from the Environment News Service:

http://ens-news.com/

Industrial Farming Causes Trouble for Bees

PRINCETON, New Jersey, December 20, 2002 (ENS) - Intensive, industrial
scale farming may be damaging one of the very natural resources that
successful crops require: pollinating bees.

A study by scientists at Princeton University found that native bee
populations plummet as agricultural intensity goes up. In farms studied
in and around the Sacramento Valley in California, concentrated farming
appeared to reduce bee populations by eliminating natural habitats and
poisoning them with pesticides, the researchers reported.

U.S. farmers may not have noticed this effect because they achieve much
of their harvests with the help of imported bees rented from beekeepers.
These rented bees, however, are in decline because of disease and heavy
pesticide use.

The study, to be published this week in an online edition of the
"Proceedings of the National Academy of Sciences," found that native
bees are capable of doing a lot more pollinating than previously
believed. But it would take careful land use to take advantage of that
capacity, the researchers concluded, because current high density,
pesticide dependent agriculture cannot support native bees.

"This is a valuable service that we may actually be destroying through
our own land management practices," said Princeton ecologist Claire
Kremen, who co-wrote the study with Neal Williams, a postdoctoral
researcher, and Robbin Thorp of the University of California-Davis.

Suppressing the many species of native bees and relying on just a few
species of imported ones may be risky, said Kremen. Farmers who use
managed bee populations - that is, most commercial farmers - depend on
fewer than 11 species out of the 20,000 to 30,000 bee species worldwide.


Other researchers have estimated that $5 billion to $14 billion worth of
U.S. crops are pollinated by a single species of bee, the European honey
bee.

"Right now we are really very dependent on that species," said Kremen.
"If something happened to that species and we haven't developed other
avenues, we could really be in great difficulty."

The researchers spent two years examining watermelon farms located at
varying distances from oak woodlands and chaparral habitats that are
native to the Sacramento Valley. They also looked at land that was
farmed with pesticides and without pesticides. They focused on
watermelon because it requires a lot of pollen and multiple bee visits
to produce marketable fruit.

They found that native bee visits dropped off in the farms that were
distant from natural habitats and that used pesticides.

"We could then multiply the number of visits by the number of [pollen]
grains deposited per visit and sum that up for all the species and
figure out how much pollen the watermelon plants were receiving," said
Kremen. "We found that, where it still flourished, the native bee
community could be sufficient to provide the pollination service for the
watermelon."

One interesting finding, said Kremen, was that the mix of native bees
providing the pollination was very different in the two years of the
study. In one year, a few strong pollinators accounted for most of it,
while in the other, many species contributed.

"That says something about the need for long term studies and also
argues for the need to maintain diversity," said Kremen.