A new study raises questions about the effectiveness of the two most popular types of agricultural pesticides, noting overreliance on the chemicals causes environmental harm while doing little to boost crop yields.
Field rotation, planting naturally resistant varieties and crop insurance are more effective than neonicotinoids and fipronil at defeating bugs, which quickly develop resistance to the pesticides, a study by the Task Force on Systemic Pesticides says.
"We were surprised to see the yields with neonicotinoids, the yields were not much higher," said Dr. Jean-Marc Bonmatin, an author of the paper published in the scientific journal Environmental Science and Pollution Research. "The overwhelming evidence of negative effects on pollinators and arthropods needs to be weighed against the pest control benefits these systemic insecticides are supposed to produce."
The chemicals, used to control insects on everything from apples and potatoes to sod and pets, have been linked to declines in pollinator and bird populations, and groundwater contamination. The pesticides are systemic and are carried to all parts of the plant, not just the surface, rendering it toxic to harmful and beneficial insects alike.
The new paper, which reviewed more than 200 studies on the topic, found use of the pesticides had little effect on crop yields because, in most cases, the threat to crops from wire worms and other pests was not high enough to justify the expense. Further, the pests quickly developed resistance to the chemicals.
"It doesn't work now; this is a very important point," Dr. Bonmatin said by phone from Paris. "The more you use insecticides, the more the pests become resistant."
Researchers found other methods of pest control are more effective and less harmful to the environment. In addition to crop rotation, these methods include planting pest-resistant crops and the purchase of insurance, which is less expensive than pesticides.
Dr. Bonmatin pointed to corn farmers in a large area of Italy who purchased crop insurance against weather, pest and animal damage for the equivalent of $5 a hectare compared with $50 a hectare for pesticides.
"Abundant information is available about the negative impacts of neonicotinoids and fipronil on the environment … However, there is a great deal of reluctance to reduce or phase out these insecticides because of fears crops may experience yield losses and hurt farmers' economies," the paper said.
Dr. Bonmatin said he believes growers continue to needlessly apply the pesticides as "prophylactics" against unknown pest damage because they are advised to by seed sellers and chemical companies.
"But if we explain to the farmers that they are losing money, maybe they will follow another way," he said.
Several previous studies have shown the pesticides are highly toxic to insects and linked to declines in populations of pollinators, including bees. The pesticides are also persistent, meaning they break down slowly and accumulate in soil, surrounding pastures and groundwater.
The Canadian government is phasing out the use of one type of neonic, imidacloprid, because aquatic insects face "harmful" levels of the chemical in rivers and ponds. Health Canada has proposed restrictions on some uses of the two other most popular neonics, clothianidin and thiamethoxam.
The European Union has banned the use of all three of these popular neonics since 2013. A continued moratorium on their use is expected to go to a vote by member states in 2018.
The paper's authors said they studied neonicotinoids and fipronil because they together hold the largest share of pesticides used around the world.
But they cautioned that other pesticides pose threats to the environment and public health. "Regulators should realize that a more restrictive regulatory framework is required for more sustainable agricultural practices … with a strong willingness to use highly toxic pesticides only as a last resort."