Bees are Healthy Eaters

Bees are Healthy Eaters
May 25, 2016

File this under “animals are smarter than humans.” New research from NC State University shows that honeybees will, for the most part, neglect soda and other foods with processed sugars in favor of sugar from flowers.

Postdoctoral researcher and lead author of the study, Clint Penick, says this research can help determine how urban bees live, and whether human behavior influences the diet of urban bees.

Honeybees spend their days flying around to collect sugar from their environment. Traditionally, they will gather their sugars from nectar found in flowers. They eat some sugars and save the rest for the honey-making process.

Penick wanted to figure out whether bees living in the city would still seek out flowers for their sugar, or whether they would instead get them from garbage and other human sources with processed sugars.

Honey BeeTo test this, Penick looked at bees from 39 colonies within 30 miles of Raleigh. Fifteen of those were wild colonies and the rest were managed by beekeepers, searching for processed sugars in the hives.

But then the question becomes how to tell processed sugars from natural ones, especially when the bees eat them and turn them into other things. The answer comes from a wrinkle in photosynthesis and how not all carbon atoms are created equal.  

Photosynthesis is the process by which plants harness energy from the sun to convert carbon dioxide into sugars, which are just small groupings of carbon, hydrogen and oxygen.

There is a point in photosynthesis in which an enzyme in the plant cell gathers carbon dioxide molecules and binds them together. In many plants, the first step is to build a molecule with 3-carbon atoms. This process, however, can go wrong if an oxygen molecule sneaks into the process. It leaves an unusable 2-carbon molecule with an oxygen atom sticking off of one end, which is a huge waste of resources for the plants.

Plants have to do all of the energy gathering for photosynthesis right at the surface of their leaves, because those cells get the most sun, and most plants will do the sugar-building—also called carbon fixation—at the surface as well. These plants are called C3 plants because their first step is to build that 3-carbon molecule.

The trouble is, the process of gathering energy from the sun generates oxygen, so while C3 plants are trying to build their 3-carbon molecule at the leaf surface, they keep running into the oxygen molecules made from the sun’s energy, and the C3 plants end up wasting a lot of energy making unusable 2-carbon products. 

Some plants, however, have evolved a fix. Their first step is to create an organic acid made with four carbon atoms, which is why they are called C4 plants. The C4 plants then move that organic acid to cells on a leaf’s veins where there is not as much oxygen around, break the acid down into carbon dioxide and finally build the 3-carbon molecules away from the oxygen.

That might seem like a lot of work, but C4 plants reap huge benefits and are able to grow far more quickly than C3 plants. It is not a coincidence that many large-scale food crops like sugar cane and corn come from C4 plants. And since much of the processed sugar in the human diet comes from either sugar cane or corn syrup, anyone eating sweets or drinking soda is getting a healthy dose of C4 plant.

There are a few different isotopes—a chemistry term denoting that different atoms of the same element can have different masses—of carbon. The most common isotope is carbon-12, which gets its name from the six protons and six neutrons in its nucleus. C4 plants, for some reason, have an uncanny ability to pick up lots of carbon-13, which is no different from carbon-12 in any way except that it has seven neutrons instead of 6.

HoneyCarbon-13 makes up about one percent of all the carbon on Earth, and the level of carbon-13 in C3 plants roughly mimics that because they take whatever carbon they can find. C4 plants, however, and everything they make contain a higher percentage of carbon-13. So when bees or anything else eat lots of C4 products, including processed sugars, they wind up with a high percentage of carbon-13.

Penick tests the carbon-13 levels in bees from all the hives and found that wild rural bees predictably showed normal levels of carbon-13, as their only option for food is C3 wild flowers. 

The surprise was that wild urban bees eschewed the easy to find and energy dense soda and food scraps available in any garbage can for more natural sugars. The carbon-13 levels in urban bees were similar to those in the rural bees.

The biggest spike in processed sugars came in domesticated bees. Many beekeepers will supplement their hives’ diets with sugar water, which shows up as a big carbon-13 spike in the domesticated bees.

There are a few reasons why this is important. First, as honeybee populations are in decline, scientists and beekeepers are looking for ways to preserve them and keep them healthy. Learning that urban bees aren’t primarily living on a diet of old soda perhaps alleviates one worry that a human-provided diet could be harmful.

Second, honey gets its color and flavor from the combination of flowers the bees visit. According to the National Honey Board, there are more than 300 types of honey in the United States ranging from clover to orange blossom to avocado.  Urban beekeepers now don’t have to worry about adding “dumpster” to the list of honey flavors, and that’s something we can all be thankful for. 

—Daniel Lane

Daniel Lane covers science, medicine, engineering and the environment in North Carolina.