Science Magazine: The trouble with neonicotinoids

Francisco Sanchez-Bayo

Four decades ago, DDT and other pesticides that cause environmental harm were banned. Since then, newly developed pesticides have had to conform to stricter environmental standards. Yet, recent studies highlight the subtle but deadly impacts of neonicotinoids—the most widely used insecticides in the world—on ecosystems (1–3). In contrast to other insecticides, neonicotinoids are systemic, meaning that they are highly soluble and thus absorbed by the plant. They produce delayed mortality in arthropods after chronic exposure to sublethal doses but are not very toxic to vertebrates. It has taken more than a decade to unravel some of the mechanisms through which neonicotinoids affect the integrity of ecosystems. Although gaps in knowledge remain, there is a strong case for stricter regulation of these pesticides.

Neonicotinoids are mainly applied as granules into the soil or as seed-dressings during crop planting. Seeds are coated with 1 to 17 mg per kg, depending on crops and compounds. As plants grow, they take up 2 to 20% of the insecticide and distribute it to all parts of the plant, including leaves, flowers, pollen, and nectar. The resulting concentra- tions of 5 to 10 μg per liter [parts per billion (ppb)] in the sap are sufficient to control sucking and chewing insect pests (see the figure). However, pollinators such as bees, butterflies, moths, and hoverflies are equally exposed; where neonicotinoids are used, 11 to 24% of pollen and 17 to 65% of nectar is contaminated with these insecticides (3).  Read the rest.