Genomic and Behavioral Effects of the Neonicotinoid Imidacloprid in Birds Exposed Through Pesticide-Coated Seeds

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The Challenge: Neonicotinoid pesticides act as agonists of nicotinic acetylcholine receptors (nAChRs) and are designed to be lethal to insects while theoretically posing little to no threat to vertebrates. The perceived safety of neonicotinoids has led to a sharp increase in their use in the United States and globally, since they were first introduced in 1994. The use of the neonicotinoid imidacloprid in the United States has increased 166% since 2009, from 0.75 to roughly 2 million pounds, and its use as seed treatment represents approximately 56% of total annual usage. Although neonicotinoids are designed to be selectively toxic to invertebrates, effects on other organisms are being reported. However, toxicity information on birds is particularly limited. Birds are primarily exposed to neonicotinoids orally (feeding, preening), by inhalation, or dermally depending on whether the pesticide is applied by aerial spraying or as a seed coating.

The Science: To better understand toxicity mechanisms in birds, the molecular and cellular consequences of exposure to imidacloprid-treated seeds are being investigated in Japanese quail, a granivorous species often used in ecotoxicology studies as a surrogate for ground feeding birds. Because neonicotinoid pesticides are neurotoxins, they affect elements of stress response and locomotion in vertebrates. Take-off flight and escape ability of exposed quail are being studied to identify potential impacts of imidacloprid on behaviors critical for survival. Genomic analysis will identify whether nAChRs expression is altered in brains of exposed birds and which nicotinic receptor subtype is responsible for mediating any observed behavioral effects. Gene expression profiling (transcriptome analysis) is examining changes in metabolism and immune pathways.

The Future: Sublethal effects of pesticides in the field may be difficult to understand or evaluate accurately without information garnered from controlled studies. The data from this study are important for understanding how neonicotinoid use affects seed eating birds and for determining their potential contribution to declining health of various bird species. Identification of responses and mechanisms of action will facilitate characterization by managers of the risk to birds and other terrestrial wildlife from imidacloprid exposure.