Despite a growing worldwide clamor to ban pesticides linked to honey bee deaths, multiple factors contribute to the declining honey bee population, not just one class of insecticides, says Extension Apiculturist and noted honey bee expert Eric Mussen of the UC Davis Department of Entomology.

Speaking on honey bee health at the 51st annual meeting of the international Society of Toxicology and ToxExpo, held in San Francisco, Mussen said “no specific culprit” causes colony collapse disorder (CCD), a mysterious malady characterized by adult bees abandoning the hive, leaving behind the queen, her brood, and honey and pollen stores.

Multiple factors affecting colony health include “pathogens, parasites, pesticides and malnutrition,” he told the society, which is comprised of 7,500 scientists from academia, government, and industry from various countries around the globe.

“Pesticide residues have been found in beeswax, stored pollens and adult bees,” Mussen said in his abstract.  Bee scientists are “also looking at the synergistic interactions among pesticides, including adjuvants mixed into the pesticides and investigating  everything from bacteria, fungi, viruses, malnutrition, transportation of migratory bees, impact of pollen from genetically modified plants, and effects of exposure to irradiation.”

“None of these factors explains why 25 percent of beekeepers continue to lose 40 to 100 percent of their colonies annually,” Mussen declared.

Banned in some European countries is the class of insecticides known as neonicotinoids, which act on the central nervous system of insects, Mussen said, but scientific studies show that despite the ban, the bee population continues to suffer significant annual losses.
Neonicotinoids, or systematic pesticides, are applied as seed or soil treatments, and also directly to the foliage of vegetable, orchard, field, turf and ornamental crops.

According to Mussen, colony losses are not new. Prior to the arrival of tracheal (Acarapis woodi) in 1984 and varroa (Varroa destructor) mites in 1987,  annual colony losses averaged around 5 to 10 percent, he said. “To control mites, most beekeepers place acaricides in their hives. Since then, queen longevity, colony health and vigor have declined in many operations and colony losses increased to about 15 to 20 percent.”

CCD, so-named in 2006, first surfaced in 2004 when approximately 25 percent of the nation’s beekeepers noted that apparently healthy colonies very quickly lost all adult bees, except the queen and a few newly emerged workers that soon perished, Mussen said.

“All stages of brood were present, and stores of honey and pollens were abundant,” he said. “In the few remaining adult bee specimens, titers of the fungus (Nosema ceranae) and one or more RNA viruses were very high. While appearing similar to losses induced by extremely heavy varroa mite infestations, neither bees with shriveled wings nor copious varroa fecal spots were observed.”

The resulting media attention prompted governmental agencies to provide extra funding for honey bee research. “That research provided a greater insight into the parameters of honey bee health,” he said.
 
The honey bee’s immune system is “meager” compared to that of a fruit fly or mosquito, he said.