Sonication or Buzz Pollination
Pollination and Vibration
As a child you learned about bees and how they fly from flower to flower pollinating the plants, and that they carry the pollen on the hairs of their legs while some even carry it on hairs their bottoms (called scopa). However, there's another way that bees can pollinate that most people don't know about and its immanently useful for gardeners to be familiar with. The process is called sonication or buzz pollination.
Flowers are tricky things. They've evolved along with their pollinators in a reward-based system where pollinators get beneficial snacks of protein (pollen) and sugar (nectar) for visiting the flowers and then carting off their pollen to other flowers. This keeps the ol' sunflower from having to move around to mate, and the pollinators get the perk of tasty and nutritious food. Here's where you're going to have to think back to your plant anatomy for a moment. The male parts of a flower are called the anthers. The anthers produce pollen which is carried by the pollinator to the pistol of the flower (composed of the stigma, style, and ovary of the flower). When the pollen lands on the stigma, which is usually sticky) it grows a pollen tube and fertilizes the flower so we can have our yummy tasty ovary fruits such as apples, oranges, peaches and pears.
Now in most cases the anthers of a flower simply open their pores and expose their pollen to the bee or insect that flies over and does the hokey-pokey on the flower to get the nectar and pollen. However, not all plants do this. Some plants have flowers with tubular anthers. The technical term for this is poricidal (pore-eh-side-al) anthers. Examples include (but are not limited to):
Other poricidal plants include those in the Fabacae family (some peas, legumes, and chestnuts) and Solanaceae family (nightshades: like eggplants, potatoes and tomatoes). About 8% of flower plants are thought to be poricidal (I love this term).
In plants with flowers like this, the tubular anthers are usually long, with short stamens (bits that the anther sits on), and they have a tiny opening at the top that a bee can't fit into. Added to this challenge, the tubes usually face up or are horizontal and the pollen won't just fall out. So what's the deal? How can a plant expect any pollinator to carry its pollen around if the pollen is stuffed in a long tube with a tiny opening? The amazing answer is an adaptation called sonication or pollination by vibration. To get at the tasty protein snacks inside the tube bee vibrate the pollen loose. The bees use their wing muscles to create high speed vibrations to knock the pollen loose from the tube. Some bees may sit in one place and vibrate while others may vibrate the entire flowers. Turn up the volume on your computer and listen closely to this bee as it uses sonication on the flower:
You'll notice that the bee vibrates its wing muscles, not its wings. The wings are completely closed. The force from this sonication can reach up to 30G's!!! This is near the limit of the forces that humans can stand.
Listen to this bee use sonication to pollinate a poppy flower:
So, why have poricidal anthers? The answer is that by having open pores on your anthers, as a flower, you get diminishing returns on visits by bees. If all your pollen spores just fall out and one bee comes by then it's likely that that one bee will take everything off with it if it can. However, if you can put your pollen in a tube, and disperse it at intervals, then there's a chance that you'll get more visits by more than one bee. You see, many of the flowers are made in such a way that they only release a little of their pollen at once, no matter how hard the bee buzzes or sonicates. This ensures that the flower will be visited again, and that there is a higher probability of the flower spreading its pollen and genetic material farther and to other flowers. Here's a fun paper by Harder and Barclay from the Functional Ecology Journal if you'd like to know more: https://www.jstor.org/stable/2390076?seq=1#page_scan_tab_contents.
There are many types of bees that sonicate, ranging from the big fat lazy bumblebees that you think of (Bombus) to carpenter bees and even sweat bees. Funny thing though, honey bees can't sonicate. This means that the tomatoes and eggplants in your garden have to rely on native bees, and those that can do buzz pollination. In many cases greenhouses and commercial farmers have to sonicate their own flowers. Check out this video of a tuning fork releasing pollen from a flower:
You can buy a sonicator on Amazon for your garden:
But it's cheaper and easier if you just use an old electric toothbrush. This works just as well and you can change the head when you're done. (or you could invent eggplant flavored toothpaste and make a fortune!)
Sonication and buzz pollination is really amazing. It's something that you would never know about if you didn't take the time to sit and watch the bees. I high recommend some good quality garden time, observing your plants and their pollinators. without them we wouldn't have the tasty vegetables that we eat every day! You can read more about sonication or buzz pollination on the website of the Leonard Lab, from the University of Reno in Nevada: http://www.anneleonard.com/who-we-are/.