04/26/2007 - 22:00

Mother Nature’s bioterrorism

Laura H. Kahn

Laura H. Kahn

A general internist who began her career in health care as a registered nurse, Kahn works on the research staff of Princeton University's ...

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Bioterrorists, in this case Mother Nature, couldn't have picked a better target against agriculture: honeybees. Cornell University's Roger Morse and Nicholas Calderone estimate that the value honeybees contribute to U.S. agriculture through pollination grew from $9.3 billion in 1989 to $14.6 billion in 2000. (See "The Value of Honeybees as Pollinators of U.S. Crops in 2000".) The 36.3 percent increase was partly due to inflation, but the majority (around 75-80 percent) of the increase was due to a growing U.S. population's increased demand for pollinated food. Honeybees pollinate many different crops, including almonds, apples, watermelons (along with other melons), avocados, pears, cucumbers, berries, and many other fruits.

Since the end of 2006, commercial beekeepers from all over the country have reported massive die-offs of honeybee colonies. Many deaths occurred in the eastern part of the United States, but since the beginning of 2006, beekeepers from all over the country have reported significant losses. Called "Colony Collapse Disorder" or CCD, this phenomenon has the potential to devastate a significant fraction of U.S. agriculture; according to a National Research Council report, "The Status of Pollinators in North America," about three-fourths of the some 250,000 flowering plants on the planet, including most food crops, rely on pollinators for fertilization.

In her March 2007 testimony before the 110th Congress, May R. Berenbaum, head of the Department of Entomology at the University of Illinois and chair of the National Research Council Committee that issued the aforementioned report, said there have been declines in pollinators of all descriptions on no fewer than four continents over the past 20 years. The western honeybee, Apis mellifera, the world's premier pollinator species, has experienced dramatic declines largely due to the accidental introduction of two bloodsucking parasitic mites in the 1980s.

These already weakened honeybee populations are now being hit with something even more deadly. A February 2007 New York Times article stated that honeybee deaths have been reported in at least 22 states, and some commercial beekeepers have reported losing more than 50 percent of their bees. The significance of the losses can be illustrated by the numbers of honeybees needed to pollinate 550,000 acres of almond trees in California alone--about 1.4 million colonies of honeybees.

The shortage has been significant enough that for the first time since the passage of the 1922 Honeybee Act, the United States has begun importing honeybees. (The Honeybee Act banned bee imports because of fears that the bees would introduce nonnative pests.)

Other pollinators are declining, too, such as bumblebees, bats, and hummingbirds. Unfortunately, a paucity of data on the population numbers of these species exists since the United States doesn't monitor pollination services--one of the NRC report's top recommendations is to do exactly that.

There are a number of theories as to the cause of CCD, including fungal infections, environmental chemicals or toxins, stresses related to mobile pollination services, or a previously unknown pathogen. Even the use of cellular phones has been suggested. (See the Independent article "Are Mobile Phones Wiping Out Our Bees?") Joe DeRisi and Don Ganem, researchers at the University of California, San Francisco, have identified a possible suspect: a microsporidian fungus called Nosema ceranae that has been associated with infecting Asian bees.

This crisis should be a national and global priority since it seriously threatens our food supply, health, and well-being. The North American Pollinator Protection Campaign, which represents various agencies and organizations in Canada, Mexico, and the United States, has raised awareness about the issue and served as the stimulus for the NRC report. Its efforts should be supported globally because the problem isn't a uniquely North American phenomenon. According to an April 24 New York Times science article, "Bees Vanish, and Scientists Race for Reasons," countries in Europe, as well as Guatemala and parts of Brazil, have also been hit.

If the culprit does turn out to be a novel infectious disease, such as a fungus, one could speculate that CCD might be somehow related to the global die-offs we're seeing with amphibians such as frogs. Many amphibians are at the point of extinction. The most likely culprits for the global demise of amphibians are emerging infectious diseases that include chytridiomycosis, a fungal infection seen predominantly in Australia and Central America, and newly emerged viruses that infect amphibians.

The most likely explanation for the emergence of these lethal infections? Human activities. Humans probably inadvertently introduced these pathogens either directly or through habitat destruction.

For most of us, frogs are creatures of wonder. We typically don't consider their survival as critical to our own. However, this lack of concern could come back to haunt us. If CCD is a newly emerged pathogen(s), then we need to seriously address our role in the emergence and spread of infectious diseases. Even if these pathogens do not infect us directly, they could devastate our lives through the destruction of our food supply. And unless we want to spend the rest of our days eating bread, lettuce, and meat, we'd better work hard and fast on stopping the culprit of the honeybees' demise.