Tag Archives: honeybees

Bees: How do they Combat Disease?

A honeybee hive sick with disease can spell the end of a colony. Recent research has shown bees can use vaccinations and nurse one another to protect themselves from and prevent certain diseases. But how exactly do they do it?

Vaccinations

Honeybees live in huge colonies that co-operatively rear brood (developing eggs and larvae), so must find some way of protecting the next generation against disease. To do this, the workers actually naturally immunize their young against certain diseases which they might encounter. The findings of a recent paper, published in the journal PLOS Pathogens, finally reveal how the important immune-signal protein vitellogenin works to do this.

It was found foraging workers pick up and bring back contaminated pollen and nectar to the hive, and workers create royal jelly using it. The bacteria picked up from the environment persists in the jelly, and is then fed exclusively to the queen. The pathogens are digested in the queen’s gut and stored in the queen’s fat body (an organ similar to a liver). Fragments of the bacteria are then ‘carried’ by vitellogenin, taken via the blood to developing eggs inside the queen. These young are now immunized, all without taking a step outside their hexagonal brood cell.

Now that we know how bees immunize their young against infection, scientists can work on synthesizing a vaccine to prevent commercial bee colonies from becoming infected with disease- possibly aiding the fight against the crisis of colony collapse disorder (CCD).

But not all diseases in bees can be fought with immunity inherited from a parent. So how else do honeybees fight infection?

Nursing

Much like communist societies, honeybee hives divide up the hugely varied workload between different ‘castes’ of the colony (workers, drones and queen), and further divide workers into roles based on their size and age. Older, more experienced workers may be more likely to forage for the colony, and act as guard bees (they have actually been found to patrol the entrance the hive!). Younger, more naive workers however are usually more suited to nursing duties, which include feeding and tending to the queen and brood, as well as medical specialists which provide sick workers with anti-biotic laced honey.

A recent study, published in Behavioural Ecology and Sociobiology, gave nurse bees infected with a Nosema ceranae parasite a choice of honey from different plants. Bees with a higher level of infection tended to eat more sunflower honey, which contains the most antimicrobial activity. It also reduced the level of infection in the bees by 7%. A separate study suggests different honeys are effective against different diseases the bees may encounter. For example linden honey was better at fighter off a an infection of European foulbrood whereas sunflower honey was more effective against American foulbrood.

Nurse bees have other medical roles to reduce infection in a hive. For example, they can act as undertakers and remove the corpses of dead bees from the colony, dumping them far from the entrance. This behaviour is used to avoid spreading infections from pathogens and entomopathogenic fungi that proliferate on the bodies of dying insects,

In both of these incredible behaviours, bees can vaccinate and immunize their brood and sister workers by means of medicinal honey and food contaminated with bacteria. But where do these come from in the first place?

Natural Remedies

Floral nectar typically contains plant secondary compounds (those used for defence by the plant) which possess antimicrobial properties. This can be very useful to bees. Before the publishing of a recent study in PLoS One, we knew little more than the fact pollinators can reduce their parasite load by consuming nectar containing compounds such as nicotine.

This recent research has indicated parasitized bumblebees are taking advantage of these plant secondary metabolites in the wild, such as iridoid glycosides, and have a strong preference for visiting flowers that possess them. This quality of bees to self-medicate, by altering their foraging behaviour whilst parasitized, has massive implications for their ability to fight disease

Honeybees have other sources of medicine besides anti-microbial nectar. They have been found to collect resin from plants and incorporate it into their nests, which may help stop fungal parasities from colonizing their hive. (A study showed bees collect more of the resin when infected with fungal spores)

Final word

The fact that honeybees and bumblebees have evolved so many different ways in which to fight disease implies the risk that our wild pollinators face, as well as just how long they have been co-evolving alongside their assailing antagonists. Climate change and other drivers have recently made the problem of disease much worse, and research into this need to be rapid if we are to help our plighted pollinators.

Further Reading

Erler, S., Denner, A., Bobiş, O., Forsgren, E., & Moritz, R. F. (2014). Diversity of honey stores and their impact on pathogenic bacteria of the honeybee, Apis mellifera. Ecology and evolution, 4(20), 3960-3967.

Gherman, B. I., Denner, A., Bobiş, O., Dezmirean, D. S., Mărghitaş, L. A., Schlüns, H., … & Erler, S. (2014). Pathogen-associated self-medication behavior in the honeybee Apis mellifera. Behavioral Ecology and Sociobiology, 68(11), 1777-1784.

Richardson, L. L., Bowers, M. D., & Irwin, R. E. (2015). Nectar chemistry mediates the behavior of parasitized bees: consequences for plant fitness.Ecology.

Salmela, H., Amdam, G. V., & Freitak, D. (2015). Transfer of immunity from mother to offspring is mediated via egg-yolk protein vitellogenin. PLoS Pathog, 11(7), e1005015.

Simone-Finstrom, M. D., & Spivak, M. (2012). Increased resin collection after parasite challenge: a case of self-medication in honey bees. PLoS One,7(3), e34601.

Diseases in bumblebees and honeybees

All species of bumblebee and honeybee have associated diseases and parasites that impact on the health of populations. Emerging infectious diseases (EIDs) are those that pose a risk to human welfare (directly or indirectly) that affect ecosystem service production such as pollination of flowers or health of livestock. But what are these diseases and what are the factors that exacerbate them?

One commonly cited cause for colony collapse disorder (CCD) of the american honeybee (Apis mellifera) is the mite Varroa destructor. Varroa carries and transfers the viruses deformed wing virus (DWV) and acute bee paralysis virus (both implicated in CCD). Affliction with varroa mite also tends to weaken the immune system of honeybees. ‘Hygienic’ colonies of honeybees are able to remove the mites from brood cells and the workers groom themselves to remove the mite and disrupt it’s life cycle- this is a form of ‘resistance’ to the mite.

Other common parasites of honeybees include acarine tracheal mites, nosema spp (fungus that infest intestinal tracts), small hive beetle, wax moths and tropilaelaps (mites). Bacterial diseases include american foulbrood and european foulbrood and fungal diseases include chalkbrood and stonebrood. Honeybees are also susceptible to dysentery (inability to void faeces in flight) and viruses such as chronic and acute paralysis virus, kashmir bee virus, black queen cell virus, deformed wing virus and cloudy wing virus.

Researchers have found that two of these honeybee diseases (DWV and Nosema cerenae) are capable of infecting adult bumblebees. Further field work found that 11% of bumblebees were infected with DWV and 9% with N. cerenae, compared with honeybee infection rates of 35% and 7% respectively. The most likely explanation for the disease incidence in bumblebees is infection by honeybees, but bee-keepers can reduce the spread of disease by regular brood comb changes.  It is thought that ecological traits of these pollinating insects (e.g. overlapping geographic ranges, ecological niches and behaviours) promotes cross-species transmission of RNA viruses. Social behaviour and phylogenetic relatedness of social pollinators is thought to further facilitate transmission within and between hosts.

More recent evidence has suggested that commercial colonies bred for crop pollination and honey production can carry diseases (parasite infections and over 20 viruses) and be a threat to native species. Researchers found that 77% of imported bumblebee hives were contaminated with up to 5 different parasites. There is an urgent need for further research into the health of wild and imported bees and improvement in monitoring and management practices for honeybee and bumblebee colonies

Fürst, M. A., McMahon, D. P., Osborne, J. L., Paxton, R. J., & Brown, M. J. F. (2014). Disease associations between honeybees and bumblebees as a threat to wild pollinators. Nature, 506(7488), 364-366.

Manley, R., Boots, M., & Wilfert, L. (2015). Emerging viral disease risk to pollinating insects: ecological, evolutionary and anthropogenic factors. Journal of Applied Ecology.

Decline of Pollinators could Worsen Global Malnutrition

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Pollinators contribute to about 10% of the economic value of crop production, but the contribution to human nutrition by these pollinators is potentially much higher. This is because pollinators support the sexual reproduction (by transfer of gametes aka pollen) of crops high in essential nutrients that malnourished regions of the world rely on. This suggests that regions already facing food shortages and nutritional deficiencies will suffer particularly hard from the global decline of bees and other pollinators.

Many of the crops dependent on animal vectors to pollinate (instead of wind) are the ones most rich in micronutrients essential for human health. The recent decline of important pollinators, such as the domesticated Western honey bee, Apis mellifera, has lead to concerns on the economic and now nutritional situation of crop production.  Dr Chaplin-Kramer and colleagues set out to assess the importance of pollinators to global health by determining which regions these crops are most critical for and what their micro-nutrient content is.

The research concluded that pollinator decline could affect different regions of the world in entirely different ways. Developed regions such as China, Japan, U.S.A. and Europe relied on natural pollinators for producing crops of high economic value, whereas lesser developed regions such as South Asia, India and sub-Saharan Africa relied on natural pollinators for producing crops of high nutritional value. Chaplin-Kramer and colleagues also mapped out hotspots that relied on 3 essential micro-nutrients; iron, vitamin A and folate. The regions depending most on pollination for nutrition delivery also tend to have high rates of malnutrition and poverty.

The health concerns potentially resulting from this include vitamin A deficiency, which is associated with blindness and increased risk of disease, iron deficiency which causes anaemia and pregnancy complications, and lack of folate that causes folate deficiency anemia. This study has also highlighted that the effects of pollinator decline are much more diverse and widespread than the well-known crop production and income problems. However there are ways for the regions to adapt to changes to pollination services, such as using managed bee colonies to supplement wild populations, switching to alternative nutrition-equivalent crops less reliant on bee pollination and importing nutrient-rich foods from other countries.

Chaplin-Kramer, R., Dombeck, E., Gerber, J., Knuth, K. A., Mueller, N. D., Mueller, M., … & Klein, A. M. (2014). Global malnutrition overlaps with pollinator-dependent micronutrient production. Proceedings of the Royal Society B: Biological Sciences, 281(1794), 20141799.

How do Social Insects make Decisions?

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Using information passed on by others can greatly improve individual fitness, and has been the fundamental mechanism underlying the evolution of social insects such as bees, wasps, ants and termites. However in some situations it is better to ignore social information and for an individual to use its own prior knowledge and experience. So how do these colony-forming insects tailor their reliance on social information for the benefit of the ‘superorganism’? Scientists have recently reviewed the literature and made theories as to the nature of decision making in insects.

Social information is relatively ‘cheap’ to obtain for hymenopteran foragers, because they can bypass the costs associated with exploration and food sources obtained socially are likely to be better quality. In the truly eusocial western honeybee, Apis mellifera, generations overlap so information passed on by the ‘waggle dance’ (movements conveying location and quality of food sources) increases the fitness of that colony. Foraging choice are further refined by chemical cues (pheromone trails) and simply presence of other foragers.

Relying on social information may also incur costs and may not lend an evolutionary advantage. In the case of the ant forager, if she ignores social information she may find a novel food source that will benefit the colony as a whole, whilst a well-used food source is depleted (I.e. exploration produces more up-to-date information). Honeybees that rely on dance information may take time to find a dancer and may need multiple viewing and excursions to find the communicated food source.

A trade-off between these advantages and disadvantages will adjust how often (and what proportion of) social insects rely on social information. All animals tend to display the most profitable information they know, so relying on social information may be more profitable than exploration. For example honeybees only communicate their dance after finding high quality food sources. ‘Social learning strategies’ in animals are genetically determined in response to environmental and social cues. One such approach is the ‘copy if dissatisfied’ strategy, where animals will use social information if their current information is below a fitness ‘threshold’. These optimum social learning strategies can also be acquired (ironically) through social learning.

Grüter, C., & Leadbeater, E. (2014). Insights from insects about adaptive social information use. Trends in ecology & evolution, 29(3), 177-184.