New Research Reveals Complex Varroa Diet.

Varroa on pupa. Photo from Wikkicommons.


After a light blog with the sweet story of honey cakes, it’s time to get back to some serious stuff and turn our attention to the number one challenge in the apiary; Varroa destructor. I’m a member of Humberto Boncristiani’s InsideTheHiveTV Academy and privileged with perks such as attending live some of the interviews that he records with scientists and beekeepers. You can watch some here;

New Research.

Last week, Dr. Olav Rueppell shared some really interesting things about how Varroa and Tropilaelaps mercedesae feed1. Dr.Rueppell  and his colleagues have just expanded the recent work of Dr. Ramsey et al2 and found that the life histories of both parasites and hosts determine the parasite diet which changes through their lives. Quite a fascinating revelation.

In 2019, Dr. Samuel Ramsey shook up the beekeeping world with his discovery that Varroa mainly feed on fat body tissue rather than haemolymph as we had thought for years. You can hear his story here.

Using fluorescent staining, Ramsey demonstrated that Varroa primarily feed on fat body tissue of adult bees. When scientists increased the fat body diet under lab conditions Varroa lived longer and their fertility and reproduction increased. In an adult honey bee, the fat body tissue is mainly situated under the abdominal cuticle, and below the second sternite of the abdominal segment is the most common feeding site with 44.59% of feeding taking place there. There is little if any fat body tissue in larvae.  Varroa probably only feed on pupa during metamorphosis once the cell has been capped. The mother foundress Varroa mite and her offspring feed through one puncture site whereas Tropilaelaps m. feed on multiple sites causing more damage to pupae.

What do Mother Mites Eat?

The Ramsey research didn’t look extensively at foundress mites and what they ate, so Rueppell and colleagues made this the focus of their very recent work. Both Varroa and Tropilaelaps have evolved to utilize honey bees as food sources during their two main life stages which are dispersal and reproduction. The Rueppell study confirmed the breakthrough Ramsey discovery and added another layer. After all, science is dynamic and our knowledge is continually updating.

The most common feeding site of Varroa at the dispersal stage. Photograph Crown Copyright.

We are familiar with the term phoretic and have used it for years to describe how Varroa travel around on adult honey bees, until it is time for them to get inside a brood cell, before it is capped, and begin their reproductive stage. However, the term “phoretic” is not used anymore in science. This is because we now know that Varroa feed on the adult bee at the dispersal stage. Phoretic means, “exploitation of a host exclusively for transport and it specifically excludes exploitation of a host as a food source”. Hence the scientifically correct term “dispersal” is now being used to describe accurately the behaviour of Varroa mites. It is important to know that Tropilaelaps spp. do not feed on adult bees. Interestingly, unlike Varroa, Tropilaelaps don’t need to feed on their host to stimulate egg production (oogenesis). The latter feed purely on pupae and, as we will see soon, they mainly consume haemolymph.

The size and content of fat body tissue varies throughout a honey bee’s life and newly emerged larvae and old forager bees have depleted fat body stores. It is the nurse bees that have the largest stores of fat body tissue; more than any other bee in a colony. At the dispersal stage, Varroa attach themselves to the honey bee abdomen and access fat body tissue through membranes that they puncture.

Different Nutrients at Different Stages.

So, how do scientists know what mites are feeding on at these two development stages? They have analysed wounds and fluids using fluorescent staining and studied the structure and function of proteins (proteomics) and compared these between parasite and host tissue. They have also examined and analysed mite faeces. What they discovered is fascinating and helps us understand this new concept of life-history stage determining diet. When the foundress mite, in her reproductive stage, feeds, she mainly ingests pupal haemolymph which appears to involve amino acid metabolism and the production of proteins. It is worth noting that both parasite and host are at their reproductive stages. When Varroa is at its non-reproductive dispersal stage it needs to feed on fat body tissue to promote lipid metabolism. The host at this stage is also in its non-reproductive state.


Varroa on left with Tropilaelaps right. Photograph Crown Copyright .

What about Tropilaelaps (Tropi)? Well, we don’t yet know so much about this parasite, but Dr. Rueppell confirms that it is expanding its range and it is much worse in Thailand but not so bad in China at the moment. There are currently two species that have the potential to be much more virulent than Varroa. They have a faster life history and the foundress Tropi lays eggs after only 10 hours following cell capping, whereas it is 60 hours for Varroa. Tropi don’t need to feed on adult bees to stimulate egg laying so the foundress only spends 1.3 days in the dispersal stage compared with 4-6 days for Varroa when there is brood present. Tropi have a faster egg-laying rate of an egg every 24 hours compared with one every 30 hours for Varroa.

There is one main difference though and it is that Tropi do not feed on adult bees, whereas we know that Varroa do and that they can survive for several months without brood because they are feeding on adult bee fat body tissue. This means that Tropi may not fare well in countries where there are long broodless periods. However, we still do not know enough about them to make accurate predictions. We don’t even know what viruses they might spread.

Significance for Beekeeping.

So, how does this new research help us in beekeeping? Well, the more we know about an enemy the easier it becomes to find its weak spots and scientists might just find some viruses that will harm Varroa. Meanwhile we can keep up a multifaceted approach using biotechnical methods and promoting hygienic behaviour in honey bees.




2 thoughts on “New Research Reveals Complex Varroa Diet.”

    1. Hello, Stephen. Glad you liked this one and thank you for commenting. The observation hive bees are thriving in the nuc outside the shed. Just waiting till spring really arrives before moving them back indoors. If you are up for helping me install them again it should be a lot easier than it was last year?

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.