Two northern bobwhite (Colinus virginianus) reproduction tests were conducted concurrently to evaluate how the duration and time of initiation of methyl parathion exposure affected dose‐response relationships of reproductive parameters. In the long‐term exposure test, pairs of adult bobwhite were fed methyl parathion‐amended diets (0, 7, 10, 14, 20 or 28 ppm) for 25 weeks: 10 weeks prior to the onset of laying, 6 weeks as they came into laying condition and 9 weeks during egg laying. In the short‐term exposure test, quail received amended diets (0, 10, 14, 20, 28 or 40 ppm) for only three weeks during the egg laying period, followed by a three‐week posttreatment period. Fourteen birds died in the long‐term test, compared to two in the short‐term test. Significant dose‐related reductions in daily food consumption, egg production and the number of 14‐d‐old chicks were observed in both tests during the treatment periods. No dose‐related effects on fertility, hatch‐ability or chick weights were detected. In the long‐term test, there were dose‐related decreases in adult body weight, brain and serum cholinesterase activity and female serum calcium concentrations. Cholinesterase and calcium were not measured in the short‐term test. Eggshell weights were significantly decreased in both tests, but a dose‐related decrease in eggshell strength and thickness was detected only in the short‐term test. During the posttreatment period of the short‐term test, no dose‐related effects on reproductive parameters were observed, except that egg production did not recover until the third week after treatment. Except for the number of adult mortalities, all dose‐related effects observed in the long‐term exposure test also were observed in the short‐term test. The short‐term test design had two advantages that reduced variability unrelated to the chemical treatments: infertile and incompatible pairs could be removed from the experiment and pretreatment values could be obtained to serve as controls for each pair.
Red-winged blackbird (Agelaius phoeniceus; blackbird) and European starling (Sturnus vulgaris; starling) nestlings were dosed with either 2.0 mg/kg body mass chlorpyrifos, 50.0 mg/kg body mass dimethoate, or a propylene glycol carrier in situ. Four growth measurements (body mass, culmen, tarsus, wing) were recorded from nestlings to determine if these organophosphorus compounds caused perturbations in development at sublethal concentrations. Blackbird nestlings were more sensitive to chlorpyrifos than starling nestlings were more sensitive to dimethoate than blackbird nestlings. This was in contrast to reported adult LD50 values where the reverse was true. Blackbird nestlings were more tolerant of a substantially higher concentration of dimethoate than the adult LD50. The sensitivity of starling nestlings to dimethoate was similar to adults. In contrast, juveniles of both species were more sensitive to chlorpyrifos than adults. After the initial 24 hr, surviving nestlings dosed with either chemical recovered and continued their development. Exposure to dimethoate caused significant depression in starling body mass during the initial 24 hr period. Survivors obtain body mass equal to controls within 48 hr post dosing. The research presented here demonstrates that the simple supposition that passerine nestlings are typically more sensitive to toxins than adults does not always hold true. It also indicates that sensitivity relationships among adults do not necessarily apply to their nestlings.
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