Coffee growers who want to boost their crop for free should hire an army of willing, unpaid volunteers: the bee.

The mainstay of the world coffee business, Coffea arabica, is a self-pollinating shrub that is not supposed to gain anything by being exposed to insect pollinators.

But US scientist David Roubik of the Smithsonian Tropical Research Institute has found that conventional wisdom has got it all wrong – the African honeybee, he found, can increase crop yields by half by helping the pollination effort.