Quantitative structure-activity studies of benzoylphenylurea larvicides: III. Effects of substituents at the benzoyl moiety

Abstract

The larvicidal activity of 2-substituted- and 2,6-disubstituted-(4-chlorophenyl)ureas against rice stem borers ( Chilo suppressalis) and silkworms ( Bombyx mori) was measured by topical application under conditions in which oxidative metabolism was eliminated using piperonyl butoxide. The substituent effects at the benzoyl moiety on the activity were analyzed quantitatively using physicochemical parameters and regression analysis. The substituent parameter for the electron withdrawal from the side chain was estimated taking into consideration the steric inhibition of the resonance of ortho substituents. The results indicated that the larvicidal activity was enhanced by electron-withdrawing and hydrophobic substituents and lowered by bulky groups. The effect of substituents at the benzoyl moiety on activity was about the same for rice stem borers and silkworms. In vitro inhibition of the same series of compounds against new cuticle formation was also measured using cultured pieces of integument of diapause larvae of the rice stem borer. In vitro activity was linearly related to in vivo activity after allowing for the hydrophobic factor that may contribute to transport.