Brexit has kicked the hornets’ nest.

Across Europe, populations of wild bees have been declining for the past decade. It’s estimated that 75% of food crops—including fruit, vegetable, seed, nut and oil plants—depend in part on bees and other animals to pollenate them, so the fallout from this mass death is potentially disastrous.

Climate change, habitat destruction, and disease have all played a part in this decline. But the link between bee deaths and a group of pesticides called neonicotinoids (nenonics, for short) is becoming more and more clear. Now, after leaving the EU, there is a chance that Britain could reintroduce these chemical concoctions back into its agricultural fray.

Neonics were introduced in the early 1990s to replace DDT, a more toxic chemical that was commonly used in farming. Because they are so effective at killing pests that could otherwise devastate crops, nenoics are now the most widely used pesticides in the world. But they affect insects they’re not meant to target, too. When bumblebees are exposed to neonics, their brains are affected, impairing their memory and ability to forage for pollen, as well as changing the ratio of males to females in a colony and sometimes even reducing the number of queens. This doesn’t bode well for Mother Nature’s delicate balance.

With mounting evidence that neonics cause harm to these very important insects, in 2013 the European Union put a moratorium in place, banning their use for two years. At the time, the UK opposed the ban, and Britain’s National Farmers’ Union (NFU) fought to lift it by arguing it is disastrous for rapeseed farmers, whose crops are used for cooking oil. Now that the two-year period is up, the EU is currently reviewing the latest evidence to assess whether the ban should be extended. It’s expected that it will.

Given the fierce opposition to the ban from the NFU and agrochemical lobby, environmentalists are concerned that the UK will abolish the ban on neonics when it leaves the EU. With three quarters of the world’s crops relying on natural pollination and wild bee communities contributing an average of over $3,000 per hectare to the production of crops, the reintroduction of neonics could have serious implications for the UK’s rural economy, food security, and global trade—and, of course, the bees.

Neonics can accumulate in the soil for years after use, showing up in the pollen and nectar of flowers growing in field margins, hedges, and water streams.

Professor Dave Goulson, a biologist at Sussex University and founder of the Bumblebee Conservation Trust, is one of the foremost scientists researching the effects of these pesticides on bee populations. His 2012 study on this subject helped pave the way for the EU moratorium on neonics. Since then, he says, evidence on how neonics pose a serious threat to bees has been mounting.

The most conclusive of these studies was published last year, by a group of Swedish scientists who tested the effects of neonics on bees in the field. Goulson’s more recent research examines how neonics can accumulate in the soil for years after use, showing up in the pollen and nectar of flowers growing in field margins, hedges, and water streams. “Evidence for them affecting bees, I think, is beyond reasonable doubt,” Goulson says.

Crops in the UK survived for years before the introduction of neonics, and they can continue to strive without them. After learning about the potential harm they cause bees and other insects, British arable farmer Peter Lundgren willingly stopped using the chemicals on his farm in Lincolnshire, northern England, around eight years ago.

“When I talk to groups of farmers who have had damage to crops by pests that would be controlled by neonicotinoids, they are open to alternatives,” he says. “I think they know essentially that neonicotinoids’s days are numbered.” Lundgren has been doing just fine without spraying his crops with the pesticides or buying treated seeds, carefully managing his wheat, rapeseed, and barley crops by using other insects and the occasional use of less-strong fertilizers to control pests. He now campaigns on the issue.

Still, the NFU is adamant that the ban is detrimental to farmers. It argues that there has been a “dramatic” increase cabbage-stem flea beetles since the EU introduced the ban in 2013 and claim that no form of pest control other than neonics can prevent this insect from damaging valuable rapeseed crop. “Our stance on neonicotinoids seed treatments remains the same in light of current evidence,” Emma Hamer, the NFU’s senior plant advisor, said in a statement sent to Quartz. “We believe the EU-wide moratorium is ill-informed—a knee-jerk reaction from the EU Commission that is over-precautionary.”

Bee prosperity aside, if the UK decides to reintroduce neonics once it leaves the EU, it could potentially affect Britain’s standing in the global economy.

The UK exports its food and drink to over 200 countries, accounting for a trade worth $23 billion in 2015. If the UK reintroduces neonics, countries where a ban is in place might refuse to import its agricultural produce.

France, which is among the largest importers of the UK’s agricultural produce, is moving towards introducing a total ban on neonics that goes beyond the EU’s ban on three kinds of the pesticide. The Canadian province of Ontario and the American state of Minnesota have also been suggesting a neonics ban. “As farmers we need to be careful—a bonfire of the regulations might mean that we end up in a position where we can’t trade with the rest of the world, let alone Europe,” Lundgren says.

With so many uncertainties over how, when, and even if the UK will leave the EU, at this point it is only possible to speculate over what Brexit could mean for bees. But with such bitter divides raging, it seems possible that the bees who had no say in the vote could be the ones forced to buzz off.