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Fri March 1, 2013
The Salt

Wild Bees Are Good For Crops, But Crops Are Bad For Bees

Originally published on Tue March 5, 2013 12:13 pm

Some of the most healthful foods you can think of — blueberries, cranberries, apples, almonds and squash — would never get to your plate without the help of insects. No insects, no pollination. No pollination, no fruit.

Farmers who grow these crops often rely on honeybees to do the job. But scientists are now reporting that honeybees, while convenient, are not necessarily the best pollinators.

A huge collaboration of bee researchers, from more than a dozen countries, looked at how pollination happens in dozens of different crops, including strawberries, coffee, buckwheat, cherries and watermelons. As they report in the journal Science, even when beekeepers installed plenty of hives in a field, yields usually got a boost when wild, native insects, such as bumblebees or carpenter bees, also showed up.

"The surprising message in all of this is that honeybees cannot carry the load. Honeybees need help from their cousins and relatives, the other wild bees," says Marla Spivak, a professor of entomology at the University of Minnesota. "So let's do something to promote it, so that we can keep honeybees healthy and our wild bee populations healthy."

Unfortunately, a second study, also released in Science this week, makes it clear that wild bees aren't having an easy time of it.

That study essentially follows in the century-old footsteps of Charles Robertson, "one of America's great scientists that nobody knows about," says Laura Burkle, an ecologist at Montana State University.

Robertson taught biology and Greek at Blackburn College in Carlinville, Ill., and he was fascinated by the close connection between insects and flowers. He spent years in the forests around Carlinville, carefully noting which insects visited which wild flowers at what time of year.

Burkle and Tiffany Knight, a colleague at Washington University in St. Louis, went back to Carlinville to see how much of the ecosystem that Robertson observed still exists today.

Much of the forested area around the town has been converted into fields of corn and soybeans — or suburbs. In the fragments of forest that remain, Burkle and Knight found all of the flowering plants that Robertson recorded in his notes a century ago. Of the 109 species of bees that Robertson saw, though, just over half seemed to have disappeared from that area.

"We don't know why," says Burkle.

One possibility might be a loss of nesting sites for these bees. But a changing climate may also play a role.

The bees that disappeared tended to be species that depended on just a few kinds of flowers for food. For those bees to survive, their preferred flowers have to be blooming when the bees start flying and need food. The warming trend might have thrown off that timing.

In fact, Burkle says, if you map the interactions between flowers and bees, they seem more tenuous now. Some flowers may get visited by just one or two kinds of bees, and maybe just for one week.

"I don't know that these systems can take a lot more environmental change without something drastic happening," she says.

Many bee researchers are trying to figure out how to help those native bees — and how to help farmers who benefit from them.

Claire Kremen, a conservation biologist at the University of California, Berkeley, who's a co-author of the first study in Science, says one of the biggest problems for wild bees is the agricultural specialization that has produced huge fields of just one crop.

The almond groves of California, for example, are a sea of blossoms in February. It's a feast, as far as the eye can see, for honeybees that come here from all over the country.

"But for the rest of the year, there's nothing blooming," she says.

That means there are no bees. "In fact, in places where we have very large monocultures of almond, we don't find any native bees anymore," Kremen says.

Planting other flowers in and around these almond groves, maybe as hedgerows, blooming all summer long, would help, she says.

Even better would be farms with smaller fields, and lots of different crops flowering at different times. Wild bees, Kremen says, need diversity.

Copyright 2013 NPR. To see more, visit http://www.npr.org/.

Transcript

STEVE INSKEEP, HOST:

If only Congress could be as efficient as bees. Some of the healthiest foods you can think of - blueberries, squash, almonds - would never get to your plate without the help of insects. No insects, no pollination. No pollination, no fruit. Farmers who grow these crops often bring in honeybees to do the job. And farmers get bigger harvests if there are wild bees around, like bumblebees. Yet those wild bees are getting harder to find. NPR's Dan Charles reports.

DAN CHARLES, BYLINE: A century ago, a man named Charles Robertson, a teacher of biology and Greek at Blackburn College in Carlinville, Illinois, was fascinated by the close connection between insects and flowers.

LAURA BURKLE: He's described as sort of one of America's great scientists that nobody knows about.

CHARLES: That's Laura Burkle, an ecologist at Montana State University. She says Charles Robertson spent years in the forests around Carlinville carefully taking notes on which insects visited which wildflowers at what time of year. Robertson's notes eventually were published. A few years ago, when Burkle was at Washington University in St. Louis, she and a colleague were reading about them and they wondered, where is Carlinville anyway?

BURKLE: You know, typed it into Google Maps and all of a sudden we realized that it's an hour and a half away from St. Louis.

CHARLES: So they jumped into a car and went for a visit. Much of the forest around Carlinville has disappeared. It's turned into corn or soybean fields or suburbs, but small wooded patches remain and Burkle and her colleague realized they could follow in Robertson's tracks. They could see if the same insects still are pollinating the same flowers.

They decided just to concentrate on wild bees, not other insects. They released their results this week in the journal Science. All of the wildflowers that Robertson saw still are there. But of the 109 species of bees that Robertson observed, half of them cannot be found anymore.

BURKLE: We don't know why they've gone extinct or at least locally extinct.

CHARLES: One possibility might be there's so little forest left there aren't enough places for wild bees like bumblebees or carpenter bees to nest. But it might also be related to a change in climate, Burkle says. The bees that disappeared tended to be species that depended on just a few kinds of flowers for food. For those bees to survive, the right flowers have to blooming when those particular bees start flying and need food.

Maybe the warming trend has thrown off that timing. In fact, Burkle says, if you map the interactions between flowers and bees, they seem more tenuous now. Flowers in a particular place may get visited by just one or two kinds of bees and maybe just for one week.

BURKLE: And so I don't know that these systems can take a lot more environmental change without something drastic happening.

CHARLES: Burkle's report was released this week side by side with another study which says wild bees aren't just good for flowers in forests, they also help put food on our plates. Dozens of scientists from 14 different countries looked at all kinds of crops that require pollination by insects, like almonds, blueberries, coffee, pumpkins, onions and strawberries. Farmers who grow these crops often pay beekeepers to bring in honeybees.

But the scientists found, even when there were plenty of honeybees, most crops produced a bigger harvest more reliably when native wild insects were visiting as well. Marla Spivak, a specialist on bees at the University of Minnesota, says this is really important.

MARLA SPIVAK: The surprising message in all of this is that honeybees cannot carry the load. Honeybees need some help from their cousins and relatives, the other wild bees. And let's do something so that we can promote it, so that we can keep our honeybees healthy and our wild bee populations healthy.

CHARLES: Some of the scientists who wrote this paper are also trying to figure out how farmers can attract more of these wild bees. Claire Kremen at the University of California, Berkeley says one big problem is specialization, huge farms of just one crop. The almond groves of California, she says, are a sea of blossoms in February, a feast as far as the eye can see for honeybees that come here from all over the country.

CLAIRE KREMEN: But for the rest of the year, there's really nothing blooming on that farm field.

CHARLES: So no bees.

KREMEN: Yeah, no bees. And in fact, in places where we do have very large monocultures of almond, we don't find any native bees anymore.

CHARLES: Having other flowers in and around these orchards, maybe as hedgerows, blooming all summer long, would help, she says. Even better would be farms with smaller fields and lots of different crops. Wild bees, she says, need diversity. Dan Charles, NPR News, Washington. Transcript provided by NPR, Copyright NPR.