Bee Covid?!

Just kidding bees don't have covid but they can get viruses too. You might have heard that covid-19 is an RNA virus. RNA is similar to DNA but it is a single strand unlike DNA which is a helix of two joined strands. RNA also differs in one of the four base pairs thymine, in RNA it is uracil. In our cells RNA is made by copying our DNA and used to make proteins that make up us. However in humans information is not stored as RNA for long because its single strand it is less well protected from damage and mutagenic agents. Indeed RNA experiences mutation at very high rate which means RNA viruses mutate a lot and are made up of many different strains much like covid-19.

In honey bees there is a particularly problematic RNA virus known as deformed wing virus. Naturally, the name deformed wing virus comes from the observation of highly infected individuals with misshapen and unusable wings (like in the image below).

However, not all highly infected bees have deformed wings and an arguably more important affect is that the virus shortens the lifespan of honey bees that are infected as pupae by around two thirds. This means that in an infected colony many members will die young making it vulnerable to collapse. In the northern hemisphere this is particularly more likely over winter when the colony needs the long lived winter bees to keep the colony warm and rebuild after winter. (Winter bees are worker bees that have enhanced fat stores and can live for many months)

Deformed wing virus has spread pretty much world wide and has been in honey bees for a long time. It used to not cause much damage as the amount in hives was tiny. However this all changed when the Varroa mite spread to Western honeybees. The Varroa mite is very good at spreading the virus. It does so when it feeds on the pupae and adult bees. Varroa meant that the amount of deformed wing virus in colonies increased dramatically. The diversity of the virus also decreased because only certain strains could survive the mode of spread by the mite.

There are now three recorded master strains of deformed wing virus which are called DWV-A, DWV-B and DWV-C. The virus does still mutate very rapidly and so these strains constantly mutate. But because the three major strains are well adapted to the host they are not lost. In fact deformed wing virus forms what is called a quasispecies. This is where the level of mutation means there is a constantly changing swarm of viral variants. However despite the changes the master strains a, b and c remain present. Currently strains A and B dominate most landscapes and c is relatively rare. Work is still ongoing to discover which is the most virulent (harmful) strain.

Could we vaccinate bees?

Someone once asked me this and I have to say that it is probably not possible. Bees don't have the same immune system as us and don't have antibodies as such. These are what allow our body to 'remember' and respond to viruses. Additionally it would be rather expensive and tiresome to do this for all 10,000+ colony members!

Honeybees do have a method to destroy viruses which is called RNA interference in which an enzyme is used to cut up viral RNA. There have been studies showing that this can be used to destroy deformed wing virus RNA however the efficacy is still disputed.

The best way we have to control deformed wing virus so far is simply to control mite populations. This is particularly important to do in summer-autumn before winter so that the winter bees are healthy. Many need to use chemicals to do this however there have been increasing reports in bees that are resistant to the mite and so require no control. But that's a big topic and something I want to talk about in a later post