DDT and Synthetic Pyrethroids: Mode of Action, Selectivity, and Mechanism of Synergism in the Tobacco Budworm (Lepidoptera: Noctuidae) and a Predator, Chrysopa carnea Stephens (Neuroptera: Chrysopidae)1

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Abstract
Specific binding sites for DDT and cis-permethrin have been detected in the central nervous system of the tobacco budworm, Heliothis virescens (F.), and its predator, Chrysopa cornea Stephens. Competition studies indicated these insecticides compete for the same receptors, but not precisely the same site. In the tobacco budworm, binding of the insecticides to the receptors appeared to be stable. Conversely, in Chrysopa, binding of insecticides to receptors was readily reversible. The difference in receptor binding between species can be correlated with the selective toxicity of the insecticides to the tobacco budworm as compared with that with Chrysopa. Chlordimeform, a known synergist for these insecticides, significantly increased the specific binding of DDT and cis-permethrin to the receptors in the pest. The results of this study suggest a possible method to directly measure the sensitivity of insect target sites to synthetic pyrethroids, to evaluate selectivity, and to detect potential target site synergists for these insecticides against pest insects.