Among the first to investigate the die-offs was a team of Pennsylvania State University biologists headed by vanEngelsdorp and Diana Cox-Foster. It was Cox-Foster whom beekeeper Hackenberg called the day his bees went missing.
The team started their investigation by performing autopsies on the few remaining bees in Hackenberg’s colonies. When vanEngelsdorp looked through his microscope, he was shocked: “I found a lot of different scar tissue, and [what] looked like foreign organs,” he says. There were also signs of multiple infections, including a parasitic fungus called Nosema ceranae. The bees’ insides were overrun with pathogens.
Though the bees were clearly sick, each colony seemed to suffer from a different spectrum of ailments. “The bees are getting the flu,” says vanEngelsdorp. “What we don’t understand is the fact that it’s not always the same strain of flu.” The researchers hypothesized that something had compromised the bees’ immune system, making them vulnerable to infections that a healthy colony could normally fend off. Some observers have even likened the condition to “bee AIDS.”
The analogy certainly seems fitting. But early attempts to identify a bee-equivalent of HIV (the virus that causes AIDS) were unsuccessful. The initial prime suspect, the varroa mite, was not present at high enough levels to cause a crippled immune system. And all of the other parasites and infections had previously been documented in healthy bee populations, and so were unlikely to have caused the heavy losses.
Hoping to isolate a previously unidentified culprit, in 2007, Cox-Foster and her colleagues enlisted genomics experts from Columbia University to scour genetic material from the hives for evidence of a new invader. After months of intensive work, their efforts seemed to pay off: genetic tests revealed that a virus called Israeli acute paralysis virus (IAPV) was present in 96% of the hives affected with CCD. The researchers thought they had found the smoking gun. Subsequent research, however, showed that not all honey bee colonies that are infected with IAPV have symptoms of CCD, suggesting that the virus alone is not the source of the problem.
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More recently, in 2010, researchers from the University of Montana and the U.S. Army’s Edgewood Chemical Biological Center presented evidence that another viral culprit–invertebrate iridescent virus (IIV)–was present in essentially all collapsing hives. Whether this virus proves to be the decisive factor in CCD remains to be seen. But since IIV is present in noncollapsing hives as well, it is unlikely to be acting alone.
In fact, there may be no single cause of CCD, but rather a complex combination of causes. “All the evidence so far has really supported the idea that it’s likely a combination of factors that are stressing the bees beyond their ability to cope,” says Maryann Frazier, a bee researcher at Penn State who is part of Cox-Foster’s team.
One factor that almost certainly plays a role in exacerbating the condition is poor nutrition. Just like humans, bees need a well-balanced diet that contains all the essential nutrients to remain healthy. For a number of reasons, honey bees are finding it harder and harder to obtain a nutritious diet.