Antifeedant activities of terpenoids isolated from tropical Rutales

Terpenes isolated from tropical species of the Rutales were tested for insect antifeedant activity against rice weevil, Sitophilus oryzae (L.) using a flour disk bioassay that requires only small amounts of compounds (0, 0.05, 0.25 and 0.50% w/w). At 0.50% (w/w) five compounds isolated from Lansium domesticum (iso-onoceratriene, 3-keto-22-hydroxyonoceradiene, onoceradienedione, lansiolic acid and lansiolic acid A) were shown to exhibit significant antifeedant activity. Humilinolide C and D isolated from Swietenia humilis, and gedunin from Cedrela odorata, were also active at 0.50% (w/w). The most interesting results were obtained from the spirocaracolitones from Ruptiliocarpon caracolito which produced total feeding inhibition at 0.50% and potent antifeedant activity at concentrations as low as 0.05%. In conclusion, the antifeedant bioassay provides a rapid and inexpensive method for screening novel compounds available in small quantities to assess their activity as insect antifeedants.