London, July 3 : Scientists have said that a decline in bee biodiversity might spell trouble for crop producers as their differences are crucial to the maintenance of the world's crops.
According to a report in New Scientist, about a third of global food production, and possibly two-thirds of major crops, depends on pollination by animals, mainly bees.
Though vanishing bees have raised concerns for crops, researchers have now said that some crops may suffer even if there are plenty of bees around.
"The key is the different types of bees, not their overall number," said Pat Hoehn of the University of Gottingen, Germany. "This is bad news, as bee biodiversity is declining," he added.
Hoehn and colleagues took advantage of a natural experiment on the Indonesian island of Sulawesi, where farmers plant pumpkin patches in fields with varying amounts of shade, and the pumpkin vines climb to different heights above ground.
The team found that 25 different species of bee pollinated the pumpkins, with different sets of species visiting different pumpkin patches depending on the local temperature, humidity and height.
Because pumpkins have male and female flowers, they must be cross-pollinated to develop seeds. If insufficient pollen reaches the female flower it will develop fewer seeds, and smaller pumpkins.
The team watched which bees visited different pumpkin patches, and found that the more species of bees visited pumpkin flowers, the more seeds the pumpkins had.
The researchers then classified the bees into eight "guilds" - groups of species that all pollinated at the same time of day and height off the ground.
Bee species in the same guild also had similar body sizes. This determined how they behaved in the flower - whether they were small enough to walk around inside and redistribute pollen that had already been left there, or big enough to carry large amounts in.
Pumpkin patches growing in different conditions were visited by different numbers of guilds.
The plants visited by only three guilds averaged fewer than 200 seeds per pumpkin. Those serviced by six or seven had 400 or more seeds - as many as when the researchers themselves smeared ample pollen on the female flowers.
The data showed it was not the number of bees, or the number of species, but the number of guilds that made the most seeds.
This means, the team concluded, that the plants need different kinds of bees visiting at different times and behaving in different ways to get maximum pollination.
According to Jacobus Biesmeijer of the University of Leeds in the UK, "Diversity provides insurance against pollination failure."