"  You seem to ascribe your empty cells to EFB.  Could not the cause also be attributed to other causes such as the
 presence of varroa or other diseases?"

There are lots of reasons for empty cells.  But, when you have requeened or had the hive supercede once or twice and gone two months with hardly any sealed brood I think you can eliminate queen issues.  Particularly when you see an excellent pattern of eggs and new larva that simply go away by the time they are a few days old.  Then you treat that hive with antibiotics and four or five days later see an excellent pattern of sealed brood.   No mite counts were done prior to treatment but those hives later have mite counts of zero to two/100 bees.  With my early spring mite treatment program plus the Minnesota Hygienic queens I run you can not find many mites in my place in any colony most of the summer.  The last two years they have been so low I have not even done a fall treatment for mites, althou on a very strong fall colony before the current years bees die off I am coming to the conclusion I should do a fall treatment at even one or two mites per 100 bees.  I am seeing too many strong fall hives among my weakest by spring or even dead.

For the last three years I have seen occasional nucs like this every summer.  Every single one has responded dramatically within days to antibiotic treatment, probably a total of ten nucs so far.  I do no prophylactic antibiotics of any kind, nor have I used them on even a single hive with other symptoms.  I showed one to our local bee inspector and he declared the queen too new to have sealed brood althou she had been laying ten days.  He was sure it was not a disease in spite of the fact there was almost no larva over two days old at the time and older larva were very scattered.  Two months later after two new queens and few bees left I treated with antibiotics and had sealed brood in a few days.  I have not had a single occurrence of the symptoms showing up again after three treatments according to label directions.  I have also not seen dead sealed brood.

The text book symptoms for EFB are larva laying at an odd angle in the bottom of the cell and turning yellow.  I have only seen this on one single long term case and even then had to look in thousands of cells to see two or three examples.  That was my reason to treat with antibiotics the first time.  That was also the nuc on the third queen with hardly any bees left.

That does not prove EFB but it sure does prove a bacterial problem in my opinion.  So, if it is not EFB give me a new name.  I can not think I am the only person who sees these symptoms.  It is also well proven that MH queens are useless against EFB in challenge tests.

Dick
  

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