Behavioral evaluation of the antifeedant effect of 10 naturally occurring 1,4-naphthoquinones on larvae of the Mexican bean beetle, Epilachna varivestis Mulsant, was undertaken concurrently with that of a series of synthetic analogs and model compounds in order to assess structure–activity relationships. Plumbagin, 1,4-naphthoquinone, juglone, menadione, and naphthazarin, which were found to be active at 0.3% concentrations, were also bioassayed at 0.1, 0.05, and 0.01% at which concentration 1,4-naphthoquinone still retained some activity. The model studies suggest that two structural features might be operative independently against E. varivestis: one consisting of a properly substituted naphthoquinone moiety and the other requiring a benzo- or naphthohydroquinone. Within the naphthoquinone group, the relative activity is determined by a substituent effect which is the outcome of a complex interplay of electronic, steric, electrochemical, and positional requirements. Among the model compounds, 2-chloro-3-amino-1,4-naphthoquinone and α-naphthylamine displayed appreciable activity even at 0.01% The results should enable selection of plant sources for naphthoquinones possessing larval inhibition properties.