Evidence for Pollinator Cost and Farming Benefits of Neonicotinoid Seed Coatings on Oilseed Rape

Chronic exposure to neonicotinoid insecticides has been linked to reduced survival of pollinating insects at both the individual and colony level, but so far only experimentally. Analyses of large-scale datasets to investigate the real-world links between the use of neonicotinoids and pollinator mortality are lacking. Moreover, the impacts of neonicotinoid seed coatings in reducing subsequent applications of foliar insecticide sprays and increasing crop yield are not known, despite the supposed benefits of this practice driving widespread use. Here, we combine large-scale pesticide usage and yield observations from oilseed rape with those detailing honey bee colony losses over an 11 year period, and reveal a correlation between honey bee colony losses and national-scale imidacloprid (a neonicotinoid) usage patterns across England and Wales. We also provide the first evidence that farmers who use neonicotinoid seed coatings reduce the number of subsequent applications of foliar insecticide sprays and may derive an economic return. Our results inform the societal discussion on the pollinator costs and farming benefits of prophylactic neonicotinoid usage on a mass flowering crop.

Insects underpin the seed and fruit formation of pollinator-dependent crops that make up a critical fraction of the human diet. Since 1961, the global cultivated area of insect-dependent crops has trebled, while at the same time several key insect pollinator groups have declined. This has led to concerns that pollination deficits may limit crop production. Agricultural intensification reduces the diversity of food plants upon which insects depend and increases pollinators’ exposure to multiple pesticides that may act synergistically to increase insecticidal activity. Neonicotinoids are potent nerve stimulants with a high affinity for insect nicotinic acetylcholine receptors and include the N-nitroguanidine group (clothianidin, imidacloprid or thiamethoxam) used as seed coatings, and the less toxic N-cyanoamidine group (acetamiprid and thiacloprid) used as foliar insecticide sprays. Neonicotinoids are readily absorbed by plants, which transport them systemically providing pest protection throughout all plant tissues. The versatility of application and favourable pest control properties have contributed to neonicotinoids becoming the most widely used insecticides in the world, with over 90% of usage in the form of seed coatings of clothianidin, imidacloprid or thiamethoxam.