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Feature

Bee mites (Varroa)

Bee mites (round red spots) are just one of many sources of stress on honeybees, whose numbers plummeted this winter.

Trouble in pollen nation

Bee shortage renews appreciation for hard-working insect

By Deane Morrison

April 11, 2007

After a long trek from Minnesota in a flatbed truck, the honeybees arriving in California's Central Valley are stressed and hungry. They don't like being crammed together with lots of others of their species, yet pollinating California's almond crop requires a million colonies worth of bees. The hard labor of honeybees usually goes unnoticed and unappreciated by most Americans, but when the bees suffered steep mortality this winter--up to 80 percent of colonies lost in some beekeeping operations--the threat to the nation's food supply sent tremors through both producers and consumers. "For large monocultures of crops, you have to have honeybees," says Marla Spivak, an entomologist with University of Minnesota Extension. "We rely on honeybees to do the big jobs. Without honeybees and other bees to pollinate crops, grocery shelves would have about one-third fewer fruits and vegetables, and many flowers would not set seed." Honeybees aren't native to the United States, but were imported from Europe as early as 1622. Representing just a few of the 3,500 or more bee species in the Americas, they tend to pollinate a wide variety of plants and produce much more honey than other species. Their high sociability allows them to be transported long distances in large hives. Besides honeybees, the United States is home to many bees that live in the ground, as bumblebees prefer to do, or in other structures such as wood.

Without honeybees and other bees to pollinate crops, grocery shelves would have about one-third fewer fruits and vegetables, and many flowers would not set seed.

Given the honeybee's crucial importance to agriculture, scientists like Spivak are hard at work trying to improve bee health. This year's devastation is worrisome in part because its cause is still unknown. In many hives, large numbers of adult bees simply disappeared without a trace, leaving larvae and pupae but no dead bodies to be examined for disease, pesticide residues or other agents. And, unfortunately, the list of factors afflicting bees is long.

Like bees? Spare those dandelions

Bees must have access to a variety of plant pollens to get all the amino acids and other nutrients they need, and weeds like dandelions, creeping charlie, and roadside plants are bee favorites. So before you spray that dandelion or rip up that nameless flowering weed, consider that you may be robbing your neighborhood bees of a food source.

One of the biggest players is, paradoxically, civilization itself. On the one hand, civilized peoples have cultivated honeybees; but on the other, urban sprawl has turned diverse native landscapes rich in clover and alfalfa into crop monocultures, houses, and pavement, destroying many sources of pollen and nectar that bees need. Another threat comes from parasitic mites, especially Varroa mites, which live on the external surfaces of both larval and adult bees. Mites, as well as bacterial and fungal diseases, spread easily among bee colonies concentrated in a small area, such as is the case during pollination season in agricultural areas. A third element is pesticides, which can sicken or kill nontarget species like bees. And even pesticides aimed at bee diseases and mites are becoming less effective as the organisms develop resistance. During the winter of 2004-05, for example, a die-off of bees occurred in part because mites became resistant to a pesticide.

A good reason to love bumblebees

If you grow juicy big tomatoes, thank the bumblebees in your neighborhood. Only they can pollinate tomatoes because the tomato plant won't release its pollen unless its pollen-making anthers (the orangish cones in the middle of the flowers) are shaken. Honeybees just roll around on the flowers, but bumblebees grasp the anthers with their mouthparts and vibrate their wings, triggering a cascade of pollen.

Whatever killed large numbers of bees this winter is most likely a combination of things that finally pushed them over the edge. "The bees' immune systems have been compromised from a number of causes," says Spivak. Yet, several factors are working in the bees' favor. New treatments reduce the risk of pests like mites or bacteria developing resistance, and people applying pesticides often choose ones that decompose quickly and have low toxicity to bees. Also, genetically modified crops have no known effects on honeybees. But, Spivak points out, "new classes of pesticides, such as those that move through plant tissue, may contribute to the stress on bees' immune and detoxification systems." Along with entomologist Gary Reuter and students, Spivak focuses her research on keeping bees healthy. In her lab, she breeds bees for hygienic behavior, a mechanism of resistance against bee diseases and parasitic mites. She and her colleagues are also researching ways to bolster the immune system of bees. For more on what the University is doing to help honeybees, visit the U of M Bee Lab Web site.