Abstract
The mode of action of DDT and pyrethroids was investigated in the house fly, Musca domestica L., using drug:receptor binding techniques. Both in vivo and in vitro binding studies demonstrated the existence of membrane receptors in the central nervous system of house flies which specifically bind DDT and permethrin. The receptors showed properties to be expected of a critical target site of these insecticides. These include negative temperature correlation with binding, non-sensitivity to DDE and sensitivity to Ca2+. The receptor sites were saturated at 45-90 nM C('14)-DDT and have an apparent dissociation constant (K(,d)) of 12.2 nM. The number of binding sites was estimated to be 17 pmoles DDT/mg membrane protein. Competition studies showed DDT, cis-permethrin, and cypermethrin bind to the same receptor, but not precisely the same site. Target site or knockdown resistance (kdr) to DDT and pyrethroids was investigated by comparing receptor binding between susceptible (sbo) and resistant (kdr) house flies. Nerve tissue from sbo flies bound 2-3 times more DDT or cis-permethrin than tissue from kdr flies. Scatchard analysis indicated that kdr flies have the same affinity, but fewer receptors in the CNS than sbo flies. Based on these results, target site insensitivity of kdr flies is due to a reduced number of receptors for the insecticides. Similar DDT-pyrethroid receptors were detected in the tobacco budworm, Heliothis virescens (F.), and its predator, Chrysopa carnea Stephens. Receptor binding was reversible in the predator, but not the pest. This can account for the lower toxicity of pyrethroids to the predator. Chlordimeform, a known synergist for these insecticides, increased the binding of DDT and cis-permethrin to receptors in the pest. The results suggested chlordimeform is a target site synergist. The applicability of the techniques in evaluating pyrethroid selectivity and target site synergism are discussed.
Chang, Chi-Pin (1983). DDT and pyrethroids : mode of action and mechanism of target site resistance, selectivity and synergism. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -551157.