EFFECTS OF BENZENE DERIVATIVES FROM ESSENTIAL OILS ON TRIBOLIUM CASTANEUM (HERBST) AND SITOPHILUS ZEAMAIS MOTSCH

Abstract

Natural benzene derivatives, namely cinnamaldehyde, safrole, isosafrole, isoeugenol and methyleugenol, were tested for toxic and antifeedant activities on T. castaneum and S. zeamais. All of them possess contact toxicity to S. zeamais, but only cinnamaldehyde, safrole and isosafrole are toxic to T. castaneum. These three compounds also have fumigant toxicity to both species of insects. In the nutritional and antifeedant studies, the compounds generally show antifeedant activity against T. castaneum and S. zeamais. A comparison of the properties of gut amylases from the adults and larvae of T. castaneum and the effects of these compounds on the gut amylase of T. castaneum larvae were carried out in order to find out the mechanism of their antifeedant activities. The optimum temperature, Km and Vmax for the amylase from the adults are 35°C, 0.49% and 46 µmole glucose/ min/ mg protein respectively, but for the larvae, they are 37°C, 3.33% and 250 µmole glucose/ min/ mg protein respectively. Both safrole and isosafrole inhibit gut amylase activity from both larvae and adults in vitro. In contrast, isoeugenol stimulates the enzymatic activity, but cinnamaldehyde and methyleugenol did not affect amylases. However, in vivo, safrole, isoeugenol and methyleugenol inhibit the larval amylase activity, but cinnamaldehyde slightly stimulates the enzymatic activity. lsosafrole showed biphasic effects; it slightly inhibits the amylase activity at 5.4 mg/g food, but stimulates the enzyme at 10.8 mg/g food.