Biology and Bees

By Lee Drutman

It has been estimated that bees pollinate 80 percent of our food crops and 80 percent of all pollinated plants. “Bees are important pollinators,” explains Robert Dudley, a professor of integrative biology at the University of California, Berkeley.

However, since most species of bees live in the tropics and most research is done in more temperate climates, there are a lot of unknowns about how bees operate.

Enter Brendan Borrell, a graduate student in the department of integrative biology and a self-styled man of the tropical bees. Borrell has been asking interesting questions about bees and coming up with interesting answers for years now. Recently, his article, “Thermal stability and muscle efficiency in hovering orchid bees,” coauthored with fellow graduate student Matt Medeiros, was published in the August 2004 issue of the Journal of Experimental Biology. Additionally, his article, “Suction feeding in orchid bees,” was published in the Royal Society Biology Letters and the relevant research was featured in Science Magazine online.

Borrell's first project was attempting to understand how orchid bees regulatetheir body temperature during flight. “It was actually a controversial topic,” Borrell explains.

That's because the conventional wisdom among scientists was that the flight muscles of the bee, which account for one-third of the insect's body mass, were used merely to lift the bee off the ground. Since the metabolic rate of the bee while in flight was so high-100 times that of a bee at rest-the bee would be unable to regulate body heat while in flight.

In order to determine whether this was an accurate assessment, Borrell did a combination of things. First, he filmed bees flying so he could examine closely the motion of their wings. Then he recorded how much carbon dioxide the bees were producing, their body temperatures after flight, and how much heat they were producing. Using an energetic model, he was able to determine how much heat energy was going into flight at cold temperatures as compared to warm temperatures.What he found was that at cold temperatures, the bees were beating their wings faster and producing a lot more heat.

“It's neat that they are able to regulate how much heat they produce,” Borrell says.“People didn't think this happened for flying insects….This helps to change the view of how sophisticated insect flight muscles are.”

But Borrell admits,“There's still controversy. It's a new approach and it's a difficult question to approach. Anything trying to measure a hovering insect is bound to be complicated.”

More recently, Borrell has turned his focus to the proboscis tongue of the orchid bee, which, when fully extended, is four times the length of its body. How and why did this superlong tongue-which operates as a soda straw-like tube-evolve and what impact does it have on how these bees gather nectar? That's what Borrell set out to answer.

“I wanted to look at the mechanics of how they drink nectar, and how this influences their behavior of foraging and how they pick which flowers,” Borrell said.

So, he caught 71 of the male orchid bees, since only males visit orchids, and let them roam around in an enclosure where he had created fake flowers out of cardboard and styrofoam, with artificial fragrance and sugar syrups of various concentrations ranging from 5 percent to 75 percent. Borrell found that the bees were most happy with the 35 percent solutions, whereas honeybees, who have a more cat-like tongue, prefer the 55 percent solution. As Borrell wrote in his paper in the Royal Society Biology Letters,“Energy flux during nectar feeding is maximized at an intermediate sugar concentration, the value of which depends on the morphology of the feeding apparatus and the modality of fluid feeding.” In other words, the type of tongue that bees have corresponds with the type of nectar that they prefer.

And how did such an odd tongue evolve in orchid bees, while most other bees have a smaller tongue in proportion to the rest of their bodies? “One probable evolutionary scenario is that as proboscis length evolved in concert with floral morphologies, anatomical constraints on glossal reciprocation would have rendered nectar transport via lapping less effective than suction feeding,” wrote Borrell. In other words, there was some co-evolution going on, with plants adjusting their shape so that longer tongues would be more effective at getting the desired nectar, and vice versa.

Still, Borrell is mulling over the data, which is going to be the basis of his dissertation.“What I found isn't totally clear yet,” he says. “Mechanics influenced decisions for sure, but I haven't decided how important these variables are when weighed with other ecological factors that influence decisions in the wild.”

As for what's next in Borrell's research, he says, “I'm getting more interested in behavior questions. Cognition is interesting in general because there are more complicated behavior tasks like looking at color and shape perception and other more complicated choice behaviors…. I'm interested in understanding how bees make decisions.”

With 300 species of orchid bees and most of them not well understood, Borrell will likely have plenty more fruitful research to conduct in the years to come.

“Most of the tropical insects are not real well known,” says Professor Dudley. “It takes a bit of effort to work there. It's a lot easier to stay at home and study lab rats or fruit flies.”