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Bumblebees: A new role as pollinators?Bumblebees: A new role as pollinators?

David Bennett 1

February 2, 2012

7 Min Read
<p> CAN NATIVE POLLINATORS such as bumblebees help to fill the gap created by the decline of honeybee populations in many areas of the U.S.?</p>

With the hammeringthat honeybee populations have taken over the last few years, farmers have been reminded how vital pollinators are for good yields. And as honeybee hives continue to be hit with odd maladies, the question is: Can native pollinators fill the gap?

Research in northwest Arkansas is looking at how bumblebees can fit the bill. Can they be enticed to artificial nesting boxes? Can farmers count on different species’ life cycles to pollinate certain crops?

For the next several years, Amber Tripodi, a graduate student at the University of Arkansas, will be conducting studies to answer those, and other, questions. Among her comments:

On the reasons for researching bumblebees…

“I was drawn to insects as a tiny kid, just watching them. Entomology was just something I was naturally inclined toward. At the same time, I’m also very interested in sustainable agriculture and environmental conservation. Studying pollinators is a nice mix of my interests. We have a lot of interesting native bees that have special behaviors.

“Recently, with the honeybee declines, we began looking at what native pollinators might already be doing and how we might help them to pollinate our crops.” 

On work other than the study on bumblebee nesting…

“There has been a lot of talk recently about bumblebees declining throughout the United States. Through work with honeybees, researchers began noticing that bumblebee populations were also tanking in some areas.

“In Arkansas, a survey on bumblebee species was done in the 1960s. One, the ‘American bumblebee,’ was called the ‘most common, widespread and abundant species in the state.’ But now, after collecting and sampling throughout the state, that doesn’t seem to hold true any more.

“So, one of the things I’m looking at is whether we can use genetic diversity information on populations to see if we can determine if bumblebee populations are stable or are declining.

“With the genetic diversity aspect, I’ve gathered a lot of interesting data. It would be nice to have a state distribution of bumblebees, county-by-county, and a good baseline to judge how well the populations are doing.”

For more, visit the following sites: http://comp.uark.edu/~aszalan/Apis/Bumble_Bee_Research.html and http://comp.uark.edu/~aszalan/Apis/Native_Pollinator_Outreach.html.

On bumblebee nesting habitat work…

“I’m building the boxes this winter and will start the first trial in the spring. We’ll see if any bumblebees move into the boxes and, if so, which ones.

“That will be a two-year trial and at the end I hope to have recommendations for ways farmers can use bumblebee houses to augment populations on their farm.

“Bumblebees typically live underground. The normal, natural nesting habitat for most species is abandoned rodent nests. So, there’s a defensible entrance — a tunnel with a constricted opening to easily defend their nest and honey. They use hair and straw from the departed mice as insulating material to keep the brood warm.

“Nest sizes vary. With some species, there may be 50 or so bumblebees. Other nests can be much larger — 400 or more individuals.”

On differences between honeybees and bumblebees…

“Honeybee colonies will last for two or three years. During that time, a queen produces thousands and thousands of workers that are the pollinators.

“Bumblebees, on the other hand, have an annual cycle. A bumblebee queen starts a colony in the springtime after overwintering by herself underground. When she finds a place to nest, she’ll go out and forage and start with a small pile of wax, pollen and nectar. She’ll then lay eggs on a small wax ‘pot.’

“She keeps those eggs warm, and when they hatch she feeds them on her own. Once raised, that first batch of workers take over. The queen stays in the nest and the workers go out and get food for the colony.

“With honeybees, when it’s time to start a new colony, the queen takes a large number of workers with her. When they find a good place to live, the workers immediately go out to collect pollen and nectar.

“Honeybees are very advanced in their social behavior. Bumblebee social behavior is much more primitive.”

On other differences between the two…

“One of my favorite, interesting differences between honeybees and bumblebees is ‘buzz pollination.’ Bumblebees, carpenter bees and a handful of others — some of the leaf-cutters — do this.

“Some flowers — say tomato or blueberry — have anthers with pollen deep inside a tube instead of on the outside. To buzz pollinate, the bees will twitch their flight muscles and produce an audible buzzing sound. That frequency releases pollen from the tubes that covers the bee. This makes them very efficient pollinators of crops like tomatoes and blueberries.”

On bumblebee versus honeybee pollination efficiency…

“The reason we have favored honeybees traditionally is because we know how to raise them. We’ve been doing it for thousands of years, so we’ve become good at it.

“A honeybee colony may have 100,000 individuals. As an individual, one honeybee may not be as efficient at pollinating as a bumblebee. But it’s much more difficult to get huge numbers of bumblebees in one spot.

“So, it’s a numbers game and, based on that, honeybees will always win. But some studies have found bumblebees are ten times more efficient on a per-bee basis in pollinating a number of crops.

“Recently, bumblebees have been commercially-produced. You can purchase small hives of them. That’s become a popular thing in greenhouses, where honeybees don’t work so well. Bumblebees don’t feel the need to escape the greenhouse as much as honeybees.”

On bumblebee nesting box set-ups...

“First, I’ll be checking what type of box construction is most attractive to bumblebees. They’re very easy to build.

“The fact that bumblebees nest underground is problematic. That’s not only because it’s a pain for farmers to have to dig a bunch of holes and plant the boxes, but nesting boxes underground tend to have a lot of moisture problems. If they aren’t well-drained, that can lead to a lot of fungal problems, and can affect the developing brood.

“That’s why we’re trying an above-ground design. I’m interested to know if the bees prefer a nest tunnel or just a basic entrance — a hole in the box front. The boxes will be placed up on little legs to get them off the ground just a bit to allow some air circulation.

“I’ll also try two types of nesting material. It does tend to get very humid in the South in the spring and we need to control moisture and prevent fungal issues. We’ll try cotton fiber from recycled bluejeans and also a polyfill product that’s part bamboo rayon and part polyester.”

On previous attempts with bumblebee nesting boxes…

“Historically, when boxes have been tried, the attempts weren’t very thorough. Based on what little data are available, the occupancy rate has been very low for those boxes and no one has come up with a great design.

“I’m going to try using a large number of boxes that are about shoebox-size. Inside there’s a sort of an entrance chamber, a vestibule, which will allow the bees to defend easily, and they use it as their bathroom. On the other side of the partition is a chamber — about seven inches per side — containing a clump of nesting material.

“The first year, I’ll have 100 boxes in two different locations. The second year, after determining which design worked best, I’ll put 240 boxes on one farm.

“The farm is about 20 acres in size. I’ll see if the boxes work best around a tree line or other landmarks the bees can use for orientation. Is it best for the box to face south? North? We’ll try to answer all sorts of questions.”

Your research will apply across the South?

“Absolutely. There’s a lot of interest everywhere in native pollinators, and the species in northwest Arkansas are common throughout the South and eastern United States.

“The farms I work on are multi-crop, usually 20 acres, or less. The farmers grow something from spring through winter using fields, high-tunnels and greenhouses. 

“One of the things the study will track is which crops are in the field, the seasonality of the individual species of bumblebees moving in, and how that relates to crop bloom.

“If we have a box that works really well for a species that shows up in early spring, farmers with spring-bloom crops that need pollination help will prefer to utilize that box design to bring in the species that are more likely to show up when their fruits are blooming.”

For more, see http://comp.uark.edu/~aszalan/Apis/Bumble_Bee_Research.html.

About the Author(s)

David Bennett 1

Associate Editor, Delta Farm Press

David Bennett, associate editor for Delta Farm Press, is an Arkansan. He worked with a daily newspaper before joining Farm Press in 1994. Bennett writes about legislative and crop related issues in the Mid-South states.

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