Unlike other pesticides which remain on the surface of treated foliage, systemic pesticides are taken up by the plant and transported to all the tissues (leaves, flowers, roots and stems, as well as pollen and nectar).
The most common are Neonicotinoids and Fipronil (neonics), which are a class of neuro-active, nicotine-based systemic insecticide. These were developed in 1991 and brought into commercial use in the mid-1990s.
Products containing neonics can be applied at the root (as seed coating or soil drench) or sprayed onto crop foliage. The insecticide toxin remains active in the soil or plant for many months (or years), protecting the crop season-long.
Neonics act on the information processing abilities of invertebrates, affecting specific neural pathways that are different from vertebrates. This makes them popular as broad-spectrum insecticides, as they are considered less directly toxic to vertebrate species including humans.
These systemic insecticides have become the most widely used group of insecticides globally, with a market share now estimated at around 40% of the world market. Common compounds include acetamiprid, clothianidin, dinotefuran imidacloprid, nitenpyram, nithiazine, thiacloprid, thiamethoxam and fipronil, with global sales of over US $2.63 billion in 2011.
The market for seed treatments is expanding even more rapidly, growing from €155 million in the 1990s to €957 million in 2008, at which point neonics made up 80% of all seed treatment sales worldwide.
Neonicotinoids are still toxic even at very low doses. They have a high persistence in soil and water, remaining in situ for months on average, and this results in sustained and chronic exposure of non-target organisms, such as invertebrates. Because they are relatively water-soluble, they run off into aquatic habitats easily. Growing concern about their connection to bee colony collapse disorder has led to restrictions on their use in EU Countries. Concern about their impact on other non-target species including birds, has been growing for the last five years.