Powerful Pollinators, Wild Bees May Favor Eco-Farms

Ben Harder
for National Geographic News

Updated October 28, 2004

Organic farming is not only friendlier to the soil and the environment
than conventional farming, it's also friendlier to an underappreciated
agricultural workforce—wild bees. So indicates research on how well
bees distribute pollen across different types of cropland.

The finding has economic implications for farmers, many of whom currently rely heavily on domesticated bees to perform crop pollination, Princeton University conservation biologist Claire Kremen told National Geographic News.

If farmers restored natural habitats near their lands and used more organic cultivating techniques, resulting growth of wild bee communities might reduce growers' dependence on European honeybees, the domesticated variety, and ultimately pay financial dividends, she said.

Kremen added that such farming methods would also offer insurance against the possibility of further declines among European honeybees, which have suffered setbacks in recent years. Pesticides, diseases, and other deadly agents have taken their toll over the past decade.

Furthermore, domesticated colonies that have crossbred with Africanized "killer" bees have been rendered too aggressive for beekeepers to manage, further depleting their availability to farmers, said bee researcher Robbin W. Thorp of the University of California–Davis.

"Pollination is an incredibly important ecological function," Kremen said. Bees function as pollinators because, as they feed on flower after flower, they unintentionally shuttle grains of pollen from one plant to the next. Without bees to do that lifting, many common North American plants—including numerous economically important crops—would go unfertilized and would be unable to reproduce, she said.

For more than a century, the most popular pollinators among North American farmers have been domesticated descendants of imported European honeybees, said Thorp. He estimated that 3,500 to 4,000 species of non-domesticated bees that are native to North America can also pollinate crops—when they can survive on or near croplands.

But modern intensive farming practices often don't provide all the resources bees need to stay alive. Beekeepers take care of domesticated bees, while the wild bees are left to subsist on shrinking wild habitats.

Homegrown Labor Movement

"We don't necessarily need to rely on honeybees," said Kremen. In fact, she said, farms with sufficient numbers and types of wild native bees theoretically don't require the domesticated honeybees at all. "But the caveat is that we only find sufficient numbers of native bees in areas that are near native habitat."

Kremen reached that conclusion after she, Thorp, and Neal Williams of Princeton Unversity conducted experiments on watermelon plots in California. The research trio considered two important factors about each plot: How much natural habitat existed near the farm, and whether the farm relied on organic or conventional cultivating techniques.

The researchers measured the abundance and diversity of wild bees on all three types of farms during the 2001 growing season. They also measured how rapidly pollen accumulated on flowers living on each farm type. Domesticated bees weren't used during the experiments.

Kremen and her teammates found more than twice as many bees—from more than twice as many different species—on organic farms near wild habitats than they did on either organic farms farther from natural habitats or conventional farms close to nature.

The researchers also found that native bees delivered an average of nearly 1,800 pollen grains per day to each flower on organic farms near natural lands, but only about 600 and 300 grains per flower per day, respectively, to the second and third farm types. About 1,000 pollen grains per flower per day are required for successful fertilization, they estimated.

"On organic farms near natural habitat, we found that native bee communities could provide full pollination services," the researchers concluded in a paper that will appear in an upcoming issue of the journal Proceeds of the National Academy of Sciences.

"All other farms, however, experienced greatly reduced diversity and abundance of native bees, resulting in insufficient pollination services from native bees alone," the trio wrote.

A Beeline for the Bottom Line

Kremen said that farming techniques that appear friendly to native bees include avoiding herbicide and pesticide use; growing a diversity of crops on each plot of land, rather than a single crop; and cultivating some plants that don't have economic value on their own but that help provide a continual supply of food for native bees. In some cases, she said, it may even be advantageous to allow weeds to grown along the borders of fields.

"We couldn't do away with honeybees all together," said Kremen. But, she said, farmers could "reduce the [number of] honeybees that they rent and plow that money into these small restoration efforts," which could help native bee populations grow and might ultimately pay dividends.

The resulting diversity of bee species would also offer an insurance policy against, for example, attacks by parasites that pray mainly on honeybees.

"If honeybees continue to decline, [these farmers] will be better off, because they'll have these natural pollinators," said Kremen.

"As we destroy natural habitats, we are reducing our options," she said. "We are destroying an insurance policy."