A growing body of evidence suggests neonics threaten the health of honey bees. But some argue there’s not enough evidence to justify an outright ban

The most widely used class of insecticides in the world is facing a slow death. Called neonicotinoids, or neonics, these bug killers have long been used to treat millions of acres of farmland in the US.

But research showing that they sicken or kill bees and other pollinators means neonics could soon lose their grip in North America. The European Union has already temporarily banned several varieties of the insecticide and now, local and national governments in the US and Canada are moving to phase out some versions too.

The US Environmental Protection Agency (EPA), which mandated new labels for neonics with clearer language on their proper use, temporarily halted the approval of new outdoor neonics while it reviews the risks posed by five types. It expects to publish its assessments and open them up for public comment starting this year.

However, some researchers and farmers say regulatory actions are unwarranted because the problem is the unnecessary use of the pesticides as a preventive measure, and banning them would take away an effective way to protect crops.

Regulatory scrutiny of neonics already has forced major chemical companies to come up with alternatives.

Maryland is the first state to ban the use of neonics in homes and gardens, a law that will take effect in January 2018. Minnesota Governor Mark Dayton issued an executive order last August that requires farmers to demonstrate a need for pest control before using neonics. The state’s agriculture department is also looking at tightening regulations governing seeds treated with the pesticides.