Effects of the duration and timing of dietary methyl parathion exposure on bobwhite reproduction

Abstract

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.

Effects of Dietary Methyl Parathion on Northern Bobwhite Egg Production and Eggshell Quality

“…As observed by Bennett et al [3], short-term dietary exposure to methyl parathion had a rapid impact on bobwhite food consumption, egg production and eggshell quality. Reductions in egg production were observed after 3 to 4 d of treatment for hens exposed to greater than 20 ppm.…”

“…These protocols recommend 10 weeks of dietary pesticide exposure prior to egg laying where wild birds may be subjected to continuous or repeated exposure. There is a need to determine appropriate durations of exposure for more realistic avian reproduction tests involving OPs and carbamates [3]. There is a need to determine appropriate durations of exposure for more realistic avian reproduction tests involving OPs and carbamates [3].…”

“…sure period (25-week exposure) and a three-week exposure period (insecticide introduced during egg laying), dose-related effects were detected in eggshell quality in the three-week exposure test that were not detected in the long-term test [3]. Most published avian reproduction tests involving an OP have identified effects on egg production [3,5-91 and a few short-exposure studies have also identified effects on shell quality [3,10].…”

“…Dietary concentrations of methyl parathion were selected to complement a previous bobwhite threeweek exposure reproduction test [3]. Dietary concentrations of methyl parathion were selected to complement a previous bobwhite threeweek exposure reproduction test [3].…”

Utility of organophosphorus hydrolase for the remediation of mutagenicity of methyl parathion

“…The toxicity of MP is primarily associated with the inhibition of cholinesterase activity [4–7], which may lead to death of exposed organisms. A reproductive inhibition of MP was also reported with avian models [8,9]. Methyl parathion was reported to exhibit estrogenic activity in yeast and trout he‐patocyte aggregate cultures [10].…”