Sonication or buzz pollination is a technique used by some bees to release pollen which is more or less firmly held by the anthers, which makes pollination more efficient. The anther of buzz-pollinated species of plants is typically tubular, with an opening at only one end, and the pollen is inside - smooth-grained and firmly attached. With self fertile plants such as tomatoes, wind may be sufficient to shake loose the pollen through pores in the anther and accomplish pollination. Visits by bees may also shake loose some pollen. However, the most efficient pollination is accomplished by a few species who specialize in sonication or buzz pollination.
In order to release the pollen, bumblebees and some species of solitary bees are able to grab onto the flower and move their flight muscles rapidly, causing the flower and anthers to vibrate, dislodging pollen. This resonant vibration is called buzz pollination. The honeybee rarely performs buzz pollination. About 8% of the flowers of the world are primarily pollinated using buzz pollination. The following plants are pollinated more efficiently by buzz pollination:
Greenhouse grown tomatoes are unproductive without aid in pollination. Traditionally pollination has been done by shaking using electric vibrators (one brand name was "Electric Bee"), however, it has been found to be less expensive in human labor and plant breakage to use bumblebees within the greenhouses. In Australia, as bumblebees are not native, and Australia has a number of widely publicised environmental disasters caused by escaped introduced species ("feral species"), research there is under way to adapt the use of the Australian native, Blue Banded Bees, for the same task.[1] This research is however competing with lobbying by potential importers of Bumble Bees, who would rather use those, disregarding the risk and the potential there for developing a "home grown" solution.
Photos and more complete explanation at the Tucson USDA bee lab: Why is that bee giving me the "raspberry?" [1]