The collapse of honey bee colonies is a phenomenon that has recently been occurring all over the world at an alarmingly increased rate, for reasons that are not entirely understood. It began in the fall of 2006, when a Pennsylvania commercial beekeeper reported severe losses of what had seemed to be thriving colonies. In the following months, beekeepers from around the U.S. reported as much as 80 to 100 percent losses of colonies. Prior to this, a normal level of colony deaths through the winter was about 10 to 30 percent.

The reason for the collapse was a mystery, as the symptoms of these losses were unlike what is seen with known disease or parasites. The colonies would be filled with bees and then a few weeks later, all of the adult bees—thousands of them—would be gone without a trace. The colony would still have honey, brood (all stages of maturing worker bees) and sometimes a live queen and a few newly emerged adult workers. These conditions were unlike any commonly seen causes of death of a colony.

With honey and pollen left, they had not starved to death. A normal response to lack of food would have been for the entire colony to flee, but the queen and all the bees would have flown away together and there most likely would have been no immature bees left behind. The presence of eggs and brood meant the queen had not failed. If it had been a killing by recent spraying of pesticide, there would have been a pile of dead bees outside the hive. If severe disease was present, it would have been seen many weeks prior.

The group of symptoms associated with a dead colony came to be called Colony Collapse Disorder (CCD). Within a few months, scientists from the U.S. Department of Agriculture (USDA), Agriculture Research Service, the Pennsylvania Department of Agriculture, the Department of Entomology, Penn State University and other agencies were hard at work gathering information and samples from dead colonies that fit this description. They took samples of the bees that were left, the honey, the wax, the pollen stored in the wax comb and other components of the hives.

The only thing all of the dead colonies had in common was Israeli Acute Paralysis virus (IBV), named so because it had first been described in Israeli honey bees. The USDA, which has a diagnostic laboratory for diseases and parasites receiving samples from beekeepers across the country, reviewed samples they had from previous years and found that IBV had been in the country for years before these events.

Scientists proposed a number of different causes: Nosema cerana, a new variety of bee dysentery that was more virulent; a new class of pesticides called neonicotinoids that was just coming on the market; cell phone signals; lack of good pollen resources; and greater impact of the serious parasite, Varroa destructor.

In the 1970s, there had been problems with a similar loss of colonies, but only in limited areas of Florida. The syndrome, called “disappearing disease” then, was finally attributed to poor quality pollen that lacked the necessary proteins for bees. Poor nutrition wasn’t the case in the most recent instances of the disappearing bees, as many of the CCD units still had large stores of good pollen in the combs that were left in the hives.

The mystery remained. Considerable research had been done on the two new parasites and a variety of studies commenced on the possible newly found causes. However, none of these agents alone, when introduced to a healthy colony, would cause the same symptoms that were seen in so many of the dead hives. The next step, studying combinations of the causes, is much more difficult and costly, but the work is ongoing.

A chemical analysis of beeswax that had been in hives for many years showed that there was a buildup in the wax of agricultural chemicals of all types. We know from studies of queen honey bees that rearing them in wax cells contaminated with miticide causes the queens to be smaller in size, weigh less and not perform as well as healthy queens when in colonies. Certainly worker and drone (male) bees raised in contaminated wax would also be affected to some extent. Some beekeepers were already removing older wax combs and making the bees produce new wax and build fresh, uncontaminated comb.

Clearly CCD is not due to a single causative agent, but is the result of the buildup of a combination of stresses in a particular colony. So, there is no simple solution. Perhaps one of the new diseases or pesticides are a major contributor, but nonetheless, it is a case of the straw that broke the camel’s back: there is one stress too many for the bees to survive.

Dr. Anita Collins is a retired Research Geneticist from USDA, Agricultural Research Service. Honey bee genetics, colony defense and alarm communication (especially in Africanized honey bees) are her areas of expertise. In addition, she has done extensive work on the cryopreservation of honey bee germplasm (semen and embryos). Currently, Collins is an Adjunct Professor of Entomology at Penn State, and is collaborating on a U.S. Geological Service survey of native bees east of the Mississippi. Her local study area is at Lehigh Gap Nature Center, where she is also President of the Board.