In a decision dating back to September, a US appeals court in San Francisco cancelled the  registration of Dow Agroscience’s sulfloxaflor insecticide sold under the brand names Transform and Closer, saying the Environmental Protection Agency (EPA) should never have approved it.

The ruling came in response to a 2013 lawsuit filed by several organizations representing the beekeeping industry. Specifically, the plaintiffs said studies had shown the active ingredient of the insecticide – a neonicotinoid sub-class – to be highly toxic to honeybees.

“Given the precariousness of bee populations, leaving the EPA’s registration of sulfoxaflor in place risks more potential environment harm than vacating it,” the court said.

In the court’s view, said the US environmental watchdog relied on “flawed and limited data” to approve the unconditional registration. It ordered the EPA to obtain additional data on the effects of the insecticide on bees before granting renewed approval.

Dow said that while it “respectfully disagreed” with the ruling, it would cooperate with the EPA to complete the additional regulatory work to support registration.

The US Agriculture Department estimated losses of managed honeybee colonies at 42% in the year from April 2014 to April 2015, up from 34% in the 2013-2014 period.