Introduction: Imidacloprid is a neonicotinoid designed to target the nicotinic acetylcholine receptors of invertebrate insects but may affect the development of vertebrates. Nicotine is known to alter vertebrate development. Avian species may also be of particular risk of exposure to neonicotinoids from environmental pesticides and ingestion of contaminated insects and freshwater species.

Methods: We evaluated the impact of environmental relevant imidacloprid (10 µg/mL) exposure on vertebrate embryo development using a chicken egg assay and compared that with the effects of saline or nicotine exposure (0, 10 and 100 µg/mL). Research grade, specific-pathogen-free (SPF) eggs were injected on day 0 and harvested on day 14 of development. Egg weight, embryo weight and body morphometrics were compared between the treatment groups.

Results: Eggs treated with nicotine had an overall (10 - 20%) lower survival rate (P < 0.05). Embryos exposed to 10 µg/mL nicotine that remained viable at 14 days did not differ significantly from controls. Embryos exposed to 100 µg/mL exhibited reductions in limb development (P < 0.01) and altered head circumference (P < 0.009). Reductions in limb length were noted in imidacloprid exposed embryos (P = 0.054). Embryo weight was significantly reduced in the imidacloprid exposed embryos relative to controls (P = 0.034). Tissues were harvested to determine histological changes as a result of imidacloprid.

Conclusions: Evaluating the developmental impact of nicotine and imidacloprid in the chicken embryo assay highlights the potential effects of environmental exposure in poultry and other vertebrates.