[Pollinator] Bumble bee flower choice article

[Kimberly Winter]

Thanks to NAPPC Partner Larry Stritch for sending this insightful article 
about research on bumble bee flower selection (and some frightening 
implications for spreading invasive plants):

http://www.uwm.edu/News//Features/06.10/Bumblebees.html

Flight of the Bumblebee:
Researchers Find that Flower Choice Matters
By Laura L. Hunt

Bee photo by Jeffrey Karron

Rebecca Flanagan has probably come as close as a human can to reading the 
mind of a bumblebee.

Flanagan, a graduate student in biological sciences, and Associate Professor 
Jeffrey Karron are studying the behaviors of bees as they gather pollen – 
which plant species the bees forage on, which flowers they probe and in what 
order, and how many blooms they visit before moving on to another plant. In 
doing so, the bees make plant reproduction possible by dispersing pollen.

To predict where each bee that she tracks will carry its pollen next, 
Flanagan has to literally think like one.

“Once they’ve learned a foraging style that’s been successful, they are more 
likely to stick with it rather than invest time in learning something new,” 
says Flanagan.

But why go to such lengths to map the flight of the bumblebee? It may seem 
random and inconsequential. But it is neither, says Karron.
The bees are pivotal players in determining which plant populations survive 
through successful reproduction. If scientists could better understand 
nature’s decision-making process, then they could use the information to 
increase crop yields and to boost conservation of native plant communities.

Best bee practices


Associate Professor Jeffrey Karron (above), graduate student Rebecca 
Flanagan and undergraduate Dustin Knutowski (below) in their experimental 
garden at the UWM Field Station

photos by Pete Amland



Because there are many bee behaviors, the task isn’t simple, but with 
tedious scrutiny it is documentable.
“Bumblebees definitely have distinct foraging patterns, both among species 
and even individuals of a single species,” Karron says. In fact, some of the 
many different behaviors lead to far more fruitful propagation than others.

To understanding foraging patterns, the team must manipulate every variable 
they can feasibly control in a natural setting.

But the experimental garden they keep at the UWM Field Station in the 
Cedarburg Bog is far from the sterile laboratory, and the complexity of 
their experiments becomes immediately evident: There are more options here 
than clothes in a teenage girl’s closet.

Nonetheless, Karron and his research group have developed an unparalleled 
data set by testing the effects of various combinations of plant species on 
their reproductive patterns.

Twice funded by the National Science Foundation, Karron’s research centers 
on the reproductive biology of monkeyflower, a wetland plant native to 
Wisconsin. Karron’s lab uses several innovative methods of tracking monkey 
flower mating, and all hinge on where the pollen comes from.

Pollen allows the flowers, which contain both male and female reproductive 
organs, to produce seeds. Plants can only produce seeds from their own 
species’ pollen. The pollen from another species deposited on a 
monkeyflower, for example, is simply wasted.

The most effective reproduction occurs through cross-pollination – when 
pollen deposited on a flower is brought from a different plant of the same 
species, either from one pollen donor or many. When pollen is spread from 
one flower to another on the same plant – called self-pollination – seed 
production is considerably lower and the resulting seedlings are much less 
vigorous.

Using genetic analysis to establish paternity, Karron has demonstrated that 
adjacent flowers differ markedly in their mating patterns.

“It’s amazing what we’ve found,” he says. “When a bee visits the first 
flower on a plant, 80 percent of the seeds are cross-pollinated. But by the 
time the bees have landed on the fourth flower on that plant, 90 percent of 
the seeds are self-pollinated.”

Bee magnets
Flanagan has taken the research of Karron a step further by testing whether 
the inclusion of purple loosestrife, an invasive weed that chokes wetlands, 
will affect the seed production of monkeyflower.
She has set out the garden in a grid of numbered holes. In this way, she can 
rotate the kinds of potted plants that are dropped in each morning and the 
density of each species in the plot. On any given day, Flanagan will trim 
the plants so that each has the same number of flowers on it.

Then she tracks one bee at a time, calling out its exact foraging sequence 
by number to her undergraduate assistant, Dustin Knutowski, who charts the 
path.

In the time she has spent working at the garden, she says, the invader plant 
is the heavier “bee magnet.” And if that’s the case, purple loosestrife is 
luring pollinators away from the native plants.

To investigate her hunch further, Flanagan added a third wetland species to 
the garden – a native plant known as “great blue lobelia.” So far, the bees 
continue their strong attraction to purple loosestrife.

“This preference for purple loosestrife or other exotics could threaten 
reproduction of native plants and have devastating effects on ecosystems,” 
Karron says.

Who’s your daddy?
Calculating paternity could be a nightmare. Because pollen from multiple 
monkey flower plants can be deposited during a single bee visit, seeds 
produced by one flower can be “sired” by pollen from up to nine different 
plants.
So Karron uses genetic markers to unambiguously determine which plant 
fathered each of the thousands of seeds he samples. He is working backwards 
to get at the same question Flanagan seeks – where the bees have been.

He divides each of the plants in the garden to create an exact copy of each 
population.

Imagine having 20 sets of identical twins, he says, and dividing them into 
two groups that are exact copies of one another. That is what Karron has 
done with his garden, only he has produced many identical sets so that he 
can subject them to different ecological conditions.

Karron is proud of the fine level of detail his techniques have produced.

His research group was the first to demonstrate that mating patterns differ 
dramatically among individual flowers and the first to show that the 
presence of competing plant species influences mating patterns.

“Using multiple strategies,” he says, “we are able to answer questions that 
no one else has.”







~Kim

--> Bee Ready for National Pollinator Week:  June 24-30, 2007.  Contact us 
for more information at www.pollinator.org <--

Kimberly Winter, Ph.D.
International Coordinator
North American Pollinator Protection Campaign
Internet: www.nappc.org, www.pollinator.org
Ph: (301) 219-7030