According to the annual survey by international Apiary Inspectors, evidence shows that honeybees are in a rapid and probably terminal decline. For the fourth year in a row, more than a third of colonies did not survive the winter in the US. Bernard Vallat, the World Organisation for Animal Health's director-general, warned, "Bees contribute to global food security, and their extinction would represent a terrible biological disaster." The decline of the country's estimated 2.4 million beehives started in 2006. Since then more than three million colonies in the US and billions of honeybees worldwide have died and scientists are no nearer to knowing what's causing this.