Neonicotinoid insecticides are the most widely used insecticides in the world. They are nicotinic acetylcholine receptor agonists, which bind strongly to nicotinic acetylcholine receptors (nAChRs) in the central nervous system of insects, causing receptor blockage, paralysis and death. Neonicotinoids bind more strongly to insect receptor than to those of vertebrates but birds seem to be more suceptible than other vertebrates.
Neonicotinoids are mostly used as seed dressings that dissolve around the seed, are absorbed by the plant and spread through its tissues, protecting all parts of the crop against herbivorous insects. In conventional agriculture, seed dressing has to be applied prophylactically to crops leading to a risk of an overaccumulation over the years. One of the core questions with regard to the environmental impact of neonicotinoids is whether, owing to their high solubility in water and substantial half-life, they are taken up from soil and soil water by non-target species.
Considering their strong presence in the environment, they are supposed to be responsible for the decline of bees. Although some adverse effects are known, most studies on vertebrates assess only mortality and are carried out over short periods, but it is clear that important sublethal effects are induced by much lower doses.
With this study, we aim at investigating the sublethal effects of neonicotinoids on two wild passerine birds using a network of farms throughout Switzerland. Collaborating farmers manage their farms according to three methods using contrasted amounts of pesticides: conventional, Integrated production (IP-Suisse) and organic. We will use this network of farms to investigate potential links between agricultural practices, levels of neonicotinoids found in soil, crops and natural vegetation samples on the one hand, and levels of neonicotinoids found in bird plasma, bird health (oxidative stress and levels of stress hormones) and male bird reproductive capacity (sperm quantity and quality) on the other hand.