Melissa Majoria

Melissa Majoria was the homeworld of Migrant Bees, some of which made their way to Earth. By 2009, the bees sensed that a catastrophe was about to befall the Earth, and began to make their way back to Melissa Majoria. (TV: The Stolen Earth) Donna Noble noticed this, and remarked it to the Tenth Doctor several times. He also found it odd. (TV: Partners in Crime, Planet of the Ood)

The catastrophe was Davros moving the Earth to the Medusa Cascade. The bees' movement created a disturbance on the Tandocca Scale, which allowed the Doctor and Donna to trace their path towards the Earth. (TV: The Stolen Earth)

Behind the scenes
The phenomenon of bees disappearing is a which has garnered some fair media attention.