Bioactivities of safrole and isosafrole on Sitophilus zeamais (Coleoptera : Curculionidae) and Tribolium castaneum (Coleoptera : Tenebrionidae)

Sitophilus zeamais Motschulsky and Tribolium castaneum (Herbst) adults were equally susceptible to contact toxicity of either safrole or isosafrole. S afrole also possessed equal fumigant toxicity to adults of both species. Ho wever, adults of S, zeamais were twice as tolerant as T. castaneum to the f umigant toxicity of isosafrole. In both contact and fumigant tests, 12- and 14-d-old larvae of T. castaneum showed similar susceptibility to each of t he compounds, but 16-d-old larvae became more tolerant than the younger lar vae. Isosafrole was generally more toxic than safrole to the insects tested . In flour disk bioassays, safrole showed very slight Feeding deterrence ag ainst S. zeamais adults, and it had no feeding deterrence against T. castan eum adults and larvae. In contrast, isosafrole was a more effective feeding deterrent than safrole, with feeding deterrence indices of 31% for S. zeam ais adults at 5.4 mg/g of food, and 72 and 40% for T castaneum adults and l arvae, respectively, at 10.8 mg/g of food. It reduced relative growth rate, relative consumption rate, and efficiency of conversion of ingested food o f adults of both species, but only relative growth rate and relative consum ption rate of T. castaneum larvae. Isosafrole was a stronger feeding deterr ent against S, zeamais than against T. castaneum. Both of the compounds sho wed inhibitory effects on a-amylase activity from T. castaneum larvae in vi tro. Safrole also inhibited the larval cr-amylase in vivo. However, isosafr ole inhibited alpha-amylase activity at the lower concentration but activat ed it at the higher concentration in vivo.