The research team, led by Ramadan D. El Shoukary of New Valley University in Egypt, exposed 320 Japanese quail chicks to oral doses of imidacloprid equivalent to one-tenth of the compound’s lethal dose for fifty percent of a population, administered twice weekly from hatch through twelve weeks of age. The birds were then tracked through their entire sexual development, from the onset of puberty through peak reproductive condition, with behavioral observations, hormone profiling, organ measurements, and genetic testing conducted at weekly intervals.

The results were striking. Treated birds of both sexes reached sexual maturity significantly later than controls, with males maturing at 44.22 days compared to 41.9 days in untreated birds, and females at 47.44 days versus 45.3 days. Exposed birds also weighed more at maturity, a paradoxical finding that the researchers attribute to disrupted metabolic and endocrine regulation rather than improved health. More concerning were the persistent reductions in the brain-somatic index and gonado-somatic index, measures of relative brain and gonad mass, which fell dramatically in treated animals and never recovered throughout the observation period.

Endocrine profiling revealed a systemic collapse of the hypothalamic-pituitary-gonadal axis, the hormonal cascade that governs reproduction. Circulating testosterone crashed in treated males, showing profound suppression at weeks ten and eleven, while total estrogens, progesterone, follicle-stimulating hormone, and luteinizing hormone were all significantly depleted in exposed birds. Notably, 17β-estradiol displayed a biphasic response, initially rising at week seven before collapsing sharply from week nine onward, a pattern the researchers suggest may reflect an early compensatory upregulation of ovarian aromatase that is ultimately overwhelmed by cumulative follicular damage and precursor exhaustion.

Behaviorally, the effects were equally dramatic. Male quails exposed to the pesticide showed severe deficits in both appetitive courtship behaviors, including chasing, waltzing, and wing flapping, and consummatory copulatory actions such as mounting and cloacal contact movements. The cloacal gland, an androgen-dependent structure essential for sperm transfer, shrank significantly, and foam production fell from 58.5 to 50.06 milligrams. In testing arenas, exposed males took longer to initiate sexual interactions, showed depressed libido scores, and completed successful matings far less frequently than controls. Crucially, the frequency of unsuccessful mating attempts did not increase, indicating that the pesticide does not merely make males clumsy but fundamentally impairs the neurological competence required to achieve copulation at all.

Female quails fared no better. Treated hens showed a profound reduction in proceptive squatting and holding-still compliance during mounting encounters, while running escape frequency remained unchanged, suggesting the pesticide selectively abolishes the neuroendocrine mechanisms driving receptive immobility rather than inducing active avoidance. Egg production collapsed across all measured parameters, with total weekly egg numbers falling from 36.8 to 31.7, egg weight dropping from 14.7 to 11.3 grams, and hen-day egg production declining from 72.7 to 62.4 percent. The researchers attribute this reproductive failure to a convergence of gonadotropin withdrawal, follicular atresia, impaired vitellogenesis, and the energetic toll of chronic sickness behavior.

Perhaps the most alarming findings came from the alkaline comet assay, a sensitive technique for detecting DNA strand breaks at the single-cell level. Liver tissue from exposed birds showed marked elevations in the percentage of DNA damage, tail length, and tail moment, reflecting the organ’s role as the primary site of xenobiotic biotransformation where imidacloprid metabolism generates reactive oxygen species. Brain tissue exhibited similarly significant genomic damage, confirming that the pesticide’s genotoxic effects cross the blood-brain barrier and directly injure the central nervous system. The researchers propose that this cerebral DNA fragmentation provides the molecular foundation for the broader behavioral and neuroendocrine collapse observed throughout the study, as oxidative injury to hypothalamic and preoptic neurons compromises the transcription of gonadotropin-releasing hormone and the neural circuitry governing sexual motivation and motor execution.

The behavioral changes also functioned as sensitive early indicators of toxicity. Exposed birds exhibited pronounced hypodipsia, drinking significantly less than controls at every evaluated week, alongside progressive increases in stationary crouching and sickness behaviors that emerged from week nine onward. Because behavioral traits are flexible, rapid responses that often manifest at lower exposure levels than structural or genetic endpoints, the authors argue that monitoring courtship and maintenance behaviors in wild birds could provide a non-invasive, cost-effective proxy for detecting neuroendocrine-disrupting contamination before populations begin to decline.

The study’s findings carry significant implications beyond the laboratory. Imidacloprid is frequently detected in agricultural soils, surface waters, and wildlife habitats worldwide, and humans are exposed through contaminated food, water, household dust, and contact with treated companion animals. Previous research has linked neonicotinoid exposure to delayed migration in songbirds and compromised energy homeostasis in game birds, and the new work extends this evidence by demonstrating that reproductive behavior itself is among the most sensitive endpoints for detecting sublethal toxicity. The researchers caution that their study was conducted under controlled laboratory conditions and did not assess hatchability or transgenerational effects, leaving open questions about whether the observed damage persists after exposure ends or is passed to offspring.

Ultimately, the authors call for integrating behavioral ecotoxicology into regulatory risk assessments, arguing that a pesticide capable of dismantling the hormonal, neurological, and genetic machinery of reproduction at one-tenth of its lethal dose poses a threat that conventional toxicological testing may systematically underestimate. As wild bird populations continue to decline across agricultural landscapes, the silent courtship of contaminated quails may be sounding an alarm that regulators can no longer afford to ignore.

Subject of Research: Neuroendocrine, behavioral, and genotoxic effects of chronic imidacloprid exposure in Japanese quails

Article Title: Sexual behavior dysfunction and sickness behavior as an early warning indicators of imidacloprid exposure, associated with pituitary–adrenal axis dysregulation and DNA damage in Japanese quails

Article References: El Shoukary, R. D., Abd El-Maguid, D. S., Abd El Kareem, A. H., Abd El-Maguid, A. S., Seddik, G. N., Khafaga, A. F., & Abdelbaeth, N. (2026). Sexual behavior dysfunction and sickness behavior as an early warning indicators of imidacloprid exposure, associated with pituitary–adrenal axis dysregulation and DNA damage in Japanese quails. Frontiers in Veterinary Science, 13, Article 1914494. https://doi.org/10.3389/fvets.2026.1914494

Image Credits: AI Generated

DOI: 10.3389/fvets.2026.1914494

Keywords: imidacloprid, neonicotinoids, Japanese quail, endocrine disruption, reproductive toxicity, DNA damage, comet assay, sickness behavior, courtship behavior, ecotoxicology, HPG axis, pesticides