Biologist Patty Jones Seeks Link Between Floral Chemistry and Bee Behavior

Though plants might seem vulnerable to the appetites of insects and other animals, they have a few weapons at their disposal: nasty compounds in their leaves that deter insects from eating them. One example are the cardenolides in milkweed.

Oddly, however, these toxic compounds are also found in flower nectar, the sweet reward that entices the kinds of insects and birds that can help flowering plants get pollinated. Patty Jones, assistant professor of biology, is trying to figure out this contradiction: how can nectar appear to both attract and repel? 

Though the plant-pollinator relationship is critical to global ecosystems and food systems, surprisingly little is understood about the chemistry of nectar. Nectar is a complex substance made up of several ingredients, including sucrose, fructose, amino acids, and yeasts. Because it is essentially like "a little sugar pot in the field," Jones said it often ferments, adding another ingredient to the mix—ethanol, or alcohol. 

While nectar is vital to plants, it may also play an important role in keeping bees healthy. And as bee populations decline, there is greater urgency to understand which flowering plant species are most beneficial for bees. "Nectar chemistry is a part of that picture," Jones said.

Jones's Three Hypotheses About Nectar and Toxicity

1. Costly Fermentation and Bad Bee Behavior: At the moment, Jones is looking at several possible expanations as to why nectar contains these toxic compounds. One of her hypotheses is that these substances in low doses don't hurt bees—and they prevent nectar from fermenting.

"If this is the case," Jones said, "then fermentation must have a cost." Plants might want to avoid the deterioration of their nectar, because one of the deleterious effects of fermentation could be altered bee behavior.

"Maybe alcohol doesn't deter bees from drinking a flower's nectar but changes their behavior," Jones said. "This could be the psychological or pharmacological effect of alcohol on their brains, or they could be reacting to how it tastes."

Fermentation could be bad news for a plant if it makes bees less consistent about visiting the same species or decreases the time bees spend on flowers. Bees in the wild become specialized on one flower type, returning again and again to that flower. Plants benefit from this loyalty, as it ensures their pollen doesn't get delivered to the wrong species. 

To understand the effect of alcohol on bee behavior and the problems it could create, Jones has been training colonies of bumblebees in her Druckenmiller lab. With the help of student researchers, she's been feeding her colonies a homemade nectar brew (made with store-bought sugar and distilled water). Half of the colonies receive a non-alcoholic mix; the others sip a mix with a low percentage of ethanol. Jones has created an experimental setup that allows her to safely release many bees at once to feed on her nectar, as well as release just one bee at a time.

Her first step is to "train" all her colonies of bumblebees to forage on just one type of flower—in her lab, either yellow or blue flowers (which are actually small plastic dishes—bees are easily fooled). She then observes a solitary bee in a novel setup that has an array of blue and yellow flowers that hold either all alcoholic or all non-alcoholic nectar. (The bees receive the same kind of nectar they had been receiving prior to the experiment.) She wants to see how "sticky" the bee is to the flower it had grown accustomed to, and whether alcohol has an effect on this.

In other experimental setups, the flowers have a bee decoy attached to them, because Jones also wants to know if alcohol affects bees' social behavior, such as changing how many bees visit a flower at any one time.

2. Good Bee Behavior: Jones's second hypothesis is that fermentation is not—in the end—costly, and that the toxic compounds or the alcohol change bee behavior in a way that actually benefits the plant, much like caffeine does in citrus flowers and coffee flowers. "Caffeine, when consumed by bees that are visiting those flowers, makes those bees remember the smell of that flower better," Jones said in the Nature Moments video, The Buzz About Bees, below. "So the presence of caffeine in the flower nectar probably increases the pollination rate of the plant and therefore benefits the plant."

3. Medicinal Nectar: A third hypothesis Jones is considering is that the compounds are not toxic to the bees but are rather medicinal, helping them recover from a detrimental gut parasite that is one of the factors driving bee declines. 

"Maybe the bees are using the chemistry from the plants to self-medicate against their own parasites, and therefore plants that provide that chemistry will be preferred, and thus pollinated more by bees," Jones said.