Alfalfa Bees Prove Their Carrot Competence
By Marcia Wood
LOGAN, Utah, Aug. 20--The domesticated honeybee may get more glory,
but when it comes to pollinating carrots, one tiny alfalfa leafcutter bee can
do the job of 20 of its larger, noisier, more irritable cousins, says a
U.S. Department of Agriculture
Alfalfa leafcutter bees are about a quarter-inch-long, and black with bands
of white hair on the abdomen. They prefer to spend spring and summer days
gathering nectar and pollen from the purple blooms of their favorite plant,
alfalfa, said entomologist Vincent J. Tepedino of USDAs
Agricultural Research Service.
Tepedino and colleagues at the Logan laboratory investigate native bees that
can supplement or replace domesticated honeybees in fertilizing crops that
depend upon insect pollinators.
Tepedino's study was the first detailed comparison of the domesticated
honeybee and alfalfa leafcutter bee's performance as carrot pollinators in
screened enclosures. It also was the first to show that alfalfa leafcutter bee
offspring are well nourished by carrot pollen and carrot nectar. This bee
typically grows up on rations of alfalfa pollen and alfalfa nectar.
"Unlike domesticated honeybees, alfalfa leafcutter bees don't mind
working in screened enclosures or greenhouses needed for producing new kinds of
carrots, said Tepedino, based at the ARS
Bee Biology and Systematics
Laboratory here. About 150 alfalfa leafcutter bees working in
screenhouses or greenhouses would do the job as well as 3,000 domesticated
The pollination job is an essential but underappreciated part of a plant
breeders task of producing the new, more colorful or more nutritious
carrot varieties that growers and consumers want. Tepedino said his study shows
the leafcutter bees efficiency may reduce pollination costs, as well as
ease the stress on breeders and technicians who might otherwise work in cages
with several thousand honeybees.
"Domesticated honeybees can get irritable when large numbers of them
are confined in small spaces, said Tepedino. That intimidates
people. Alfalfa leafcutter bees are gentler. And they tend not to buzz around
your face or land on you like the meat flies some plant breeders now use."
Alfalfa leafcutter bees are already raised and sold commercially to
pollinate not only alfalfa but also carrots and onions in screened cages,
To produce new carrot varieties, pollen must be ferried from one variety of
parent carrot plant to another, a process known as hybridization. That means
carrot breeders must enclose the carrot plants--and the pollinating insects--in
screenhouses or greenhouses to keep out other, unwanted pollen.
Tepedino ran his experiment with both species of bees using six screened
cages, each containing 70 parent carrot plants. He found that yield of live
seed from plants pollinated by either insect was approximately the same.
Tepedino used 9,000 adult honeybees and 450 adult alfalfa leafcutter bees
for the study. He did the work with help from Asgrow Seed Company at Twin Falls, Idaho.
Alfalfa leafcutter bees are among the species scientists call "solitary
bees." These do not live in a communal nest or hive as do the familiar
honeybee. Instead, as the insects name suggests, the female alfalfa
leafcutter cuts alfalfa leaves and uses them to build a nest of snug, cell-like
compartments to house offspring.
Solitary bees, Tepedino said, aren't attacked by two kinds of mites that
have decimated many commercial honeybee colonies in this country in recent
years. Also, the solitary bees cant mate with Africanized honeybees. So
solitary bees--again unlike domestic honeybees--cant pick up the
Africanized bees' trait of extreme defensiveness and increased likelihood of
stinging people and animals.
Scientific contact: Vincent J. Tepedino, ARS Bee Biology and
Systematics Laboratory, Logan, Utah 84322-5310. Telephone: (801) 797-2559, fax