While vanishing bees
have raised concerns for crops in the US, German researchers say some
crops may suffer even if there are plenty of bees around. What matters is the
different types, but bee biodiversity is also declining.
About a third of global food production, and possibly
two-thirds of major crops, depends on pollination by animals, mainly bees.
Pat Hoehn of the University of Göttingen, Germany
and his colleagues realized the key to future while watching pumpkin
cultivation on the Indonesian island
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, writes Debora
in New Scientist.
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.
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
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.
Biesmeijer of the University
of Leeds in the UK, points out
that plants have different pollination strategies. Some have specialised
flowers and only one or two pollinator species - the pollinators are efficient,
but the plant is in trouble if those species are harmed.
Others have wide open flowers that can be pollinated by many
species. For these, he says, "diversity provides insurance against
A group of pollinators is likely to be active during a
broader range of climatic conditions, so together they provide better
pollination service to certain crops." On the other hand, no one species
is very efficient, so the plant needs the diversity.
Human-induced habitat change is hurting many pollinators,
says Biesmeijer. "Crops with specialist pollinators will be hit hard if
their visitor is affected. The new study seems to show that even crops with
'back-up plans' - a number of pollinators - can be adversely affected by
In a world where food
production needs to increase, the team hopes these results will lead
to more efforts to conserve bee species.