Surprise: Bees Need Meat

Surprise: Bees Need Meat

Microbes in flowers are crucial to bee diets, and microbiome changes could be starving the insects

Ask an entomologist what makes a bee a bee, and you’ll likely get some version of “bees are just wasps that went vegetarian.” New research shows that isn’t true. Bees are actually omnivores, and their meat is microbes. This finding may open a new window on why bees are in trouble: Anything that disrupts the microbial community in a bee’s food, whether it is high heat linked to climate change, fungicides or another stressor, could be causing developing bees to starve.

Bees are supreme pollinators because of what their babies eat. Most animals visit flowers to pilfer nectar, and they may or may not brush up against pollen and carry it to the next flower. Female bees, conversely, deliberately collect pollen, along with nectar, to feed their babes. This larval food choice is part of what defines a bee.

Scientists have known for decades that fermenting microbes are present in pollen, but no one had seemed to consider whether they were also an important food for bees. The microbes function as an “external rumen” that breaks down parts of the pollen. It stands to reason that bees might ingest some microbes, but two researchers decided to investigate whether they eat enough to make them omnivores—and if the bees truly need those microbes to thrive.

Prarthana Dharampal of the University of Wisconsin–Madison and Shawn Steffan, who works jointly at the university and the U. S. Department of Agriculture’s Agricultural Research Service (ARS), assessed 14 different bee species in six of the seven bee families. They found that bees eat substantial amounts of microbes, enough to change how they fit within food webs. Scientists use a scale to categorize where organisms belong in that web: those that make their own food, such as plants, register at so-called trophic position 1 (TP 1), herbivores register at TP 2 and carnivores do so at TP 3, or even higher if they eat other carnivores. The average TP across all the bees studied was 2.6, putting them squarely in the omnivore spot, halfway between herbivores and carnivores. Interestingly, the trophic position varied among families, ranging from just a bit above herbivores (2.11) to solid carnivores (3.09). Now that the TP is known, Dharampal says she wonders whether bees are really foraging for the pollen, or are foraging for the microbes that are associated with the pollen.

Courtesy PAIGE EMBRY Scientific American