A methylene chloride extract of the spice, cinnamon, Cinnamomum aromaticum Nees, was shown to be insecticidal to Tribolium castaneum (Herbst) and Sitophilus zeamais Motsch. The contact, fumigant and antifeedant effects of cinnamaldehyde were tested against 2, castaneum adults and larvae and S. zeamais adults, T. castaneum and S. zeamais adults showed similar susceptibility to the contact toxicity of cinnamaldehyde, both having an LC50 of 0.7 mg cm(-2) and an LC95 of 0.9 mg cm(-2), However, cinnamaldehyde had a higher level of fumigant toxicity to T. castaneum than to S. zeamais, with LC50 values of 0.28 and 0.54 mg cm(-2), respectively., and LC95 values of 0.32 and 1.78 mg cm(-2), respectively, T. castaneum adults were more susceptible than larvae to the contact and fumigant actions of cinnamaldehyde, The larvae became less susceptible to both contact and fumigant toxicity of cinnamaldehyde with age, A flour disk bioassay using no-choice tests was employed to study the antifeedant activity of cinnamaldehyde against the insects and effects on consumption and utilisation of food by the insects, Cinnamaldehyde had no significant (P > 0.05) effects on diet consumption and growth of T. castaneum adults and had no antifeedant action against them at concentrations of up to 13.6 mg g(-1) food, However, this compound significantly (P < 0.05) reduced food consumption, growth and dietary utilisation in T. castaneum larvae, and had obvious antifeedant action against the larvae at concentrations of 27.2 and 54.4 mg g(-1) food. For S. zeamais adults, it only significantly (P < 0.05) reduced food consumption at a concentration range of 6.8 to 13.6 mg g(-1) food, but had no significant (P > 0.05) effects on the insects' growth and food utilisation. Antifeedant action was observed to increase with increasing cinnamaldehyde concentrations. The combined contact, fumigant and antifeedant properties of cinnamaldehyde make it a potentially useful grain protectant, (C) 1998 Elsevier Science Ltd. All rights reserved.
