U.S. honeybee numbers continue to drop, according to two new studies, with scientists blaming mite infestations while the pace of the phenomenon known as colony collapse disorder accelerated in the first quarter.
The number of commercial U.S. honeybee colonies declined 8.1 percent to 2.59 million in 2015, according to the U.S. Department of Agriculture’s first-ever honeybee health survey released Thursday. Beekeepers needed to replace 44 percent of all their hives last year to maintain insects pollinating almonds, apples and other key crops, according to a separate study published May 10 by a group of researchers.
Honeybees pollinate about $15 billion worth of crops annually, according to the USDA. Environmental groups have expressed alarm over the 90 percent decline during the past two decades in the population of pollinators, from wild bees to Monarch butterflies. Some point to a class of pesticides called neonicotinoids as a possible cause, a link rejected by Bayer AG and other manufacturers.
“There’s no question that exposure to agrochemicals is a risk factor for honeybees, but there are a lot of very complicated issues in science,” said Robert Sears, president of the Eastern Missouri Beekeepers Association in St. Louis. “That needs to be all worked out.”
In the USDA study, beekeepers who owned at least five colonies, or hives, reported the most losses from the varroa mite, a parasite that lives only in beehives and survives by sucking insect blood. The scourge, present in the U.S. since 1987, was reported in 43 percent of commercial hives between April and June last year, according to the USDA.
Losses due to colony collapse disorder -- a malady first isolated amid a spike in bee death rates a decade ago -- increased over the past year, the USDA also said. About 114,000 colonies were lost in the first three months of this year, compared with more than 92,000 in the same period in 2013.
The May 10 study released by the Bee Informed Partnership -- a collaboration between the USDA, the University of Maryland and other research and beekeeper groups -- showed bee mortality during one year at 44 percent, the second-highest level ever and almost triple the normal rate seen until roughly a decade ago. Such losses increase what farmers pay to rent bees to pollinate their crops.
For a second straight year, summer-month losses were nearly equal to winter deaths in the Bee Informed survey, a trend that diverges from traditional patterns. That could indicate weaknesses attributable to pesticides, said Tiffany Finck-Haynes, a food activist with Friends of the Earth, a Washington-based advocate for reduced chemicals use.
The U.S. Environmental Protection Agency is reviewing neonicotinoids. In January, it found that one variety, imidacloprid, may pose a risk to hives when it comes into contact with some crops that attract pollinators.
The agency has proposed bans on spraying neonicotinoids and several dozen other pesticides in fields where bees have been brought in to pollinate a crop. A White House-appointed task force called for more research on pesticide effects and meanwhile focused on improving pollinator habitats.
Bayer, the world’s biggest maker of neonics, has warned of the increased presence of varroa, which predates the introduction of its chemicals and is the biggest factor behind the increased losses, the company said in a May 10 statement. The German company is working with beekeepers to improve habitats and combat mites, it said.
The mystery of pollinator losses continues to perplex, said Dennis vanEngelsdorp, the University of Maryland entomologist who spearheads the annual Bee Informed study. Both scourges and solutions evolve, he said.
“The varroa mite we have now is not the same varroa we had 20 years ago,” he said. Also, the role of pesticides may be more complex than previously thought, perhaps by increasing the concentration of mites in hives they have already weakened, he said.
Still, the increasing amount of data and research is helping beekeepers, companies, governments and researchers better understand what actions to take, according to vanEngelsdorp.
“I think we starting to see some synergies and beginning to test new theories,” he said.