Varroa? No problem – Meet the Asian honeybee

The European honeybee and Asian honeybee are very much alike. With an untrained eye one would not be able to spot a difference. However, while European honeybee colonies are getting devastated by varroa, their Asian counterparts have been living with varroa mites for centuries. Troubles started when European honeybees were moved in and out Asia for apiculture, as this allowed varroa mites to infest European honeybees. How did this happen and why are Asian honeybees so much more efficient in dealing with varroa? And lastly, if the Asian bees are so good in dealing with varroa, why are they not used by beekeepers in Europe anyways?

These, in essence, simple questions are not answered so easily. First, we need to take a look at Asian honeybees (or Apis cerana) and how they deal with the varroa mite. Then we can delve into the special (and dangerous) relationship these bees have with each other and the consequences for beekeeping.

The Asian honeybee can be divided into 6 different groups. In general, they are a bit smaller then European honeybees and have brighter abdominal stripes.
The Asian honeybee can be divided into 6 different groups. In general, they are a bit smaller then European honeybees and have brighter abdominal stripes.

The Asian honeybee

The Asian honeybee is logically found throughout South and Southeast Asia and lives in various climates, such as tropical rain forests, steppes and the lower parts of the Himalaya’s. They are perfectly equipped to live on their own in the wild, but can also be domesticated.

Just like European honeybees, they form colonies and build nests consisting of multiple combs. Their colony can be divided into 3 castes: queen, workers and drones. The workers will maintain the colony by caring for the brood and collecting nectar and pollen, while the queen and the drones are responsible for the reproduction. Sounds pretty familiar right? Asian and European honeybees are in fact so similar that for a while, scientist debated whether they were the same species. However, they are not able to mate together and these days, they are believed to be distinct species which have developed independently from each other for over 2 million years [1].

What makes Asian honeybees different?

First of all, Asian honeybees can be divided into different sub species, as can be seen in Figure 1. All these species have (just like every animal) adapted to their specific environment [2]. For example, the Himalayan bees are very resistant against cold temperatures and can live at altitudes as high as 3500 metres above sea level [3].

Figure 1, The different groups (or Morphoclusters) of the Asian honeybee (or Apis cerana) [2].
Figure 1, The different groups (or Morphoclusters) of the Asian honeybee (or Apis cerana) [2].

Generally, Asian honeybees do not have to survive a long and harsh winter, like most European honeybees. Much of the habitat of the Asian honeybee is closer located to the equator, which means that temperatures fluctuate less during the different seasons.

Because of this, Asian honeybees do not build up a massive food reserve for the winter. Such a large storage of honey would only make their colonies more attractive to be raided by predators. Further, their colonies are much smaller. European honeybees can grow colonies up to 50,000 bees while most Asian honeybee colonies consist of only 6000-7000 bees. These smaller colonies are much more flexible. If they feel like there is not enough nectar and pollen around anymore, Asian honeybees simply leave with the entire colony. This behavior is called «absconding» and allows the bees to migrate whenever needed [4]. In addition, Asian honeybees also swarm more often than European bees, as this is necessary to keep the colonies small and flexible.

Over time, Asian honeybees have co-evolved with various predators, like hornets. Hornets can be very dangerous for the bees, as the stingers of the bees are often insufficient to fight them off. However, Asian honeybees have developed a different tactic. They let a hornet approach near the hive entrance (sometimes they even allow the hornet to enter the hive), then they quickly emerge and surround the hornet, completely covering and trapping it! By moving their flight muscles, they generate heat and cook the hornet trapped inside to death. With this «balling» behavior, Asian honeybees can kill various predators and even the «Asian Giant Hornet» (as the name implies this a huge insect, three times as big as a honeybee). Further, it is assumed that, the bees can also give hornets a warning by shaking their bodies. This signal lets the hornet know they are spotted and they will back off [5].

Asian honeybees can «cook» a hornet by heating up to 47-48 °C.

Asian honeybees and the varroa mite

The Asian honeybees have over time developed various defense mechanism against varroa, namely «hygienic» and «grooming» behavior. These make sure that the varroa is controlled to such a level that is does not harm the colony too much. However, Asian honeybee colonies are never totally free of varroa, both species have co-evolved with each other for ages and kept each other in balance.

Hygienic behavior

Asian honeybees are excellent cleaners, worker bees who pass by worker brood can sense when a cell is infested by mites. Asian honeybees can even sense varroa in capped brood cells. They will reopen the cell and remove the larva, now the mites will be unable to reproduce. It is assumed that Asian honeybees detect the mites by smelling them. Asian honeybees have a better olfactory sensitivity compared with European honeybees [6].

When it comes to drone brood, the workers act a little different. A drone cell in an Asian honeybee colony has a little hole in it. Instead of removing infested drone larva, the workers will let lots of mite enter the cell creating a «varroa trap». They seal the cell with a little wax and let the highly infested drone larva die, together with lots of mites [7].

Varroa mites try to mimic the scent of the colony to evade detection [8], however this is more likely to succeed with species with a less developed smell, such as European honeybees.

Grooming

Another behavior to limit the damage done by varroa mites is grooming. Here, workers will remove varroa mites from the bodies of other bees. Usually when a varroa mite hops onto the body of a worker, the worker is not able to remove the mite herself. The mite´s flat shape and suckers on its feet give these parasite a tight grip on the bees bodies. Other workers can however, bite the mite and in particular its feets so it loses grip of the bee.

Although both Asian and European bees display this behavior, Asian bees due this more often and also more rigorous. When a mite proves difficult to remove, more workers are called in to help. It was shown that 4 workers could be busy removing a single mite of one other worker [9].

Asian honeybee and the spread of varroa

Varroa destructor has historically lived with Asian honeybees species in continental Asia. Because of this, Asian honeybees have developed several defense mechanisms against varroa, in contrast to their European counterparts. Troubles began 50 Years ago when European honeybee colonies where moved in and out of Asia by humans for apicultural reasons [10]. European honeybees produce more honey which caused some to experiment with European honeybees in Asia. This sounds like a pretty silly idea in hindsight, and yes, lots of our troubles with varroa today could have been avoided. However, introducing a new honeybee species for apiculture was pretty common. In fact, the European honeybee can now be found on every continent (except Antarctica). The European honeybee is native to Africa, Europe and the Middle East and was introduced by humans to the Americas, Australia, New Zealand and also Asia [11]. Today the dangers of introducing species to new environments are better understood and the varroa is a sad example of this.

European honeybees are also kept for apiculture in Asia. However, protecting from Varroa and local predators like hornets is difficult and expensive. Although the Asian honeybee produces less honey, because of their resistance against varroa and local predators, they require much less management in Asia.
European honeybees are also kept for apiculture in Asia. However, protecting from Varroa and local predators like hornets is difficult and expensive. Although the Asian honeybee produces less honey, because of their resistance against varroa and local predators, they require much less management in Asia.

The moving of honeybees in and out Asia allowed the varroa destructor to spread onto European honeybees. In the 1975 varroa destructor was found in European eastern Russia, by the late 1980s the mite was present in most of Europe. On the American continent varroa was initially found in South America in the 1970s and spread northwards to the U.S. As of now, only Australia seems to be free from varroa. However some Asian honeybees are present in northern Australia, more specifically in the region of Cairns[4]. Authorities fear that Asian honeybees might spread varroa throughout the continent.

Why can’t Asian honeybees replace endangered European honeybees?

The devastating effects of varroa are a prime example that one cannot simply bring in a new species to a different environment. In areas where different honeybee species exist, they are bound to interact. For example in times of scarcity honeybees will resort to robbing honey from other colonies, no matter which particular specie [12].

Just as the varroa mite is devastating for European honeybees, European honeybees also transmit diseases unknown to Asian honeybees. For example, in the 1990s 90% of the Asian honeybees population were wiped out by the Thai Sac Brood Virus, in southern India. Also other diseases which are common by European honeybees, such as American Foulbrood [13] or Israeli Acute Paralysis Virus [14] are very dangerous for Asian honeybees.

The exchange of diseases between honeybees from different habitats is a good reason to keep the species separate. This is why many governments also prohibit the import of any specie (not just bees) which are not native to the environment. On top of that, some countries have a good reason to be very restrictive in the import and export of beeswax or apiculture products. However, the better developed defense mechanisms of the Asian honeybee can give useful insights in how European bees could deal with varroa in the future. Various research and breeding projects can benefit from a better understanding of this interesting bee.

Literature

[1] Crane, E. (2009). Apis Species: (Honey Bees). In Encyclopedia of Insects (31-32). Academic Press.

[2] Radloff, Sarah E.; Hepburn, Colleen; Randall Hepburn, H.; Fuchs, Stefan; Hadisoesilo, Soesilawati; Tan, Ken; Engel, Michael S.; Kuznetsov, Viktor (2010). Population structure and classification of Apis cerana. Apidologie. 41 (6): 589–601.

[3] Pudasaini, R. (2010). Indigenous Knowledge and Practices of Beekeeping with Apis cerana in Nepal. Journal of Apiculture 33(2): 71-76.

[4] Koetz, A. (2013). Ecology, behaviour and control of Apis cerana with a focus on relevance to the Australian incursion. Insects, 4(4), 558-592.

[5] Tan, K., Wang, Z., Li, H., Yang, S., Hu, Z., Kastberger, G., & Oldroyd, B. P. (2012). An ‘I see you’prey–predator signal between the Asian honeybee, Apis cerana, and the hornet, Vespa velutina. Animal Behaviour, 83(4), 879-882.

[6] Lin, Z., Page, P., Li, L., Qin, Y., Zhang, Y., Hu, F., … & Dietemann, V. (2016). Go east for better honey bee health: Apis cerana is faster at hygienic behavior than A. mellifera. PloS one, 11(9).

[7] Boecking, O. (1999). Sealing up and non-removal of diseased and Varroa jacobsoni infested drone brood cells is part of the hygienic behaviour in Apis cerana. Journal of Apicultural Research, 38(3-4), 159-168.

[8] Kather, R., Drijfhout, F. P. & Martin, S. J. Evidence for colony-specific differences in chemical mimicry in the parasitic mite Varroa destructor. Chemoecology 25, 215-222.

[9] Pritchard, D. J. (2016). Grooming by honey bees as a component of varroa resistant behavior. Journal of Apicultural Research, 55(1), 38-48.

[10] Solignac, M., Cornuet, J. M., Vautrin, D., Le Conte, Y., Anderson, D., Evans, J., … & Navajas, M. (2005). The invasive Korea and Japan types of Varroa destructor, ectoparasitic mites of the Western honeybee (Apis mellifera), are two partly isolated clones. Proceedings of the Royal Society B: Biological Sciences, 272(1561), 411-419.

[11] Winston, M.; Dropkin, J.; Taylor, O. (1981). Demography and life history characteristics of two honey bee races (Apis mellifera). Oecologia. 48 (3): 407–413. 

[12] Kojima Y., Toki T., Morimoto T., Yoshiyama M., Kimura K., Kadowaki T. (2011). Infestation of Japanese native honey bees by tracheal mite and virus from non-native European honey bees in Japan. Microb. Ecol. 62:895–906.

[13] Chen, Y. W., Wang, C. H., An, J., & Kai-Kuang, H. (2000). Susceptibility of the Asian honey bee, Apis cerana, to American foulbrood, Paenibacillus larvae larvae. Journal of Apicultural Research, 39(3-4), 169-175.

[14] Theisen-Jones, H., & Bienefeld, K. (2016). The Asian honey bee (Apis cerana) is significantly in decline. Bee World, 93(4), 90-97.

Vatorex, Felix Poelsma
17 September, 2019
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