Dr Adam Hart continues his exploration of migratory beekeeping in the United States. Each year the beekeepers of America travel to the annual Almond bloom in California, the largest single pollination event on Earth, a thousand square miles of almond orchards bloom in unison, turning much of California's Central Valley white. Seventy-five per cent of the world's almonds come from these orchards and to ensure successful pollination, farmers need bees - a lot of bees: 1.5 million hives, or over 30 billion bees, swarm over the bloom for three weeks a year. But beekeeping on this scale carries with it a host of threats from diseases, pests, agricultural insecticides and even starvation.

In this second part of the programme Adam explores the nature of some of those threats, including the mysterious condition known as colony collapse disorder or CCD. He also talks to UK researchers about the latest EU ban on a specific kind of pesticide which could be affecting the ability of bees and other pollinators to collect nectar and navigate.