Abstract
Tolerance to DDT of a population of ring-necked pheasants (Phasianus colchicus) occupying an area to which DDT was applied for 8 years, and of a population inhabiting a nearby area with no history of insecticide use was investigated during 1966-68. Median lethal concentrations (LC5o) of technical DDT in diets of week-old chicks indicated that progeny from the unexposed population were sig- nificantly more tolerant to DDT than progeny from the exposed population (P < 0.025). Levels of tol- erance could not be explained on the basis of amounts of DDT residues passed to young through eggs, lengths of time that parents were in captivity, or to the number of generations in captivity. If DDT acted as a selective force on the population of pheasants occupying the area treated with DDT, differ- ences in tolerance of the two populations must have been greater prior to use of DDT on the treated area. Abstract: Tolerance to DDT of a population of ring-necked pheasants (Phasianus colchicus) occupying an area to which DDT was applied for 8 years, and of a population inhabiting a nearby area with no history of insecticide use was investigated during 1966-68. Median lethal concentrations (LC5o) of technical DDT in diets of week-old chicks indicated that progeny from the unexposed population were sig- nificantly more tolerant to DDT than progeny from the exposed population (P < 0.025). Levels of tol- erance could not be explained on the basis of amounts of DDT residues passed to young through eggs, lengths of time that parents were in captivity, or to the number of generations in captivity. If DDT acted as a selective force on the population of pheasants occupying the area treated with DDT, differ- ences in tolerance of the two populations must have been greater prior to use of DDT on the treated area. This is a report on levels of tolerance to DDT (nomenclature for chemical insecti- cides is that of Kenaga and Allison 1969) exhibited by two populations of ring-necked pheasants. One population inhabited an area to which technical DDT was applied annually for 8 years; the other inhabited an area which had no history of agricultural applications of chlorinated hydrocarbon in- secticides.
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