During her Annual Meeting lecture, May Berenbaum explained why the honeybee genome has proved to be an effective tool for learning about colony collapse disorder. | Atlantic Photography
BOSTON – For bee researchers like May Berenbaum, 2006 was the year an international consortium of researchers published the first full sequence of the honeybee genome, offering a unique and long-sought glimpse at the biological quirks of an insect that shares a productive history with humans.
It was also the year reports started surfacing about a mysterious malady devastating honeybee hives in the United States. Eventually dubbed colony collapse disorder, the syndrome set off a frenzy of research to find its cause and protect what Berenbaum called “the world’s most valuable managed pollinators.”
In her plenary address at the 2017 AAAS Annual Meeting on 18 February, Berenbaum, the department head of entomology at the University of Illinois at Urbana-Champaign, explained why the honeybee genome proved to be an unexpectedly clever tool for identifying suspects responsible for colony collapse disorder. The story of the disorder, she noted, is also the story of how the honeybee genome went from basic research to an applied science in less than a decade.
One surprise revealed by the genome work was that honeybees seemed to have a dearth of some gene families in select areas: taste, immunity and cell detoxification. The deficits do make some sense, explained Berenbaum: Honeybees usually restrict their diets to a few items — pollen and nectar — and they are scrupulously hygienic, so perhaps those gene families are not as crucial to them as others.
The genome “weak spots,” unfortunately, dovetailed with some odd twists in recent honeybee history. Berenbaum noted that commercial beekeepers feed their charges high-fructose corn syrup, douse their homes with fungicides to keep them clean, move bees across the country on trains and trucks and treat them with antibiotics.
Bees began specializing as pollen and nectar feeders and living in social groups about 60 million years ago – their ancient biology was then suddenly expected to keep pace with a barrage of changes that humans had exposed them to over just 200 years.
“The question in our minds was, ‘Does the genome in the honeybee have sufficient variation to deal with these new challenges?’” said Berenbaum.
The honeybee genome provided a wealth of data for colony collapse disorder detectives to sift through. Some of the first research on the disorder isolated signs of an unusual virus among the bee genes, but the virus was exonerated as the cause of the disorder after other scientists detected the virus in bees collected before the disorder appeared, noted Berenbaum.
Other researchers used new techniques “to compare patterns of gene expression, to determine what was stressing the bees,” said Berenbaum. For instance, they looked at whether certain genes related to immune responses or to detoxification were more active in afflicted bees, which might suggest that they were being threatened by toxins in their food or by pesticides.
Gene expression studies led researchers to find RNA fragments in the bees from viruses that are transmitted by Varroa mites, a long-time foe of honeybees that beekeepers were treating with a variety of pesticides.
“Investigations of pesticide residues commenced in the wake of colony collapse disorder and the general community was horrified to notice the extraordinary degree of contamination of honeybee hives,” said Berenbaum. Some honeybees were sickened by the pesticides and fungicides, which also hindered the growth of larvae in some cases, she said.
Berenbaum noted that commercial honeybees also eat more high-fructose corn syrup and less pollen and nectar — even as studies show that these natural bee foods increase the activity of genes involved in cell detoxification. Climate change and a landscape in the United States covered with lawns and cornfields also make it more difficult for bees to find a healthy meal, she said.
There still isn’t a definitive answer to what causes bee colonies to collapse, Berenbaum concluded, although many scientists point to a combination of viral threats, poor diet and the combination of pesticides and fungicides as the disorder culprits.
“There is not one easy solution and of all the problems, human-activities are largely responsible,” she said.
[Associated Image: Atlantic Photography]