Separating Agrochemicals Could Save Bees

Combining agrochemicals into one cocktail kills bees and threatens crops. There are better ways to manage pests and weeds.

What’s at stake

Many of our foods wouldn’t exist without pollinators. Bees and other insects pollinate about 400 crops or 35 percent of all produce by volume. And feed for cows and chickens contains a lot of alfalfa, which also requires pollination. Bee populations are declining alarmingly, but they don’t have to.

Ecology is complicated, and there’s no one simple cause for the problem of bee decline. Bees are stressed by agrochemicals, hunger, and parasites. Scientists used to think these causes affected bees in an additive way (one plus two is three). Researchers have found that, when it comes to the impact of agrochemicals, one plus two is often more than three.

A recent study published in Nature found that the greatest threat to bees was exposure to multiple agrochemicals simultaneously. Bees were much more likely to die when exposed to two chemicals at once than when exposed to each chemical alone. Unfortunately, “tank mixing” of agrochemicals is a common agricultural practice. Farmers often mix two or more different kinds of chemicals in a tank so they can apply them in one spraying.

“Pesticides are designed to kill insects. If a bee is exposed to one pesticide, it’s still not great,” says Harry Siviter, the lead author of the Nature study while he was at the Royal Holloway University of London. “But the chemicals amplify one another and make it worse.”

Agrochemicals’ damage to bees puts farmers in a difficult situation. Without fungicides such as azoles, farmers lose crops to fungus. But if they continue to combine azoles with other chemicals, they could destroy bee populations. Then there would be no crops to lose.

Best practices in pest management

Smarter application methods could save millions of bees—not just the obvious step of discontinuing tank mixing but a more targeted approach to applying chemicals.

The culture of farming has a norm of using agrochemicals “all the time,” says Siviter. But real-world data support a more targeted approach. In integrated pest management, farmers would use pesticides as “an absolute last resort,” not the default. It’s like going from a shotgun to a laser beam. Spraying only when necessary would save farmers money on chemicals and labor. A culture change in agriculture could benefit farmers and bees alike.

Europe offers lessons on integrated pest management. For example, scientists in Ireland study how fungus attacks wheat at a molecular level. They use this knowledge to target the timing and amount of fungicide used. Research scientist Angela Feechan, at the Earth Institute of University College Dublin, runs a project known as “Crops for the Future.” Feechan’s team, which studies a problematic wheat fungus, can predict when the fungus is about to release its spores and alert growers to spray fungicides. This approach makes fungicides more effective, reduces the volume needed, and reduces the fungus’s tendency to become resistant.

Genetic monitoring can also warn farmers when fungal pathogens mutate into a form that is more deadly to crops. Denmark operates an early warning system called RustWatch. It predicts when wheat is losing its resistance to chemicals. Then farmers can plant other strains of wheat or different crops. Prediction is essential because “by the time you see symptoms, it’s too late,” Feechan says.

There are no easy answers. Siviter emphasizes that the threats to pollinators are “ludicrously complicated.” For example, his latest work focuses on the interaction effects between climate change and other anthropogenic stressors. But steps like ending tank mixing and reducing the overall use of agrochemicals could help.