The US Department of Agriculture (USDA) launched an investigation in September after three million bees at the sanctuary in Northern San Diego perished in the span of just a few days, according to KPBS.
According to the findings by the agency, the bees were exposed to Fipronil, a termiticide banned for agriculture and landscaping use.
However, it remains unclear how the large quantity of bees were exposed to the substance.
“At this point, the source of that Fipronil is undetermined,” Garrett Cooper, the deputy agriculture commissioner in San Diego County, told KPBS.
“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.”
On a GoFundMe page, the sanctuary said that orchards and recreational lands within close proximity to the site did not use fipronil and that the owners suspect “malice” in the mass wipeout of the bees.
The owners have decided to close down the Escondido location, they said.
“We do suspect malice. All nearby orchards had no Fipronil. It could have been directed towards us. We cannot be sure. We are pulling out of the area,” Dominic Peck, an employee at the sanctuary, told ABC News.
The sanctuary’s Valley Center location remains open with around 1.5 million bees.