Bee larvae tended by a worker bee. Credit: Jeff Pettis, USDA-ARS Bee Research Lab.
Three millennia ago, Romans moved honeybee hives into their orchards to improve fruit quality.
Today, we still depend on honeybees, or Apis mellifera, to pollinate more than three-quarters of flowering plants across the world, including pumpkins, blueberries, apples, avocados, and the half-million acres of almond trees in California.
But ever since the parasitic varroa mite came to the U.S. in 1987, the honeybee population has been under siege. In the last 20 years, their numbers have dropped 30 percent, according to a report released on October 18th by the National Research Council (NRC).
Now, a paper published in the Oct. 25 issue of the journal Nature is giving scientists new hope: An international team of researchers from nearly 100 institutions has sequenced the entire genome of A. mellifera, and the work may someday lead to a solution to the bees' problematic population decline.
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"It's a fortuitous time for the honeybee," said Gene Robinson, a University of Illinois entomologist who worked on the sequencing project. "The publication of the honeybee genome is providing new resources—new research tools to provide genetic studies of bee breeding and mite resistance."
Young varroa, also known as "vampire mites," hide in the cells where honeybees lay their eggs, then feed on the blood of the developing larvae. The mites weaken but do not kill their native hosts, a distinct, Asian species of honeybee, Robinson said. But when a parasite moves on to a non-native host, like the varroa did in the case of honeybees in the U.S., the host is much more vulnerable.
Robinson said the sequencing of the honeybee genome might eventually enable scientists to identify genes that are involved in resistance to mites.
"It doesn't immediately deliver results, but it provides the tools," he explained.
The decline in honeybee population comes at a time when agriculture and, consequently, the demand for pollinator is growing.
"Declines in populations of pollinators can lead to shortages that can increase production costs in agriculture, leading perhaps to increases in costs of food," said Robinson, who helped author the NRC report.
"It's a fortuitous time for the honeybee," said Gene Robinson, a University of Illinois entomologist.
Because of their complex social structure and long history of interaction with humans, honeybees are by far the most important pollinator. They pollinate a wide variety of flowers year-round, Robinson said. While a typical bumblebee colony may have only 50 individuals, a honeybee hive has about 50,000 and its members work together to forage. Honeybees are intensively "managed" by human beekeepers who rent out individual colonies to farmers.
"There's a bee industry out there that existed because of the honey at first," Robinson said, "but now it exists to serve the pollination needs of our nation's agriculture."
In the U.S. alone, he continued, honeybee pollination is a $10 to $20 billion industry.
Some individual state economies depend heavily on bee-pollinated crops. California's 500,000-acre almond crop brings in $2 billion each year and employs 20,000 people. In the next few years, the area is expected to grow to 800,000 acres, said Utah State University research entomologist Jim Cane, and the demand for honeybee colonies will increase dramatically.
But Cane said he doesn't think the sequencing of the genome will provide an immediate remedy to the honeybee shortage, and the almond farmers of California need a solution now. As part of the U.S. Department of Agriculture Bee Biology and Systematics Lab, Cane is now advising almond growers on how to have "a more balanced portfolio of pollinators" that doesn't rely so heavily on honeybees.