Why are bumblebees hired to pollinate greenhouse tomatoes? Why do some bees buzz when perched on a flower?

In some plant species, bees must vibrate the flowers to shake pollen loose. The technique is called buzz pollination or sonication.

Buzz-pollinated plants have anthers with very small openings so the pollen stays inside unless the anther is shaken. To collect the pollen bees grab the flower and vibrate their flight muscles. This makes a buzzing sound.

In the photo above, a halictid bee is releasing yellow grains of pollen as she shakes. She collects it on her legs for delivery to the hive.

Most species in the Solanum genus, including potatoes, eggplants and tomatoes, have to vibrate to release their pollen. Strong wind can do the trick outdoors but greenhouse tomatoes are out of luck. That’s how bumblebees get an indoor job.

(photo from Wikimedia Commons; click on the caption to see the original)