New Leads In Bee Disappearances

In October, researchers published a study that some believe might be the best case yet to explain the causes of CCD. “Our data suggests that two pathogens interacting together may be playing a pretty big role,” says study co-author Robert Cramer of Montana State University. The study, “Iridovirus and Microsporidian Linked to Honeybee Colony Decline,” was published in the online journal PLoS One (www.plosone.org).

The fungal pathogens Nosema apis and Nosema ceranae are identified in the study as possibly playing a role. The Nosema ceranae is a fungus that can sicken honeybees when they consume its spores. The fungus — in conjunction with a virus — seems to show a strong correlation to CCD. According to the study, invertebrate iridescent virus (IIV) (Iridoviridae) is associated with CCD colonies. Prevalence of IIV significantly discriminated among strong, failing, and collapsed colonies. In addition, bees in failing colonies contained not only IIV, but also Nosema. Co-occurrence of these microbes consistently marked CCD in: (1) bees from commercial apiaries sampled across the U.S. in 2006–2007; (2) bees sequentially sampled as the disorder progressed in an observation hive colony in 2008; and (3) bees from a recurrence of CCD in Florida in 2009.

The pathogen pairing was not observed in samples from colonies with no history of CCD, namely bees from Australia and a large, non-migratory beekeeping business in Montana. Laboratory cage trials with a strain of IIV type 6 and Nosema ceranae confirmed that confection with these two pathogens was more lethal to bees than either pathogen alone.

Study authors say their report in no way means the case is closed on CCD. Other factors like mites and other environmental stresses likely combine to cause CCD.

But, the strong correlation between CCD and the two factors described in the report give scientists a good starting point to search for possible solutions to this persistent problem that continues to threaten the honeybee population worldwide.

Why should the public care about honeybees?
Bee pollination is responsible for $15 billion in added crop value, particularly for specialty crops such as almonds and other nuts, berries, fruits, and vegetables. About one mouthful in three in the diet directly or indirectly benefits from honeybee pollination. While there are native pollinators (honeybees came from the Old World with European colonists), honeybees are more prolific and the easiest to manage for the large-scale pollination that U.S. agriculture requires. In California, the almond crop alone uses 1.3 million colonies of bees, approximately one half of all honeybees in the U.S., and this need was projected to grow to 1.5 million colonies in 2010.

The number of managed honeybee colonies has dropped from 5 million in the 1940s to only 2.5 million today. At the same time, the call for hives to supply pollination service has continued to climb. This means honeybee colonies are trucked farther and more often than ever before.
Honeybee colony health also has been declining since the 1980s with the advent of new pathogens and pests. The spread into the U.S. of varroa and tracheal mites, in particular, created major new stresses on honeybees.

Has CCD ever happened before?
The scientific literature has several mentions of honeybee disappearances — in the 1880s, the 1920s, and the 1960s. While the descriptions sound similar to CCD, there is no way to know for sure if the problems were caused by the same agents as today’s CCD.
There also have been unusual colony losses before. In 1903, in the Cache Valley in Utah, 2,000 colonies were lost to an unknown “disappearing disease” after a “hard winter and a cold spring.” More recently (1995-1996), Pennsylvania beekeepers lost 53% of their colonies without a specific identifiable cause.

Varroa mites are a major threat to honeybee health and are becoming resistant to two compounds (coumaphos and fluvalinate) used to control them. Beekeepers now have a simple assay to determine whether mites are resistant and thus ensure use of appropriate control measures.

Source: USDA