How conventional agriculture could make bees less resistant to disease

Beehives close to agricultural land lack the microbial diversity that could help them to fight infection and produce their nutrient-rich food, says a new study published in Ecology and Evolution.

The researchers found that when beehives are closer to managed grazing lands and commercial timber forests, they show a marked decrease in the number of microbes that are typically present in a healthy beehive. On the other hand, bees that pollinated swathes of natural land, like unmanaged wild grassland areas, showed higher microbial diversity in their hives.

Bees and other pollinators pick up microbes–such as bacteria–via the plants they pollinate. The greater the diversity of the flowers they visit, the more varied the palette of microbes they transport back to the hive. On lands where there’s less floral diversity–like man-made forests and farms–the bees therefore are less likely to encounter a broad spectrum of microbes. On wildlands harbouring greater biodiversity, the opposite is true.

But why do these microbes matter to bees? Biologists have discovered that one of the most important roles they play is in the cultivation of bee bread, pellets of compacted pollen that bees ferment and store in the hive, and from which they derive a large and crucial chunk of their nutrition. Microbes in the pollen are known to not only boost the nutrient-richness of this bread, but also arm the consuming bees with resistance to pathogens that occasionally infect the hive. 

While it was previously assumed that monoculture’s main threat was reducing the quantity of food available for bees, this study shows that the effects are more nuanced, potentially altering the health of individual bees and the resilience of the hive as a whole. “Since bee bread affects the ability of bee gut microbiome to resist infection by opportunistic pathogens, we therefore believe [there] could be an indirect link between landscape composition and bee fitness,” the researchers write.

They reached their conclusions by collecting bee bread samples from 29 hives spread across 23 sites in the Northwest of England. By extracting DNA from almost 500 individual bee bread samples, they could identify the diversity of microbes present in each sample. Combined with data on land use surrounding the hives, the researchers could infer the effect of the landscape on the microbial richness of each hive.

They also discovered that hives close to urban areas showed relatively low microbial diversity–despite the widespread assumption that suburban gardens are supportive habitats for bees. This may come down to the type of plants gardeners choose to cultivate: gardens filled with exotic species may be akin to a food desert for bees that have evolved to pollinate mainly native flora. So, pollinator-loving gardeners may be wise to fill their plots with bee-friendly flowers, the study hints.

Perhaps, like gardeners, farmers could also be compelled to make their land more accommodating to pollinators–as a kind of health insurance for the bees who work so hard to maintain our own sources of food.

Donkersley et. al “Bacterial communities associated with honeybee food stores are correlated with land use.” Ecology and Evolution. 2018
Image: Pexels

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