Scientists agree that bee colony collapse disorder (CCD) may be caused by a number of combined factors, but admit they still don't know precisely why it occurs or why it has tapered off in recent years.
The unsolved bee phenomenon has sparked intense and contentious debate within the scientific community and the public. It even garnered itself a Facebook page: Colony Collapse Disorder - Save The Honey Bees!
The disorder, first reported in 2006 and peaking in 2007, is specific, says Jeff Pettis, an entomologist who consults beekeepers on pollination health.
CCD, Pettis tells Science News, occurs when an apparently health hive loses all of its worker bees between the course of a few hours and a few weeks, leaving its queen bee, eggs and larvae to starve to death or be raided by other workers.
"It was 'OK, something weird just happened,'" recalls Jay Evans of the USDA honey bee lab in Beltsville, Maryland, when he saw the first cases more than 10 years ago. "It looked like a flu, something that kind of swept through miraculously fast."
The drastic drop-off in worker bees sparked a slew of theories as to the possible cause. Some scientists proposed it was triggered by the invasive pathogen Israeli Acute Paralysis Virus (IAPV).
Harvard University researchers theorized that CCD was the direct result of insecticides acting as nerve-poisoning agents on the honey bee workers. Other reports suggested the bees suffered as a result of varroa mites, hive beetles, Nosema fungi, and a deformed-wing virus.
Pettis was even approached by some who said the bees were disappearing because of "alien abductions… and the bees were being called home."
But as the number of "credible cases" has declined over the past five years, scientists and apiculturists have become more willing to admit that CCD isn't caused by just one thing, but is likely the result of several factors – even though their nature is as yet unknown.
Pettis says colony collapse occurs in two stages: stressors such as poor nutrition and insecticides weaken the bees' immune system, making them more susceptible to mites or IAPV, which can then kill them quickly and in droves.
Others, including the US Environmental Protection Agency, also advocate the "four Ps" theory: that poor nutrition, pesticides, pathogens and parasites are the cumulative culprits responsible for CCD.
Though colony collapse has dropped off dramatically, apiculturists across the United States still lost a third of their hives between April 2016 and March 2017.
CCD is not only damaging to hives, but also cost bee-keepers between US$8billion and $12billion between 2006 and 2007, according to the US Department of Agriculture.