Age-dependent toxicity of diazinon and terbufos in European starlings (Sturnus vulgaris) and red-winged blackbirds (Agelaius phoeniceus)

Adult European starlings (Sturnus vulgaris) are more resistant to poisoning by organophosphorous (OP) pesticides than are other passerine birds. Nestling starlings, however, are sensitive to OP intoxication. Both adult and nestling red-winged blackbirds (Agelaius phoeniceus) are sensitive to OP toxicity and therefore may be a more representative model of the toxic response of passerine birds. The purpose of this study was to compare the toxicity ratio, as indicated by median lethal dose (LD50), of terbufos and diazinon in adult and nestling starlings and red-winged blackbirds, and to compare cholinesterase (ChE) inhibition between species and among age groups. Red-winged blackbirds are more sensitive to terbufos and diazinon intoxication than are European starlings, and the young of both species are more sensitive than the adults. When mortality is used as the endpoint, adult starlings are approximately 103 times less sensitive to terbufos intoxication than are 2-d-old starling chicks and 137 times less sensitive than adult red- wings. Adult red-wings were only 4.1 times less sensitive than 0 to 3-d-old red-wing chicks. Adult starlings were approximately 47 times less sensitive to diazinon toxicity than 2-d-old starling nestlings and 65 times less sensitive than adult redwings. Adult red-wings were 3.8 times less sensitive to diazinon than 0- to 3-d-old red-wing nestlings. Plasma and brain ChE activity was depressed in starling and red-wing adults in a dose-dependent fashion, but the relationship between dose, and plasma and brain ChE depression was more evident in some nestling age groups than in others. Baseline ChE activity cannot be invoked to explain the sensitivity difference between species. Baseline ChE activities in both brain and plasma increase with age in both species. These changes may account in part for the greater sensitivity of the young as compared to the adult.