Abstract
Over the past decade, abnormalities have been documented in white-tailed deer (Odocoileus virginianus) in west-central Montana. Hypotheses proposed to explain these anomalies included contact with endocrine disrupting pesticides, such as imidacloprid. We evaluated the effects of imidacloprid experimentally at the South Dakota State University Wildlife and Fisheries Captive Facility where adult white-tailed deer females and their fawns were administered aqueous imidacloprid (an untreated control, 1,500 ng/L, 3,000 ng/L, and 15,000 ng/L). Water consumption, thyroid hormone function, behavioral responses, and skull and jawbone measurements were compared among treatments. Additionally, liver, spleen, genital, and brain imidacloprid concentrations were determined by an enzyme-linked immunosorbent assay (ELISA). Results indicated that 1) control deer consumed more water than treatment groups, 2) imidacloprid was present in the organs of our control group, indicating environmental contamination, 3) as imidacloprid increased in the spleen, fawn survival, thyroxine levels, jawbone lengths, body weight, and organ weights decreased, 4) adult female imidacloprid levels in the genitals were negatively correlated with genital organ weight and, 5) behavioral observations indicated that imidacloprid levels in spleens were negatively correlated with activity levels in adult females and fawns. Results demonstrate that imidacloprid has direct effects on white-tailed deer when administered at field–relevant doses.
Highlights
Popularity of neonicotinoids is due to their advertised high toxicity to insects and low toxicity to vertebrates[1]
Morphological and developmental abnormalities have been documented in white-tailed deer in west-central Montana
Underbite is a characteristic of congenital hypothyroidism, which has been documented in South Dakota[23], and is nearly always associated with fetal thyroid hormone function[22], but the cause has not been empirically determined for this observation
Summary
Popularity of neonicotinoids is due to their advertised high toxicity to insects and low toxicity to vertebrates[1]. The widespread use of neonicotinoids provides numerous opportunities for exposure to non-target, beneficial species via the water, soil, and contaminated plant tissues In addition to their documented effects on beneficial insects, neonicotinoids adversely affect non-target vertebrates as well, including rats (Rattus norvegicus: reduced sperm production, reduced offspring weight, increased abortions, skeletal abnormalities, thyroid lesions, atrophy of retina, reduced weight gain of offspring, oxidative stress, and neurobehavioral deficits), mice (Mus musculus: suppressed cell-mediated immune response and prominent histopathological alterations in spleen and liver), rabbits (Sylvilagus sp: increased frequency of miscarriage and premature births), red-legged partridges (Alectoris rufa: reduced adult and chick survival, fertilization rate, and immune response), Nile tilapia (Oreochromis niloticus: extensive disintegration of testicular tissue and changes to gonads), Medaka (Oryzias latipes: juvenile stress led to ectoparasite infestation), and black-spotted pond frogs (Rana nigromaculata: DNA damage at very low concentrations)[20]. Underbite is a characteristic of congenital hypothyroidism, which has been documented in South Dakota[23], and is nearly always associated with fetal thyroid hormone function[22], but the cause has not been empirically determined for this observation
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