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Bee Bugs
May 27, 1999
Varroa mite on bee back.
image courtesy Scott Camazine, Penn State University

The popular view of bees conjures up images of rich honey dripping off wax combs secreted in a tree hollow. But in the last decade, the wild honeybee population has been decimated, victims of a devastating parasitic mite. Managed bees, those cared for by professional or hobbyist keepers, have also suffered heavy losses. The culprit? A tiny parasite called Varroa jacobsoni, or simply Varroa.

"It’s considered the most serious threat to beekeeping," says Nick Calderone, a bee researcher at Cornell University," in the past ten years half of the beekeepers have gone out of business."

And with the loss of the wild bees, managed bees have become crucial to our food supply. "The honey bee in the United States contributes five to fifteen billion dollars worth of agricultural commodities each year," Calderone says.

How Can Something So Tiny Cause So Much Damage?

Varroa is a reddish-brown, oval arachnid measuring approximately 1 mm by 1.5 mm, and visible to the naked human eye. It’s believed the mites were accidentally imported from Asia in 1987. Scientists say more research is needed to understand precisely how the mites kill off the colonies. "We know that they seem to be associated with a number of viruses," says Calderone, "but the exact sequence is still unknown."

Varroa micrograph.
Image: Scott Camazine, Penn State University

Although Varroa mites prefer the immature (brood) bee, they will readily attach themselves to an adult bee until larvae are available. Once the mites reach their helpless prey, the real damage begins. The female mites must feed from larval hemolymph, the bee’s equivalent of blood, to enable her to lay eggs. Robbing the larva of hemolymph causes defects in adults, such as malformed wings.

"A lot of the adult bees you see in heavily infested colonies lack wings or have very deformed wings," Calderone says. "A lot of them can’t fly even if they have wings."

The bee’s defenses against microbial invasion are also weakened. Calderone notes that bee colonies infested with Varroa usually die "within three to four weeks."

Are Pesticides the Answer?

Bees pollinated this cucumber field.
image: Nick Calderone

Beekeepers currently rely on the pesticide Apistan to curb Varroa infestations. Apistan is ideal for bee colonies, as it has a very low toxicity level to mammals. But recent reports show the mites are becoming resistant to it.

Because bees are a critical component of agriculture, the Environmental Protection Agency has approved a more powerful and potentially toxic pesticide, Cumophos , to battle the mites. "Cumophos is not the long term solution," Calderone says, "because EPA is trying to reduce the use of organophosphates and new uses are scrutinized very carefully. Cumophos is a little bit more toxic to mammals."

The search for alternatives to pesticides is keeping scientists as busy as bees.

Smoke and Screens

Calderone’s team stumbled upon one alternative mite control method while devising a means to catch some of the parasites for testing. A simple screen device allows mites that detach from the bees naturally to leave the colony, but not return.

This is augmented by the use of essential oils, such as eucalyptus, in the smoke smudges beekeepers use to mellow their hives. The oil smoke/screen method is hoped to be a cost-effective, non-chemical means of controlling the mites.

Researchers at the United States Department of Agriculture are focusing on formic acid, a natural fumigant. Calderone says formic acid controls Varroa reasonably well; what’s needed is a better delivery system. Because the formic acid evaporates so quickly, it is too costly and labor-intensive for many beekeepers. But USDA scientists are now working to perfect a gel form of the fumigant. "Formic acid also works very well against tracheal mites which is the other parasitic mite that has affected the industry in the last decade," Calderone says.

Some scientists, though, are searching for a genetic answer to the mite infestations.

Breeding the Better Bee

Marla Spivak and her team at the University of Minnesota Extension Service have investigated the breeding of ‘hygenic’ bees. These bees sweep through the colony, flushing out infested larvae, and increasing the health of the but they still require some chemical control of the mites," Spivak points out. "The aim is to use no pesticides."

The Buzz on Bees

Bees are among the planet’s most social creatures. The bee colony is highly structured, with each member born to its tasks.

  • The queen is the heart of the colony; she is tended by workers, and lives to mate and lay eggs.
  • Workers construct the honeycomb, guard the hive, and collect and process nectar into honey.
  • Drones are males whose only task is to mate with the queen, after which they die.

Bees engage in intricate dances to indicate where pollen can be found; indeed, they are one of the few species who dance.

For thousands of years, humans have delighted in bees’ delicious honey, and used the wax combs in a variety of ways. The beehive has long been regarded as a symbol of prosperity, and beekeeping has been popular for hundreds of generations.

Elsewhere on the Web

Bee Culture Magazine

Iowa State University Beekeeping Links

Scott Camazine, Penn State University



by Rogene M. Eichler West


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