Attack on one insect can have widespread impact

Some methods of killing pests are target-specific. Consider the fly swatter. It kills only what you swat.

Mousetraps kill only small mammals attracted to bait when placed in your home.

An ideal chemical pesticide would have similar target specificity. But evolution through natural selection makes that impossible.

Chemical pesticides target molecular pathways essential to life in pests, not their location in your home or field.

Molecular pathways in pest insects have descended from those of a common ancestor. Non-target organisms have the same or very similar molecular pathways, thanks to that common ancestor. These non-target organisms can include ones we value, such as pollinators.

Chemical pesticides are biocides, not pesticides.

Biocide manufacturers work to limit the range of species their products kill to just those that we perceive as pests. But they are fighting the forces of evolution. That never works out well.

The first generation of chemical biocides, including products such as DDT, was remarkably effective. But they also killed non-target species. Bioconcentration of DDT from insects — some targeted, some not — to small fish and then increasingly larger fish threatened bald eagles, which prey on fish.

The U.S. government banned most uses of DDT in 1972.

Now, we use moretargeted, less-persistent biocides, neonicotinoids, to kill insect crop pests.

“Neonics” mimic the neurological effects of nicotine. They disrupt nerve transmission in organisms, especially insects. In sufficient concentrations, they overstimulate insect nerves, causing paralysis and death.

Neonics are the most widely used biocide against agricultural pest insects in the world. In the United States, neonics are applied to almost all corn and canola crops, most sugar beet and cotton crops, and about half of all soybeans.

Suppliers coat seeds of corn, soybeans and other crops with neonics. Plants growing from these seeds incorporate these biocides in their tissue, making them toxic to pest insects. Farmers enhance this effect by spraying neonics on plants as they grow. These applications target sap-sucking and foliage-eating pest insects very effectively.

But neonics are equalopportunity biocides in terms of plant tissue that they make toxic and insects they kill. Plants incorporate neonics in their pollen and nectar, making them toxic to pollinating insects as well.

Native bees collect nectar and pollen from neonic crop plants, especially flowering ones such as canola and sunflowers, and native plants near fields growing neonic crops. Neonics spread to those native plants through the soil and dust from spraying.

The U.S. Department of Agriculture estimates that 35 percent of crop plants depend on insect pollination.

While laboratory studies show that neonics can harm honeybees, few studies under field conditions and normal neonic applications have addressed the issue, until this summer.

Two studies published in the journal Science in June reported that neonics can harm honeybee colonies and native bees foraging in or near fields growing neonictreated crops.

Insects possess common molecular pathways inherited from a common ancestral insect 400 million years ago. We may one day develop remarkably specific insecticides. Until then, an attack on one is often an attack on them all, including our pollinator allies.