Antifeedant and growth inhibitory effects of extracts and drimanes of Drimys winteri stem bark against Spodoptera littoralis (Lep., Noctuidae)

Antifeedant and toxic activity of crude plant extracts [n-hexane, acetone, methanol:water (80:20)], and the drimanes (drimendiol, isodrimeninol, isotadeonal and polygodial) isolated from the stem bark of Drimys winteri J.R. Forster et G. Forster (Winteraceae) were investigated in the Egyptian cotton leafworm, Spodoptera littoralis (Boisduval) (Lep., Noctuidae) using different bioassays. n-Hexane extract at 5000 ppm and the drimane polygodial at 1000 ppm exhibited the strongest antifeedant activity against sixth instar larvae when applied on leaf discs under choice and no-choice conditions (feeding deterrence index: 75.5% and 94.7% for n-hexane and polygodial, respectively, on the choice test). Nutritional indices were calculated after exposure of L6 to the drimanes over a 12 h period, resulting in reduced feeding and growth rates, being significantly higher with polygodial. To distinguish between antifeedant and toxic effect, growth efficiency, calculated from the values of relative consumption and relative growth rates after exposure to non-treated leaf discs for 12 h more to the same larvae which had been exposed on the previous bioassay. From the results, it is concluded that only polygodial and isodrimeninol exert their toxic effects at physiological level. Polygodial was the most potent feeding and growth inhibitor for S. littoralis (DC50 = 708 ppm and EC50 = 198 ppm, respectively).