EFB Picture Diary - Part III
The Bee Inspector called on us today, to check up on the colonies following last year’s EFB outbreak.
Since I had shook swarmed the four previously healthy colonies, there were only low numbers of larvae to be seen in them and they will all need re-inspection at a later date, but as of today they appeared well. Interestingly, Queen Peony’s colony appear to be undergoing supercedure, i.e., a daughter queen is being reared for succession while the old queen continues her “reign” in the same colony, the two queens overlapping for a time before the old queen is finally disposed of by her no-longer-loyal subjects. It’s only 10 days since the shook swarm and they already have a capped queen cell, which indicates they began the supercedure process the day after being transferred to the new hive. The Inspector thought the bees had probably pinned the blame for the shook swarm on Queen Peony and decided to oust her as a result.
Healthy colonies are always inspected before diseased/suspected ones (insofar as that can be predicted in advance), to minimise the risk of disease transfer by beekeeper.
So Queen Mab’s colony were inspected last. And now we come to the sad news, which is that despite antibiotic treatment at the end of last summer, this colony still has EFB.
The photos above show brood in Queen Mab’s colony. If you know what you are looking for, you can see diseased larvae there (click to embiggen). If you don’t, you can consult the images below.
The Inspector has shaken the frame to dislodge most of the bees, exposing the brood comb. Some nurse bees remain on the comb, attempting to cover and warm the brood (it was a chilly morning, too cold for beekeeping under normal circumstances). Many of the open cells (left side of the first picture) contain a white C-shaped larva at the bottom. Nurse bees are checking on the young larvae in the open cells - you can see their heads looking down into the cells and their bottoms sticking up. The cells of the older larvae have been capped with biscuit-coloured, lightly domed toppings of porous wax. Inside these capped cells, the brood are pupating into adult worker bees which will eventually emerge through the caps, antennae waving. The capped brood looks normal except that it is peppered with empty cells. A healthy queen lays one egg per cell in a regular array, producing a solid plate of brood which are all at about the same age and should therefore all be capped at the same time. The many empty cells that appear within the pictured plates of capped brood are where the nurse bees have found dead or dying larvae and have removed them. They do not cap the empty cell, and may instead use it as a temporary store for pollen or nectar. The arrows point to some diseased larvae which are still present.
The Inspector took one of these diseased larvae to run the EFB diagnostic test.
It’s positive, which isn’t a surprise after seeing the brood.
But this means a death sentence for Queen Mab and her colony.
I had previously understood the plan to be a 2-part treatment of (i) antibiotics and (ii) shook swarm, but it turns out that the National Bee Unit only proceeds with the shook swarm if a colony responds to the antibiotic treatment. For a colony which still shows disease after antibiotics, destruction is the only permitted “cure”.
I will therefore be using petrol in the apiary again. Queen Mab’s colony are ordered to be dead within 10 days of today.
According to the Bee Inspector, about 1 in 4 colonies still show visible disease after oxytetracycline treatment for EFB. It may be that they are infected with a more resistant or virulent strain.
Which brings me to the outcome of the strain testing performed on the EFB samples that were sent off to DEFRA’s lab last year, to try to identify a match with other EFB cases and provide information on how the disease might have spread. This is a picture diary, so let me post the DNA test results here:
OK it’s not the results; it’s a representative artwork by me. DEFRA’s lab had a technical problem and weren’t able to run the DNA tests. The Bee Inspector will be sending them the new sample from today, so let’s hope that we will be able to get strain information from that one.
Continued in Part IV…