Good Vibrations: Montana State researcher wins NSF grant to study buzz pollination

BOZEMAN - Scientists have long understoog that bees sometimes shake flowers to collect pollen in a process called buzz pollination. But how the pollen mobilizes within the flower is not clearly understood. Now, a mechanical engineer at Montana State University is using nearly $585,000 in recent funding from the National Science Foundation to learn precisely how some bees vibrate their way through their critical role in the pollination process.

In order for some plants to bear fruit or vegetables, the pollen from the male part of the plant - the anther - must be transferred to the female parts of the plant, called the stigma and pistil. Plants rely on pollinators such as birds, bees and other insects to jump-start this process.

This research is especially timely as the number of pollinators continues to decline globally.

"It's generally accepted that bumblebee populations are shrinking, and bumblebees are one of the big species that is performing buzz pollination," said Mark Jankauski, associate professor of mechanical and industrial engineering in MSU's Norm Asbjornson College of Engineering. "If those populations are declining, it's a bad thing in terms of food security."

And as pollinators such as bees continue to decline, he said, so does the amount of food the plants would otherwise produce. That's why farmers and scientists alike, in the interest of food security, would like to create efficient means of artificially pollinating plants.

"We're hoping that this research can, in the long term, facilitate the development of artificial pollination technology so that there's a robotic system, or something along those lines, that can come in and kind of supplement the natural pollinators," Jankauski said.

Pollen is easily accessible in most plants because their pollen-producing anthers typically split open to expose it. But pollen in a small percentage of flowering plants, including tomatoes, huckleberries and eggplants, remains sealed inside the anthers until it is forced loose. This is facilitated by certain bees, who grasp the anthers with their jaw-like mandibles and rapidly vibrate their flight muscles, shaking the pollen through tiny openings in the tip of the anther like salt from a saltshaker.

"Bees of different species will apply different frequencies to the anther; they'll shake it at 100 times per second or 200 times per second up to about 400 times per second," Jankauski said. "But why they choose a specific frequency isn't particularly well known. And so, we want to understand more about kind of the relationship between what the bee is doing, how hard is it forcing, how fast is it shaking it and what that actually does to the pollen inside."

To help answer these questions, Jankauski and mechanical and industrial engineering doctoral student Mitch Alvord, have built a shoebox-size contraption designed to vibrate pollen out of a tomato plant's anther. At one end of the box, two studio lights illuminate the anther from behind. At the opposite end, a specialized video camera captures the action in thousands of frames per second. The result is a high-resolution, slow-motion video of what happens when a pushrod vibrates a sealed anther, forcing it to release its pollen.

"This device is called an electrodynamic shaker," Alvord said. "You can think of it as a speaker, and then I can tune frequency and amplitude that I want to vibrate these anthers with.

"We're being the bee in these experiments, and we're vibrating the flowers at different frequencies," Jankauski added.

He said that over time, bees become more efficient at vibrating a blossom until the pollen pours out.

"It certainly is a learned behavior," he said. "They'll land on a flower, and they'll change their buzzing frequency a little bit. And they get more effective at this throughout their lives."

Erick L. Johnson and Sarah Morris, associate professors of mechanical and industrial engineering in the Norm Asbjornson College of Engineering, are co-principal investigators on this project.

"This research reflects the best of Montana State's land-grant mission: advancing fundamental knowledge while exploring solutions to real-world challenges," said Alison Harmon, MSU's vice president for research and economic development. "By uncovering how buzz pollination works, Dr. Jankauski's team is contributing insights that could ultimately benefit agriculture, food production and environmental sustainability."