Quantitative structure-activity relationships of pyrethroid insecticides

The structure-activity relationships of two congeneric series of pyrethroid insecticides, the methylbenzyl (1RS)-cis,trans-chrysanthemates tested against Musca domestica (houseflies) and Phaedon cochleariae (mustard beetles), and the (E)-4-aryl-3-chlorobut-2-enyl chrysanthemates and their corresponding 2,2,3,3-tetramethylcyclo-propanecarboxylates tested against M. domestica only, have been examined using multiple regression analyses and substituent constants. With M. domestica, different optimum partition values (π) were indicated for knockdown and toxicity; with P. cochleariae, an optimum π value for toxicity, similar to that for M. domestica, was obtained 24 h after application, but at later times the more lipophilic compounds were more effective. For the methylbenzyl chrysanthemates, a steric constraint associated with 3,5-dimethyl substitution reduced toxicity approximately five-fold. The influence on toxicity of geometrical isomerism and electronic effects are briefly discussed. Differences between the required polarities for knockdown and toxicity are attributed to variations in the binding affinities of pyrethroid molecules at the sites of action.