Another major bee pest is the tracheal mite, which gets inside adult bees and clogs their breathing tubes, essentially suffocating the insects. The tracheal mites also impede the bees' ability to fly, making them useless as pollinators, entomologists report.
According to Caron, both the varroa and tracheal mites lead to the death of the bees by puncturing holes in their bodies that serve as pathways for viruses. The viruses are what technically kill most of the bees, he said.
Decades of pesticide use has also taken its toll on honeybees, though farmers are beginning to refrain from pesticide applications while their crops are blooming. "People are definitely smarter than they used to be about how they apply pesticides," Kremen said.
Pest Management
Knowing that the use of pesticides, even those targeted specifically at mites, can be fraught with negative consequences, researchers are devising alternative measures to control the mites.
"Pesticides have a role. They can be very useful, but they should be down [on] the list of things we attempt," Caron said.
Toward the top of the list is the search for so-called biological control agents. One such agent scientists are looking at is a fungus that attacks mites but not the bees. However, research has yet to find a way to effectively deliver this fungus to a bee colony.
Researchers are meeting some mite-control success by increasing the ventilation of managed bee colonies. Most colonies are airtight by design, to protect honeybees from the elements. Caron likens the effect of such systems to traveling on an airplane.
"If anyone on an airplane has a cold, you are exposed to it. If they are sneezing, you have the potential to catch that cold," he said. "Bee colonies, too, are airtight. Once the pathogen is in there, it will have a better chance of spreading."
By opening colonies up to greater ventilation, Caron and his colleagues have found that the mites are less successful at reproducing. The bees can better cope with temperature fluctuations than previously believed.
Researchers are also busy combing the world's bee populations in search of bees that are resistant to—or have reduced susceptibility to—the mites. If the researchers can isolate the genes responsible for such mite-defying qualities, they could breed those genes into domestic honeybees.
"The work is very, very slow to develop those techniques," Frazier said. "And, of course, the beekeepers are desperate. If they don't use pesticides to protect their colonies, they are out of business. So, it is a real difficult situation."
Kremen's efforts are focused on augmenting the declining domesticated honeybee populations with wild bees. We'll learn more about her research in a future story.
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