Roughly 3 million honey bees died over a few days at the San Diego Bee Sanctuary last September.
That was about two-thirds of their overall bee population.
“All these colonies here, you just see piles of dead bees, pile of dead bees, pile of dead bees,” co-owner Dominick Peck said, recalling what it was like to find the dead colonies.
The sanctuary had two locations. Its Escondido site had to completely shut down because millions of bees were poisoned, but its Valley Center location is still operating with about 1.5 million bees.
“We can't control every single bee that's out here,” co-owner Paul Gunn said. “So all we can do is find places that are friendlier for bees and keep going.”
What both owners wanted to know was why and how so many bees died.
The County of San Diego Department of Agriculture ran tests and found the bees tested positive for a toxic dosage of Fipronil, a chemical usually used to control insects like ants and termites.
“At this point, the source of that Fipronil is undetermined,” said the county's Deputy Director of Agriculture, Garrett Cooper.
He said a bee poisoning this large is rare.
“We had surveyed a lot of the pest control businesses that provided use reports and were in the area. None of them had used that insecticide. We also looked at the ag(riculture) operations,” Cooper said.
James Nieh is an expert in studying bees and a professor of biological sciences at UC San Diego.
He said mass bee die-offs happen — in fact, Nieh said the research apiary at UCSD saw about eight colonies die around the same time.
And certain pesticides, like Fipronil, are one reason for these mass deaths.
“We have the ability to breed more bees and restore the population, but they’re very unhealthy. It's hard for beekeepers to maintain good colonies without a lot of work,” Nieh said.
The researcher said overall bee populations in the state have remained relatively stable, but when bees die, that can affect plant pollination and agricultural yields.
As for the San Diego Bee Sanctuary, the new report provides some answers, but they still have more questions.
“It's kind of nice to know what it was. It's nice to not think that it was a neighboring farm, I guess,” Gunn said.
While the investigation is closed, Peck said they plan on growing their bee population back over the coming year.
Their goal is to expand to new sites across the county, thanks to the help of financial support from the community.