Sacbrood Virus: Calling the Inspector.

Another Busy Week.

At last we have a few days without a single rain shower and the sun is out. The super frames are being capped at last and the bees have discovered the Himalayan balsam down at the river. Though it has been in flower for 2 weeks, this is the first sighting of the distinctive white pollen on bee thoraces from when they pushed in below the anthers to reach the nectaries of the flowers.

I check my diary and note that they discovered it on exactly the same day last year. A local bonus this year has been access to a field of buckwheat and phacelia sown by the farmer as a pollinator friendly field margin. Phacelia pollen is a glorious bright periwinkle blue colour. I smell heather nectar being processed into honey. Something I was hoping to avoid having to extract alongside lime honey, but I’m thankful to be able to harvest anything and still leave the bees with their own stores for winter.

Eucryphia glutinosa.

In the garden, the leatherwood (Eucryphia) is covered in subtly scented flowers that have attracted a frenzy of foragers of many insects species. A friend took me out for lunch at Cawdor castle this week and we enjoyed watching insects on the richly coloured flower beds there. We both agreed that we haven’t seen as many butterflies this year and we only spotted a couple of peacocks in the castle gardens.

I run out in a hurry and forget to take my wellies when I help a friend try to work out why a colony has become super defensive. I am wearing my bee suit (no dress today,Liz C!) but there’s an inch of ankle showing. The stings are so painful and I borrow my friend’s wife’s wellies. I get stung on the sole of one foot (the softest part) as I change footwear and I feel the pain for a day as I walk– a reminder of my negligence.

Defensive Colony.

Defensiveness is a subject for next week, but this colony was not queenless as I had intially thought might have caused the anger. It had no stores in the brood chamber and very little in the super. At this time of year, the colony goal is to amass stores above the brood nest and when this is not happening they are insecure and defensive. There is not time to collect enough now as we reach the end of the season. Some colonies storing for winter are not unlike some defensive human shoppers driven to aggression by some insecurity which leads to bulk buying when they think there will be a shortage in the supermarkets.

The additional problem in this apiary is neighbours objecting to living next door to bees. We put on a block of fondant which reduces the risk of robbing in the apiary, and also the need to disturb them to top up syrup. This colony can be left alone till the time is right to remove them to a newly prepared isolated out apiary.

Calling for the Bee Inspector.

I’m helping Cynthia prepare her distillery colonies for winter when I notice a brood disease in one of them. What I see first is perforated cappings, and on examination, with a match stick (I’ve left my forceps at home!), I notice brown gooey material which ropes slightly but not as much as 2cm. Initially, I think/hope it might be the start of chalkbrood but that is usually white/grey moist material and not caramel brown like this. There is one white Chinese slipper type larva but I am not going to take the risk of diagnosing this myself and so we agree to call out our local bee inspector who will take a sample to exclude American foulbrood which could be present. The matchsticks are disposed of in the smoker.

We go up to my house and call the inspector. The message on the answering machine of the Inverness office doesn’t convince me that we might get a reply soon, so I call the Government head office in Edinburgh and within 3 hours we have an inspector arriving at the distillery.

Water-loving purple loosestrife with the copper distillery vats in the background.

We arrive early to meet Claire Gill, Deputy Lead Bee Inspector for Scotland, who is on her way home from Perth to Dornoch. The weather in Perth is too bad to inspect colonies down there as it is raining and 7degrees Celsius! Our luck is in today. We walk round the grounds till we see her approach.

Cynthia looking relaxed though we are both on edge.

Claire has no difficulty identifying us and smiles as her car draws up. She is friendly and efficient and prepares for the inspection by getting the paperwork done first. She makes up a bucket of washing soda for hive tools and gloved hands. She sprays her wellies with Vircon to disinfect them and we help her carry things over to the apiary. We have a challenge today because gas pipes are being installed and deep channels have been excavated meaning we have to jump across a wide gap. Luckily the digger driver has gone. We anticipate angry bees after an inspection only a few hours previously.

Claire’s strategy is to inspect the suspicious colony last. She checks them all with a gentle efficiency and we are all relieved that the bees take the disturbance so well. As discussed in a previous blog,most of the bees must be shaken from the frames.

Did you spot the offending cells in this photo? The queen has laid up the cells in the middle but most of the sealed cells have diseased larvae.

You can see why it is called sacbrood, the larvae fail to pupate and what you see is a sac of ecdysial fluid. This larva is probably going to disintegrate and become a gooey brown thick material, not unlike what happens with AFB but it will only rope about 1cm. What that means is when you poke a matchstick into the cell the material forms a gelatinous mucus-like thread which breaks off when it is about 1cm long in this case.

The sample collected is about to be placed in an Eppendorf tube to be sent to the laboratory in Edinburgh.
A dried up infected larva.

Claire is certain that this is a case of sacbrood virus and not AFB but she takes a sample just to be sure. Bee inspectors no longer carry lateral flow tests which are very expensive and not always accurate. They go out of date very quickly and it is beyond my comprehension why some hobby beekeepers would buy them, but they do.

We discuss management because this common virus is transmitted by varroa but it is too late for a shook swarm which would have been a good treatment so Cynthia will use formic acid (Mite Away Quick Strips).

We breathe a sigh of relief. I invite Claire home for a cup of tea but Cynthia has to prepare for a bridge party, as in cards!

About Sacbrood Virus.

Like deformed wing virus (DWV), sacbrood is classed as an RNA iflaviridae virus and the virus particle is about 30 nm in diameter. As with DWV, it is transmitted by varroa. It is common worldwide and not considered to be highly pathogenic and it occurs in spring and summer. However, in autumn is it often seen alongside heavy varroa infestations.

The infection spreads via royal jelly and can be found in stored pollen and honey and the oral route is the principal one.

It is not considered to be a problem for adult bees but they may be responsible for spreading the virus via brood food. Interestingly, the western honey bee, Apis mellifera, copes with this disease and removes infected larvae but it is a lethal disease for the Asian, Apis cerana, honey bee and their colonies are easily killed by sacbrood.

Worker, queen and drone larvae may become infected and they are most sensitive to the virus at 2 days of age. The infected larva continues to develop until the cell is capped but this is when it starts to die. Because it is unable to shed its skin during the first moult, it cannot progress and the ecdysial fluid, which should dissolve the outer cuticle, builds up under it causing a sac.

The larval colour changes from pearly white to yellow and, if not cleaned out by cleaner bees, they decompose becoming sticky and brown and can rope in a thread of up to 1cm long. The infected larvae can also dry out into black Chinese slipper shapes with the head being much darker as you can see from the photograph I took.

Impact on Colony.

There maybe a colony imbalance as a result of infection whereby infected adults become foragers earlier than otherwise and they tend to collect nectar rather than eat pollen . The individual bee life span shortens and the colony might become weak. During the spring build up when there is a peak in brood production there may not be enough nurse bees to care for them all and the virus, which is lying dormant, can cause symptoms.

Contributing factors are: lack of food, population imbalance, confined to hive for long periods, and poisoning is also thought to be an associated problem.


Giving a strong colony plenty of space helps as they are less densely crowded in the hive. An infected colony should have its brood frames removed and a shook swarm is carried out if the season it suitable. The old contaminated equipment should be disinfected and old comb destroyed. Avoid starvation and consider feeding and pollen supplements. Some suggest that the colony should be destroyed if more than 20% of its brood is affected. Re queening is also worth trying.

4 thoughts on “Sacbrood Virus: Calling the Inspector.”

  1. Wow, just shows you how careful and observant we have to be when inspecting our colonies. Thanks for the revision, Ann.

  2. Thank you, Ann, for the detailed information about sacbrood virus. Over here in New York State, I rarely see it in a strong colony, but it does pop up in weak ones from time to time. I think of it as a “stress disease.” Your suggestion of providing an infected colony with some sugar syrup and pollen supplement makes much sense to me.

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