They are small creatures with tiny brains, but honeybees are the most important pollinators on the planet, pollinating one third of everything we eat.

Yet bees are dying off around the world and nobody knows why.

China's indigenous honeybee (Apis cerana) previously survived under varied geographical conditions.

Recently, however, their population has decreased due to environmental pollution and competition from Italian bees (Apis mellifera ligustica) that were introduced to China just before the turn of the 20th century.

With the demise of bees, pollination relies increasingly on the wind and human intervention.

Pears are a specialty of Hanyuan county, Sichuan province. Farmers here can usually harvest about 5 tons of pears a year, but this depends on artificial pollination rather than honeybees.

Each April, the farmers collect flowers, brush and male anthers to obtain pollen, which will be dried for two days.

Farmers tie a handful of feathers on a long bamboo pole, to imitate the hairy bodies of bees, and the feathers are lightly dipped in pollen and then applied to flowers so they are pollinated.

Each spring, hundreds of farmers climb up trees to pollinate flowers, one by one.

"It was unbelievable the first time I saw farmers doing it," says Tang Ya, a pollination researcher from Sichuan University.

"For fruit growers, artificial pollination can guarantee profits, but as more young people leave their homes to seek jobs in cities, I'm afraid that artificial pollination will be very difficult to achieve in less than two decades".

A hive of bees can pollinate 3 million flowers a day, but a person can pollinate only 30 trees.

"We rely on bees to pollinate and they are in trouble for various reasons, so unless we want to eat just corn, wheat and rice, we need bees," says farmer Cao Hongyuan.