Pathogen Loads Higher in Bee Colonies Suffering from Colony Collapse
Disorder By Kim
Kaplan August 12 , 2009
A higher total load of pathogens—viruses, bacteria and
fungi—appears to have the strongest link with Colony Collapse Disorder
found so far, according to a new study published by
Agricultural Research Service (ARS) and
The study was headed by Pennsylvania
State University entomologist Dennis vanEngelsdorp and entomologist
Evans and virologist
Chen with the ARS
Research Laboratory in Beltsville, Md. They looked at more than 200
individual variables in 91 colonies from 13 apiaries in Florida and California,
where many beekeepers overwinter their honey bees. Among the factors for which
the researchers screened were bacteria, mites, Nosema (protozoan
parasites), numerous viruses, nutrition status and 171 pesticides. Adult bees,
wax comb, beebread (stored and processed pollen), and brood were all
No single variable was found consistently in only those honey bee
colonies that had Colony Collapse Disorder (CCD)—a syndrome characterized
by the sudden disappearance of adult honey bees in a colony—that has been
devastating some beekeepers in the United States and other countries.
Among the colonies that had CCD, no single pathogen among those
screened had a higher prevalence. Nor was there a higher or lower prevalence of
varroa mites, tracheal mites or spores from Nosema species, nor a
higher total load of these parasites and pathogens. Nosema has been
implicated in colony die-offs in Spain, but it has not been closely associated
with CCD in the United States.
But overall, CCD colonies were co-infected with a greater number of
pathogens—bacteria, microparasites like Nosema, and viruses.
Overall, 55 percent of CCD colonies were infected with three or more viruses,
compared to 28 percent of non-CCD colonies. The researchers also found
detectable levels of residues from 50 different pesticides in all of the
sampled colonies. There was no association between increased pesticide levels
In fact, the pyrethroid insecticide Esfenvalerate, used for a wide
variety of pests such as moths, flies, beetles and other insects on vegetable,
fruit and nut crops, was more prevalent in the wax in non-CCD colonies. This
insecticide was found in 32 percent of non-CCD colonies, compared with 5
percent of the CCD colonies.
Coumaphos, which is used to treat varroa mites in honey bees, was also
found in higher levels in non-CCD colonies.
As for pathogen levels, what the study cannot show is whether the
higher pathogen load was involved in the cause of CCD or was a result of CCD,
according to vanEngelsdorp. Higher pathogen loads are likely to have caused CCD
symptoms, but what causes the bees to become infected with so many pathogens is
still not known, he added.
While the study’s results don’t indicate a specific cause
of CCD, the results do help scientists narrow the direction of future CCD
research by showing that some possible causes are less likely, added
ARS is the principal intramural scientific research agency of the
U.S. Department of Agriculture.
The scientific article can be found at
A report that summarizes research progress on CCD can be found at