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| USDA findings reveal high viral loads and mite resistance as leading causes of honeybee colony losses earlier this year. |
By Jennifer Strailey, AgWe.com
What caused catastrophic honeybee colony losses earlier this year? Researchers, scientists and beekeepers have been looking for answers since January, and now new research from the USDA’s Agricultural Research Service has identified causes behind the devastating losses.
The findings point to alarmingly high levels of viral infections — vectored by Varroa mites with resistant genes to a common treatment — as key drivers of colony collapse, according to a news release from the Honey Bee Health Coalition, a project of the Keystone Policy Center.
“I think we always thought that it would be some kind of viral load that was transmitted from the Varroa mite,” Matt Mulica, senior project director with the Keystone Policy Center, told The Packer. “As a reminder, the Varroa mite is ubiquitous across the country. On a human scale, it’d be about the size of a dinner plate, like a mite or tick. So, it’s very large compared to the size of a bee’s body.”
The study analyzed samples from six major commercial beekeeping operations affected by the losses, which collectively managed nearly 184,000 colonies — roughly 7% of all U.S. hives — and reported losses averaging over 60%, just as bees were being staged for California’s almond pollination season, according to the Honey Bee Health Coalition.
Mulica said the biggest reveal from the research was that it determined the mortality-causing viruses were Deformed Wing Virus (DWV-A and DWV-B) and Acute Bee Paralysis Virus.
All Varroa mites collected from affected colonies tested positive for a genetic marker linked to resistance to amitraz, the most commonly used miticide in commercial beekeeping, said the Honey Bee Health Coalition, adding that this finding underscores the “urgent need for new tools and integrated pest management strategies.”
Any pest is going to build resistance as beekeepers or farmers try to control it by more frequent treatments and higher doses, and that was the case here, said Mulica.
He pointed to a number of tools that beekeepers use to fight against Varroa, including coumaphos and tau-fluvalinate, which were used in the ’90s and to which eventually mites built resistance to as well.
“It’s all about rotation of chemicals and cultural techniques,” said Mulica. “Beekeepers shouldn’t be relying on amitraz as their primary mite control method. There’s a whole host of other chemicals, but also cultural techniques that they can use — re-queening and drone brood breaks (the removal of male bees from a honeybee hive to interrupt the Varroa mite life cycle and reduce mite populations), along with formic acid and oxalic acid, and some of these other new and emerging treatments.”
A Threat to U.S. Food Security
Late last month the Environmental Protection Agency, which has called Varroa mites “a national threat to bee colonies and in turn to farmers with crops dependent on pollination services provided by bees, and ultimately to food security in the United States,” proposed to register one technical and two end-use products containing the new active ingredient Vadescana — a double-stranded RNA (dsRNA) — for control against the destructive mites in honeybee hives.
“That’s really promising news that beekeepers now have even more tools to use, as these mites are becoming resistant to their primary tool, which is amitraz,” said Mulica.
The EPA further said it is prioritizing pesticide applications that target Varroa mites to provide beekeepers with a variety of tools to combat the pest.
Where Do Beekeepers Go From Here?
“Just like all epidemic epidemiological studies, there’s the controlling of the vectors of the disease, that’s the mite, and then there’s the controlling of the diseases themselves,” said Mulica. “If you remember during COVID, once they learned what it was, they immediately started working on a vaccine, and then they also had recommendations of how to avoid getting it.”
Mulica said the best practices applied during COVID are what’s happening now in beekeeping to rebuild hive strength and avoid the virus spreading to other bee colonies.
“We have tools in the toolbox that are coming out that will hopefully take the place of amitraz, so controlling the vector of the disease,” he said. “USDA is also working on antivirals. For the past 10 years, they’ve been screening hundreds of plant compounds to see what they could provide to bees that would help them heal if they got these viruses.”
Preliminary recommendations and best practices to control the virus include cleaning hive tools between use or wiping it down with isopropyl alcohol, and if someone has hives that are dwindling and not growing, know that there’s probably something wrong and keep those hives isolated, Mulica explained.
For beekeepers who have a dead colony, Mulica recommended letting it sit and air out for a few weeks before repopulating to allow the viruses to dissipate.
While these are the Honey Bee Health Coalition’s initial recommendations, the organization is working on an FAQ, currently in draft mode, that will be released in the coming weeks, he said.
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