Bees Commit Suicide to Save Colony From Parasites

Bees Commit Suicide to Save Colony From Parasites
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When a virus infects a cell inside a living organism, it quickly moves to hijack its new host. Once commandeered, the cell will become a helpless pawn in the virus' nefarious mission to replicate and spread throughout the body. That's why the cell quickly takes a drastic move: it commits suicide. Rather than linger on as a puppet for the invading virus, the cell disintegrates in a process called apoptosis, sacrificing itself for the sake of the whole organism.

According to new research published in Scientific Reports, the Eastern honey bee, Apis cerana, does almost exactly the same thing!

A bee colony is much more than a mere collection of individual organisms; it is an organism itself. In fact, scientists have taken to calling colonies of socially-organized insects (like bees or ants) "superorganisms." In this manner of looking at things, individual bees are comparable to the cells inside your body. And just like the cells in your body can be infected with viruses, the bees in a colony can also be infected... with microscopic parasites.

For years, the Eastern honeybee has been besieged by one such parasite, ominously named Varroa destructor. Within an infested colony, the mites feed on the blood of individual bees and spread disease. But the Eastern honey bee has been fighting back. While colonies once died in couple years, they are now resisting and even surviving. This has prompted the parasite to switch its primary host to the Western honey bee, A. mellifera, the most common honey bee species worldwide. The mites are now significantly contributing to the Colony Collapse Disorder plaguing the species.

According to the new study, the Eastern honey bee's resistance to V. destructor seems to be fueled by what the researchers have dubbed "social apoptosis." Rather than struggle to survive when infested with mites, worker larvae of the Eastern honey bee die much more easily, preventing the mites' spread. The researchers turned up the finding after infesting the larvae of five colonies of Eastern honey bees and six colonies of Western honey bees with V. destructor. While Western honey bee larvae developed normally, Eastern honey bee larvae developed much more slowly, and often didn't develop at all (see example above). (Below figure: Eastern honey bees (A. cerana) take much longer to develop than Western honey bees (A. melifera).)

"The observed social apoptosis is most likely a fundamental defence mechanism of social insect colonies to combat diseases," the researchers write.

"Our counterintuitive result shows that susceptible individuals can benefit the superorganism, which goes against the common assumption that ‘strong’ elements of a social entity are required to ensure group survival."

The authors suggest that breeding Western honey bees that demonstrate the behavior could help to combat Colony Collapse Disorder. Between 2007 and 2013, almost 10 million bee hives have been lost to the disorder.

Source: Page, P. et al. Social apoptosis in honey bee superorganisms. Sci. Rep. 6, 27210; doi: 10.1038/srep27210 (2016)

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