Panting season for corn and soybeans across the U.S. corn belt is drawing to a close. As they plant, farmers are participating in what is likely to be one of the largest deployments of insecticides in United States history.
Almost every field corn seed planted this year in the United States – approximately 90 million acres’ worth – will be coated with neonicotinoid insecticides, the most widely used class of insecticides in the world. The same is true for seeds in about half of U.S. soybeans – roughly 45 million acres and nearly all cotton – about 14 million acres. In total, by my estimate, these insecticides will be used across at least 150 million acres of cropland, an area about the size the Texas.
Neonicotinoids are very good at killing insects. In many cases they require only parts per billion, equivalent to a few drops of insecticide in a swimming pool of water.
In recent years, concerns have been raised about the influence of neonicotinoids on bee populations. As an applied insect ecologist and extension specialist who works with farmers on pest control, I believe the focus on bees has obscured larger concerns. In my view, U.S. farmers are using these pesticides far more heavily than necessary, with potential negative impacts on ecosystems that are poorly understood.
Pesticides on seeds
Most neonicotinoids in the United States are used to coat field crop seeds. Their role is to protect against a relatively small suite of secondary insect pests – that is, not the main pests that tend to cause yield loss. National companies or seed suppliers apply these coatings, so that when farmers buy seed, they just have to plant it.
The percentage of corn and soybean acreage planted with neonicotinoid seed coatings has increased dramatically since 2004. By 2011, over 90 percent of field corn and 40 percent of soybeans planted were treated with a neonicotinoid. Between 2011 and 2014, the area treated crept toward 100 percent for corn and 50 percent for soybeans. And the mass of neonicotinoids deployed in each crop doubled, indicating that seed suppliers applied about twice as much insecticide per seed. Unfortunately, many farmers are unaware of what is coated on their seeds, while others like the peace of mind that comes from an apparently better protected seed.
Unlike most insecticides, neonicotinoids are water soluble. This means that when a seedling grows from a treated seed, its roots can absorb some of the insecticide that coated the seed. This can protect the seedling for a limited time from insects. But only a small fraction of the insecticide applied to seeds is actually taken up by seedlings. For example, corn seedlings only take up about 2 percent, and it only persists in the plant for two to three weeks. The critical question is where the rest goes.
Pervading the environment
Because neonicotinoids are water soluble, the leftover insecticide not taken up by plants can easily wash into nearby waterways. Neonicotinoids from seed coatings are now routinely found polluting streams and rivers around the country.
Here it is likely that they are poisoning and killing off some of the aquatic insects that are vital food sources for fishes, birds and other wildlife. In the Netherlands, neonicotinoids in surface waters have been associated with widespread declines in insectivorous bird populations – a sign that concentrations of these insecticides are having strong effects on food webs.
Neonicotinoids also can strongly influence pest and predator populations in crop fields.