Bees have a much greater economic value than is widely known, according to a scientific probe into strawberry-growing published on Wednesday.

Strawberries pollinated by bees were of far higher commercial value than fruit that was self-pollinated or pollinated by the wind.

They were heavier, firmer and redder and had a longer shelf life, researchers in Germany found.

Bees are under threat from hive ‘collapse’, a disorder that some have linked to pesticides and pollution.

According to a 2011 report by the UN Environment Programme (UNEP), pollination by bees and other insects contributed about 153 billion euros ($204 billion), or 9.5 percent, of the total global value of food production.

But such estimates could be far short of the mark, the new study said.

A team led by Bjoern Klatt at the Department of Crop Sciences at the University of Goettingen in Germany planted nine commercial strawberry varieties in an experimental field.

The plants were either covered with special gauze bags to allow pollination by the wind or other parts of the plant, or were left open for visiting by bees.

The fruits were collected and graded according to standard commercial criteria for attractiveness.

They were then put through a battery of lab tests for objective assessment of colour, firmness […]