Sonication or buzz pollination is the bumblebee‘s secret weapon of resonant vibration. When bumblebees (and a few other bee species) grab onto a flower and vibrate it by flying in place, securely attached pollen is dislodged. From BayNature.org:
Buzz pollination can be useful for releasing or collecting pollen from many types of flowers, but it is essential for some, including tomatoes, blueberries, and our native manzanitas. The anthers (male reproductive organs) of these flowers have only small pores through which pollen is released, like the holes in a pepper shaker. Sometimes wind or visits from insects can inadvertently shake out some pollen, but the amounts are small. Also, many of these flowers do not produce nectar, so honeybees ignore them anyway.
Bumblebees, by contrast, actively collect and eat not just nectar but also protein-rich pollen. And a bumblebee can cause a flower to discharge a visible cloud of pollen through buzz pollination. The bumblebee grasps the flower with its legs or mouthparts and vibrates its flight muscles very rapidly without moving its wings. This vibration shakes electrostatically charged pollen out of the anthers, and the pollen is attracted to the bumblebee’s oppositely charged body hairs. The bumblebee later grooms the pollen from its body into pollen-carrying structures on its back legs for transport to its nest.
See in action above in this video from the Smithsonian Channel: Slow-Mo Footage of a Bumble Bee Dislodging Pollen.
We also recommend Bees: A Honeyed History, a beautifully illustrated book about the bee life cycle, bee anatomy, swarms, the Waggle Dance, beehives, pollination, flowers and our food, bees and dinosaurs, and more.