Plant Palette

Plant Palette

Honeybees and Colony Collapse Disorder

Photo of Jennifer Schultz Nelson

Jennifer Schultz Nelson
Extension Educator, Horticulture
jaschult@illinois.edu

In considering the benefits of fruit and vegetable gardening, one of the more social and environmental aspects often touted is teaching children where their food comes from. But believe me, there are plenty of adults and kids alike that think our food comes from the store, and have never considered that someone had to grow that food somewhere.

Even if you know about growing fruits and vegetables, and know that the squash or apple you just purchased did at one time grow on a plant, chances are you never considered honeybees to have been part of the process. In fact, much of fruit and vegetable production depends on this tiny insect to pollinate individual flowers.

In theory at least, there are a lot of insects out there besides honeybees that can pollinate flowers. Some scientists estimate that three-fourths of the world's plants require assistance from an insect to pollinate their flowers. Unfortunately, many parts of the world are experiencing a population decline in native pollinators.

This may seem insignificant, but many of the fruits and vegetables we enjoy and expect to be available to us depend on insect pollinators. Honeybees are particularly adapted for gathering pollen, so they are widely used as pollinators in large plantings of crops requiring insect pollination.

Common, or Western honeybees, Apis mellifera, are considered by many to be domesticated insects. They originated in Africa, and spread across Europe and Asia. European colonists brought them to the New World, primarily as a source of honey and wax. Native Americans called them the "white man's fly". May Berenbaum, entomologist from the University of Illinois at Urbana-Champaign, referred to them as "six-legged livestock" in a statement she made to the U.S. House of Representatives this spring. Honeybees provide humans with honey and wax, but more importantly they pollinate major food crops.

Cornell University has estimated the value of crops pollinated by honeybees to be about $14.6 billion dollars each year. To put it in different terms, Zac Browning, vice president of the American Beekeeping Federation, estimates that "every third bite we consume in our diet is dependent on a honeybee".

With declining populations of native pollinators and increasingly large fruit and vegetable plantings needing pollination, many farmers rent pollination services from beekeepers while their crop is in flower. This involves placing beehives strategically around the fields so the honeybees can go to work collecting pollen and nectar for their hives, pollinating the crop's flowers along the way.

While you may picture in your mind the idyllic lifestyle of a solitary beekeeper with his handful of happy beehives, commercial use of honeybees for pollination is big business. It is not uncommon for hundreds of hives to be transported via semi-truck across country to meet the needs of large farms and major fruit and vegetable growing regions of the U.S. The biggest demand for honeybees is among almond growers–some estimate that more than half of the U.S. honeybee population is transported to California's almond groves as they flower each February.

Both honeybee and native pollinator populations have declined in recent years. Much of this has been attributed to factors such as environmental change, disease, and exposure to insecticides. Until recently, two types of mites, tracheal and Varroa, were blamed for much of the decline in managed honeybee populations. Both mites feed off the honeybee's bodily fluids, and Varroa mites are known carriers of several harmful viruses. Treatments exist for both types of mites.

In late 2006, beekeepers on the East Coast of the U.S. began reporting disappearance of large numbers of established honeybee colonies. Unlike typical disease or cultural problems associated with bee hives, there were little or no dead bees, just empty hives.

Other particularly strange symptoms observed were that in each case there was still food stored in the hive, and immature young in the hive. It would be like a person disappearing and leaving behind all their worldly belongings plus their kids!

In years past, beekeepers had occasionally described similar symptoms, calling it names like disappearing disease, fall or spring dwindle, or May disease. But no one ever knew what caused it. Besides, it occurred so infrequently and in small numbers that no one had real reason to pursue the question.

The empty hives discovered late last year were in far greater numbers than ever seen previously. As 2007 dawned, more and more beekeepers found empty hives. So far, beekeepers in 24 states have reported disappearing bees. Some large-scale professional beekeepers have reported up to 70% of their hives empty. What happened to all the honeybees? It appears that the bees left the hive and never returned, most likely dying somewhere in the landscape.

This phenomenon has been named Colony Collapse Disorder (CCD). At this time, researchers have named several likely suspects, but have yet to unravel exactly what causes CCD.

In trying to pinpoint the cause of CCD, researchers have of course taken samples of the occasional bee found in a hive stricken by CCD to look for a physical cause of the disorder. They have also begun extensive interviewing of beekeepers, trying to pinpoint some common thread in how they manage their honeybee populations. To date, only one factor has been found common to all honeybee colonies with CCD: stress.

Beekeepers noted "extraordinary stress" in each of their CCD affected colonies, usually related to drought or nutrition, prior to the total collapse of the colony. One working hypothesis for CCD is that prolonged stress is weakening the honeybees' immune system, making them susceptible to infection and disease.

Researchers at Penn State have looked at samples of live and dead bees from colonies affected by CCD and found some evidence of known bee-pathogens in the samples, but none at a level believed to cause symptoms. They also found physiological evidence that the bees' immune systems had been responding to a pathogen. Could CCD be caused by some never-before-seen pathogen? That remains to be seen.

Another possibility is exposure to sub-lethal levels of insecticides in the environment. A chemical being studied extensively is imidacloprid, a systemic insecticide which has become very popular in the U.S., particularly because it is an effective treatment for Japanese Beetles that seem to devour everything in our landscape each summer.

The systemic nature of imidacloprid is very convenient for farmers and homeowners, but in many plant species the chemical is translocated not only to the stems, leaves, and flowers, but also the nectar and pollen, which honeybees collect. Research has shown termites exposed to low levels of imidacloprid develop immune system failure and become disoriented. Could the same thing be happening to the honeybees? At this time it seems plausible, but more research is certainly needed.

Complicating the process of identifying the cause of CCD is the very real possibility that there may be a combination of factors contributing to the development of symptoms. Until a specific cause is determined, researchers can only recommend that beekeepers use documented "best management" practices in maintaining the healthiest bee colonies possible. In human terms, this is basically being told to eat a healthy diet and exercise to avoid getting sick. Since no one knows yet what causes CCD, it's the best advice that can be given right now.

As with any problem with an unknown source, a few unlikely causes of CCD have surfaced. Some have suggested that GMO crops, specifically Bt corn, have brought about CCD. Research to date has not shown GMO pollen to be correlated with the development of CCD. Undoubtedly there will be more research done in the future to address this issue.

A really unlikely source of CCD that pops up in discussions is cell phone usage. A German study placed cordless phone base stations inside beehives, and noted that this may have caused the bees to become disoriented. Somehow, this got translated to several major media outlets as cell phones causing the disorientation. No research has linked cell phones to CCD, and since CCD symptoms have been recorded historically long before cell phones were even invented, this association seems highly unlikely.

Some farmers and homeowners have made conscious decisions to welcome native pollinators such as various species of mason bees and bumblebees into their landscape. Both pollinators love a wide assortment of flowers. There are many designs available using everything from wooden blocks to paper tubes to provide suitable sites for mason bees to construct their mud-walled nests in the garden where they lay their eggs for the following year. Mason bees are solitary and bumblebees live in colonies, but both are gentle and will not sting unless provoked.

The topics of pollination, honeybees, and CCD are no doubt complex and critical to the future of many crops in the U.S. If you are interested in learning more about these topics, check out the Mid-Atlantic Apiculture Research and Extension Consortium at: http://maarec.cas.psu.edu or the American Beekeeping Federation at: http://abfnet.org.

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