EFFECT OF SUBSTITUENT AND RING CHANGES IN NATURALLY-OCCURRING NAPHTHOQUINONES ON THE FEEDING RESPONSE OF LARVAE OF THE MEXICAN BEAN BEETLE,EPILACHNA-VARIVESTIS

Behavioral evaluation of the antifeedant effect of 10 naturally occurr ing 1,4-naphthoquinones on larvae of the Mexican bean beetle, Epilachn a varivestis Mulsant, was undertaken concurrently with that of a serie s of synthetic analogs and model compounds in order to assess structur e-activity relationships. Plumbagin, 1,4-naphthoquinone, juglone, mena dione, and naphthazarin, which were found to be active at 0.3% concent rations, were also bioassayed at 0.1, 0.05, and 0.01% at which concent ration 1,4-naphthoquinone still retained some activity. The model stud ies suggest that two structural features might be operative independen tly against E. varivestis: one consisting of a properly substituted na phthoquinone moiety and the other requiring a benzo- or naphthohydroqu inone. Within the naphthoquinone group, the relative activity is deter mined by a substituent effect which is the outcome of a complex interp lay of electronic, steric, electrochemical, and positional requirement s. Among the model compounds, 2-chloro-3-amino-1,4-naphthoquinone and alpha-naphthylamine displayed appreciable activity even at 0.01%. The results should enable selection of plant sources for naphthoquinones p ossessing larval inhibition properties.