Neonicotinoids and the Environment

Wild bumblebee populations are affected by neonicotinoid pesticides. Carl D. Walsh/Aurora/Getty

What Are Neonicotinoids?

Neonicotinoids, neonics for short, are a class of synthetic pesticides used to prevent insect damage on a variety of crops. Their name comes from the similarity of their chemical structure to that of nicotine. Neonics were first marketed in the 1990s, and are now used widely on farms and for home landscaping and gardening. These insecticides are sold under a variety of commercial brand names, but they are generally one of the following chemicals: imidacloprid (the most common), dinotefuran, clothianidin, thiamethoxam, and acetamiprid.

How Do Neonicotinoids Work?

Neonics are neuro-active, as they bind to specific receptors in the insects’ neurons, impeding nerve impulses, and leading to paralysis then death. The pesticides are sprayed on crops, turf, and fruit trees. They are also used to coat seeds before they are planted. When the seeds sprout, the plant carries the chemical on its leaves, stems, and roots, protecting them from pest insects. Neonics are relatively stable, persisting in the environment for a long time, with sunlight degrading them comparatively slowly.

The initial appeal of neonicotinoid pesticides was their effectiveness and perceived selectivity. They target insects, with what was thought to be little direct harm to mammals or birds, a desirable trait in a pesticide and a significant improvement over older pesticides which were dangerous for wildlife and people. In the field, reality proved to be more complex.

What Are Some Environmental Effects of Neonicotinoids?

  • Neonics disperse easily in the environment. Liquid applications can lead to runoff, planting treated seeds blows the chemicals in the air. Their persistence and stability, an advantage in fighting pests, makes neonics last a long time in soil and water.
  • Pollinators like bees and bumblebees come in contact with the pesticides when they consume nectar and collect pollen from treated plants. Neonic residues are sometimes found inside hives, inadvertently tracked in by bees. The pesticides’ indiscriminate effects on insects make the pollinators collateral victims.
  • Neonics may affect pollinators effectiveness. A 2016 study revealed that bumblebees exposed to thiamethoxam were less effective at pollinating certain plants compared to control bumblebees.
  • Domestic honeybees are already highly stressed by parasites and diseases, and their sudden recent decline has been a great cause for concern. Neonicotinoids are probably not directly responsible for Colony Collapse Disorder, but there is increasing evidence that they play a part as an additional, toxic stressor to bee colonies.
  • Wild bees and bumblebees have long been in decline due to habitat loss. Neonics are toxic to them, and there are real concerns that the wild populations suffer from this pesticide exposure. Much of the research on the effects of neonics on bees has been done on domestic bees, and more work is needed on wild bees and bumblebees, which play a crucial role in pollinating both wild and domestic plants.
  • Neonics are perhaps less toxic to birds than the older generation of pesticides they replaced. However, it appears that the new chemicals’ toxicity to birds has been underestimated. For many bird species, chronic exposure to neonics leads to reproductive impacts. The situation is worst for birds feeding directly on coated seeds: the ingestion of a single coated corn kernel can kill a bird. Infrequent ingestion can cause reproductive failure.
  • Birds that are not seed-eaters are also affected. There is evidence that insectivorous bird populations are experiencing significant declines due to the effectiveness of neonicotinoid pesticides on a wide range of invertebrates. With their food sources thus reduced, the survival and reproduction of insect-eating birds is affected. The same pattern is observed in aquatic environments, where pesticide residues accumulate, invertebrates die off, and aquatic bird populations decline.

Neonicotinoid pesticides have been approved by the EPA for many agricultural and residential uses, despite serious concerns from its own scientists. One potential reason for this was the strong desire to find replacements for the dangerous organophosphate pesticides used at the time. In 2013, the European Union banned the use of many neonics for a specific list of applications.