to not be taking in the syrup, but most were rapidly draining the feeders.   Nothing abnormal.

In mid-October Jon set about removing the feeders in order to get the hives set for winter.  He immediately noticed sometime was amiss.  The bees in the first four hives appeared to have absconded.   Things didn’t get any better as he went through his apiary.  Probably about 25% of the hives still had bees, but then it was usually only a small cluster of insufficient size to survive the coming winter.  In the course of a month his apiary was essentially wiped out; a 75% loss and winter had not even started.   During the same time frame, I had only one hive “abscond” in a similar manner while I was feeding it.  Jon thought by putting our heads together we might be able to deduce what happened.   

We went through several hives.  There were varroa on the bottom boards, but nothing out of the ordinary considering the bottom board was last cleaned in the spring.   There were very little or no dead bees in the hives.  Most hives at this point were being robbed by yellow jacket hornets.  We didn’t determine if the hornets were after brood or honey.   Three hives that we looked at still had small clusters and their queens.  It was like his apiary had been hit by CCD (colony collapse disorder) as seen on some videos; all bees gone but the queen and a few bees.   Use of the CCD handle has declined in recent years as understanding of varroa and bee viruses has improved. 

We then tried to figure out what had happened.   We wanted to chase down all leads to the best of our ability.   A call to the State Bee Inspector was to put it mildly a little dissatisfying.  It seems the standard answer nowadays is ”Varroa, Varroa, Varroa”.  This answer could be the cause, but we hesitant to blame these heavy losses on something so simple and so quickly.   The inspector saw no reason for a visit or getting a sample of bees from the still surviving small clusters.   We decided to try to analyze the situation ourselves, but without any scientific laboratory to help us out.  We initially focused on things that changed from last year and also differences between his and my operations.

First, we concentrated on “Varroa, Varroa, Varroa”.   That would be the easy answer, but the facts had to add up to early varroa caused crashes.  

In 2016 Jon used an oxalic vaporizer for mite control. His winter survival in the 2016-2017 winter was about 80%.   In 2017 Jon started using an oxalic (insect) fogger to apply the oxalic acid.  This was one obvious difference. 

Jon reported he had not been seeing any varroa in the burr comb drone cells all summer.  His past experience was to see varroa on many drones when the burr comb was removed.   We looked at several bottom boards and did not see what we would call excessive varroa, but this was a subjective judgement.

In the spring we had both pledged to do mite checks; either by alcohol wash method or powdered sugar rolls.   Here both of us fell down on the job.  A total of one powdered sugar roll was performed by the both of us.  Pretty poor showing on this important task. 

Jon had adopted use of an insect fogger and an oxalic/alcohol solution for mite control as widely seen on YouTube.  It just takes about 15 seconds to treat each hive.  This is ideal if it is effective.  He did 3 initial weekly treatments in June followed by a knockdown treatment about every second week.  He planned on starting a 2^nd round of the weekly treatments in October after removing the feeders.  That was one big difference between his and my mite control methods.  I used formic acid (MAQS) in mid-August as my primary mite control and did a follow up with oxalic acid vapor in September and October. 

I had been playing with Randy Oliver’s (Scientific Beekeeping) varroa model and looked up the efficacy of oxalic and formic treatments.  The model recommends using an efficacy of 90% for a formic acid treatment and only 15-40% for oxalic acid.  Therefore, it would take multiple ( 3 to 6 ) weekly oxalic treatments for oxalic to equal one formic acid treatment.  Randy’s oxalic data was for either a dribble or heat vaporization.  I queried Randy about oxalic/alcohol, but he had no experience.  He indicated NO ONE had yet compared the effectiveness of oxalic/alcohol to the other methods.  The Scientific Beekeeping website did have a warning from an independent beekeeper/chemist that the oxalic/alcohol solution may break down into a benign compound in the presence of heat (ie. the fogger coil), however, a comparative test or chemical analysis had not been done.

Out of curiosity Jon and I performed a side by side comparison of the acidity levels of MAQS, oxalic/alcohol, oxalic/water (dribble), and oxalic/water vaporized.  As mixed all had a similar acidity level (pH) of 2; a relatively strong acid.  We then went further and applied each into a cardboard box to simulate a hive.  Here the acid levels were lower.  pH levels of 4 to 5 (relatively weak acids) were seen.  But the oxalic/alcohol compared favorably will the MAQS.  No obvious smoking gun here.   However, we did notice during the cardboard box test that the fogger was violently ejecting the vapor (as compared to the vaporizer).   A large portion of the fog was escaping the box when using the fogger.   We agreed to take an additional look at this over a concern that a major portion of the oxalic acid may be being lost to the outside thus lowering the oxalic acid effectiveness further. 

One item of interest we discovered was that although oxalic acid is noted to be less detrimental to queens than formic acid treatments (approx. 3% vs 5% queen loss per application) the cumulative effect over time could be harmful.   For example, 6 applications of oxalic over the summer could result in an 18% queen loss due to the cumulative losses.   This is not associated with Jon’s problem, but this is something to keep in mind when planning your mite control methods.

After all this discussion about varroa and varroa treatments it should be said that a varroa related hive crash is unlikely to occur in the September/October time frame.  Varroa levels should have not had sufficient time to build up to a deadly level if the oxalic/alcohol fog was doing it’s job.    This is especially true for a new package bee colony of which Jon had about five.  If I was using Randy Oliver’s varroa model correctly (a big IF) and assuming a May 1^st start date those five hives would not have had sufficient time for the varroa population to build up to a crash level.   There is also the possibility that Jon’s overwintered hives had relatively high mite levels that in conjunction with the lower effectiveness of the oxalic acid treatments could have resulted in a more rapid mite build up.

Jon had built a bunch of new syrup feeders for use this fall with plastic bottoms.  That was something definitely different.  But that lead fell through.  Jon had hives losses with both old wood bottomed and the new plastic bottomed feeders.  Also, his neighbor’s bees were OK and the neighbor had used two of Jon's new feeders. 

Could Jon’s sugar supply have been contaminated?  Both Jon and I have been using salvaged sugar from a bakery for the last two years.  My bees are doing fine so we tend to discount this possibility.

Could the bees have been hit by a pesticide?  Unfortunately, we have no way of determining this.  The loss did occur in late summer/early fall which is an unlikely time for a pesticide to be used.   Are bees susceptible to other poisoning?  We talked with one neighbor and he had NOT had a hive die-off.  As a point of reference that neighbor had used MAQS for mite control.  The second neighbor's bees were also OK.  Therefore, we tend to rule out a pesticide poisoning incident.

So next we come to the dreaded viruses and bacteria.   Jon had not been seeing any signs of Deformed Wing Virus all summer; ie deformed wings on bees or bees with stunted abdomens.  In addition, the mite load did not seem excessive so DWV is unlikely to have taken hold.   Plus DWV usually makes itself felt in mid-winter when the hive succumbs to the virus. 

A Nosema Ceranae infection is a distinct possibility.  Its symptoms match those of CCD.  Again, we have no method of determining if this was a Nosema Ceranae outbreak.  As for other viruses or bacteria we really have no way to assess the hive for these.  

My hives are spread over a large area in clusters of about 10 hives each.  Jon hives are all in one area maybe making them more susceptible to a communicable disease or virus. 

The odd thing is that all hives in Jon’s apiary are exhibiting the same symptoms.  They seem to have either absconded or all hives stopped successfully raising brood at approximately the same time and 6 weeks later there were no bees left in the hive.   With the hives empty of bees in early October that means the hives stopped having emerging brood in late August and queens stopped laying in early August or no larvae surviving since early August.  Neither of which seem plausible.  Also Jon was still successfully raising queens in early August.  Some of my hives were still full of capped brood in mid-September.   So the remaining option is that the bees in the hives absconded.  

To date, the entire episode remains a big mystery which we will likely not conclusively solve.  Not being one to give up easily Jon is planning on what precautions or modifications to his beekeeping methods to take next spring. 

A.      We both plan to renew our pledge to take periodic mite population samples throughout the summer.  

B.      To answer the oxalic/alcohol versus oxalic vapor questions we plan to run two side by side comparison of both methods.   One will be done in dummy hives and simply compare the amount of oxalic deposited in each hive by the two methods.  The second will be more long term and actually compare mite drops between the two methods. 

C.      Jon is considering adding MAQS to his arsenal in the battle with varroa.

D.      Jon is considering dividing his hives between two (?) locations to potentially prevent drifting and varroa and virus transfer. 

So our recommendation for all beekeepers wanting to avoid a similar story is to monitor mite levels both before and after performing your mite control in the spring and late summer.  Then you will personally know that your mite control method is actually working.