Disorder associated with higher levels
of viral co-infection

By MATEUSZ PERKOWSKI

Capital Press

An epidemiological study of bee hives suffering from colony collapse disorder found no link between the mysterious syndrome and elevated pesticide levels.

Pesticide residues from 50 different chemicals were detected in several matrices -- like bee pollen, wax and the insects themselves -- but the substances were not more prevalent in afflicted hives, according to the study.

In fact, certain chemicals -- coumaphos and esfenvalerate, both insecticides -- were actually more common in hives that did not experience colony collapse symptoms, the study found.

The study was conducted by scientists from several universities in the U.S. and Belgium, as well as the USDA's Agricultural Research Service.

Though the study did not find an association between pesticides and the syndrome, researchers acknowledge the data has "notable constraints" in how some samples were collected and analyzed.

In some cases bees could have been exposed to pesticides but scientists may not have detected residues.

"Chemicals that metabolize or break down quickly may have been removed from the various matrices tested," the study said. "Alternatively, some chemicals may have been consumed (in the case of beebread) before samples were collected."

The study also did not find that afflicted hives suffered from higher levels of any single pathogen or disease, including varroa mites and Nosema parasites.

Poor nutrition also wasn't determined to play a deciding role in the disorder either, according to the study.

"None of these measures on its own could distinguish CCD from control colonies," the study said. "Moreover, no single risk factor was found consistently or sufficiently abundantly in CCD colonies to suggest a single causal agent."

Even so, afflicted hives were more likely to suffer from multiple pathogens.

For example, 55 percent of colonies with the syndrome were also infected with three or more viruses, compared to 28 percent of CCD-free hives.

Also, 34 percent of afflicted hives were infected with two species of Nosema microbe, compared to 13 percent of the colonies without the disorder.

"While no single pathogen or parasite was found with sufficient frequency to conclude a single organism was involved in CCD, pathogens seem likely to play a critical (albeit secondary) role," the study said. "CCD colonies generally had higher virus loads and were co-infected with a greater number of disease agents than control colonies."

In apiaries afflicted by colony collapse, dead or weakened hives were more likely to neighbor each other. That would indicate that a "common risk factor" or infectious agent was involved in the disorder, the study found.

Researchers acknowledged the study contained some inadvertent biases.

For example, the disorder involves bees abandoning the hive, perhaps because of an evolutionary response aimed at reducing parasites within the colony.

"An unavoidable bias that results from sampling colonies in the midst of collapse is that only surviving bees are collected," the study said. "These bees, arguably, are the least sick or most fit individuals."

The current disorder is certainly a major threat to beekeepers, but the study indicates the industry has withstood similar struggles in the past.

Since the late 19th century, about 18 international cases of "unusually high colony mortality" have been documented, including episodes in which bees displayed symptoms highly analogous to colony collapse disorder, the study found.

Staff writer Mateusz Perkowski is based in Salem, Ore. E-mail: mperkowski@capitalpress.com.