The decline of honey bees and other pollinators may not be a new phenomenon
By Marion Ellis
During 2006 a U.S. National Research Council panel led by entomologist May Berenbaum warned of a looming pollination crisis if honey bees and other pollinators continued to decline in number. In 1940 there were five million colonies managed by U.S. beekeepers and an abundant population of wild honey bees. In 2006 there were 2.5 million colonies managed by beekeepers and very few wild honey bees. Reasons for the decline in honey bee numbers include shifts in farming practices, changes in land use patterns, extensive use of herbicides and insecticides, low honey prices due to global trade in honey and introduced diseases and parasites. Among the diseases and parasites, the varroa mite has been the most devastating, eliminating most wild colonies and challenging the management skills of beekeepers (Fig. 1).
As if taking their cue from Berenbaum’s panel, in 2007 numerous U.S. beekeepers reported severe losses for which there was no obvious explanation. The losses were characterized by a rapid loss of adult bees from colonies, leaving a queen, a few young bees and much more brood than could be cared for in the colonies (Fig. 2). The adult bee loss ultimately resulted in colony death, and, without an obvious culprit, scientists named the problem “Colony Collapse Disorder (CCD).” The problem was first reported in January 2007 by beekeeper David Hackenburg who lost 85 percent of his 3,000 colonies. A subsequent national survey conducted by Bee Alert Technology in Missoula, Mont., found that 29 percent of the 557 beekeepers responding to the survey had experienced unexplained losses of up to 75 percent of their colonies during the past 16 months. The losses were characterized by the rapid loss of adult bees from affected colonies; however, as of yet, no one has observed a mass exodus of bees from an affected colony. Also of note, some beekeepers have been profoundly affected while their neighbors remain unscathed. The story of the bee losses has all the characteristics of a good mystery except a villain.
A National Working Group led by Jeff Pettis (USDA Bee Research Laboratory, Beltsville, Md.) was organized to address the problem. Their first challenge was to narrowly define the symptoms of CCD and to separate it from other losses that are explainable. To date, there is no evidence to support a single culprit; however, there is considerable evidence that multiple factors are stressing honey bee colonies, including bee diseases and parasites, agricultural insecticides, changes in agricultural practices, the need to move bees more frequently, severe weather and narrowing of the genetic base.
The movement of people and goods around the world in a global economy increases the risks of introducing new diseases and pests. In 1984 and 1987 tracheal and varroa mites, respectively, were first found in the United States. Both introductions caused severe colony losses. In addition to their feeding damage, these mites are thought to both vector and activate some of the 15 honey bee viruses that have been identified. Another concern is pesticides applied to crops visited by bees. U.S. beekeepers are especially concerned about imidacloprid, a systemic crop protection chemical that was banned in France in 1999 after beekeepers experienced colony losses and population decline when bees foraged on treated sunflowers. The loss of so many colonies has also given rise to many explanations not supported by evidence, such as suggestions that cell phones are interfering with the bees’ navigational system.
After five months of investigation some bee scientists, including Nicholas Calderone of Cornell University, are not convinced that what is happening is really a new phenomenon. In the 1960s and 1970s beekeepers experienced similar losses due to a condition that was called “disappearing disease,” and an 1897 article in a beekeeping journal describes healthy hives collapsing within a week with the queen still present. While the fact that some recent losses are unexplained may not be a new occurrence, what is new and concerning is the number of affected beekeepers and colonies.
One factor on which most scientists agree is that the movement of 1.2 million colonies of honey bees into the central valley of California each year for almond pollination exacerbates the spread of bee diseases and pests when the bees are subsequently returned to their home state. Almonds are California’s leading agricultural export with 580,000 bearing acres. By 2010 there will be 755,000 bearing acres, further boosting the demand for bees. Almond pollination has become an important economic engine for U.S. beekeepers, and in 2007 the dollars paid to beekeepers for almond pollination will exceed the value of the honey beekeepers produce (Figures 3, 4 and 5).
The sequencing of the honey bee genome may ultimately resolve the cause (or causes) of current and future bee losses. A recent genomic study by Cox-Foster and her colleagues in 20075 found a virus that had not previously been found in the United States, Israeli Acute Paralysis Virus
. The study also found an introduced microsporidian, Nosema ceranae
, to be widely distributed. While the study demonstrates an association of both organisms with CCD, especially the virus, it does not prove cause and affect, and most scientists remain skeptical that a single cause will be identified.
The success of honey bee colonies is tied to the quality of their environment, and when foraging conditions are poor, no amount of management can make them prosperous. Planting strips of bee forage in agricultural and urban environments can reduce the stress brought on by monocultures and urban growth. Strips of blooming plants also provide food and cover for numerous other beneficial insects, and they provide forage and cover for wildlife. Currently, many acres enrolled in conservation programs in the United States are planted to grasses and sprayed with herbicides to discourage blooming plants (Conservation Reserve Program). The addition of blooming plants and elimination of herbicide use on these acres would greatly improve the foraging opportunities for pollinating insects. In some cases CCD-affected colonies came from areas with drought or poor foraging conditions. Many scientists believe that bees in a poor nutritional state are more susceptible to diseases and parasites. Unlike other livestock, honey bees cannot be confined in large numbers and fed artificial diets for a long period of time without adverse affects on colonies. An initiative to develop a more nutritionally complete artificial diet for honey bees is being led by Gloria DeGrandi Hoffman at the USDA’s Tucson, Ariz., bee laboratory. Prior to the outbreak of CCD, a working group of beekeepers and scientists assembled at the invitation of the Foundation for the Preservation of Honey Bees to discuss research priorities, and a nutritionally complete artificial diet was identified as the number one priority.
Honey bees have been able to adapt and survive for longer than humans have been on earth. This fact is reassuring, but we need them to do more than just survive. We need them to reproduce, multiply and thrive to have the pollinators needed to service agricultural and natural ecosystems. What can concerned citizens do? Plant wildflowers, support conservation initiatives that include pollinating insects, avoid applying insecticides to blooming crops, and support research and education programs for beekeepers. The best way to conserve any organism is to increase the quantity and quality of its habitat, and augmenting the amount of foraging and nesting habitat should be incorporated in conservation programs.
While this year’s losses have been the focus of much attention, beekeepers have struggled to maintain healthy colonies for more than a decade, and serious problems need to be resolved. It appears that three major issues will need attention to resolve the chronic losses that are affecting beekeepers: (1) improve environmental quality for bees by increasing the availability of forage plants and nesting habitat; (2) improve honey bee health with research and education programs; (3) thoroughly investigate the impact of pesticides on pollinators and put appropriate restrictions on those found to cause injury.
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