Feeding deterrence and contact toxicity of Stemona alkaloids-a source of potent natural insecticides.
On the basis of chronic feeding bioassays with neonate larvae of Spodoptera littoralis reared on an artificial diet, the methanolic leaf and root extracts from Stemona collinsae displayed very high insect toxicity compared to those of two Aglaia species, a commercial Pyrethrum extract, and azadirachtin, whereas S. tuberosa extracts demonstrated low activity in roots and no activity in leaves. Beyond that, in leaf disk choice tests against fifth instar larvae, S. collinsae showed strong antifeedant activity, whereas S. tuberosa was characterized by remarkable repellency. The anti-insect properties of both species were based on pyrrolo[1,2-a]azepine alkaloids, from which didehydrostemofoline (asparagamine A) was the major compound of the roots of S. collinsae, exhibiting the highest toxicity in feeding assays. Saturation and hydroxylation of the side chain in the co-occurring stemofoline and 2'-hydroxystemofoline, respectively, led to an increasing loss of activity. Contact toxicity tests with stemofoline and didehydrostemofoline exhibited even higher activities than those of Pyrethrum extract. Tuberostemonine was the dominating alkaloid in the roots of S. tuberosa, showing outstanding repellency but no toxic effects.
Brem
Brigitte
B
Comparative and Ecological Phytochemistry Department, Institute of Botany, University of Vienna, Rennweg 14, A-1030 Wien, Austria.
Seger
Christoph
C
Pacher
Thomas
T
Hofer
Otmar
O
Vajrodaya
Srunya
S
Greger
Harald
H
D031602:Aglaia / Q000737:chemistry; D000470:Alkaloids / Q000494:pharmacology*; D000818:Animals; D005247:Feeding Behavior / Q000187:drug effects; D006576:Heterocyclic Compounds, 4 or More Rings / Q000494:pharmacology; D007300:Insect Control / Q000379:methods*; D007306:Insecticides / Q000494:pharmacology*; D007814:Larva; D019684:Magnoliopsida / Q000737:chemistry*; D010936:Plant Extracts / Q000494:pharmacology / Q000633:toxicity*; D018515:Plant Leaves; D018517:Plant Roots; D018411:Spodoptera / Q000187:drug effects* / Q000254:growth & development
D000470:Alkaloids; D006576:Heterocyclic Compounds, 4 or More Rings; D007306:Insecticides; D010936:Plant Extracts; C430220:stemofoline