title: Triterpene saponins of Quillaja saponaria show strong aphicidal and deterrent activity against the pea aphid Acyrthosiphon pisum.
abstract: BACKGROUND
  Saponins are a class of secondary plant metabolites consisting of a sugar moiety glycosidically linked to a hydrophobic aglycone (sapogenin) that often possess insecticidal activities. Four saponins were selected: two triterpene saponins, Q. saponaria saponins and aescin, and two steroidal saponins, digitonin and diosgenin. Their effects were investigated on an important pest species and a model piercing-sucking insect, the pea aphid Acyrthosiphon pisum. The triterpene Q. saponaria saponins bark saponin received special attention because of its high activity. Aphids were challenged by oral and contact exposure to demonstrate aphicidal activities, and in choice experiments to support use as a natural deterrent.
  
  
  RESULTS
  When aphids were exposed to supplemented artificial diet for 3 days, a strong aphicidal activity was recorded for three of the four saponins, with an LC50 of 0.55 mg mL(-1) for Q. saponaria saponins, 0.62 mg mL(-1) for aescin and 0.45 mg mL(-1) for digitonin. The LT50 values ranged between 1 and 4 days, depending on the dose. For diosgenin, only low toxicity (14%) was scored for concentrations up to 5 mg mL(-1). In choice experiments with treated diet, a deterrence index of 0.97 was scored for Q. saponaria saponins at 1 mg mL(-1). In contrast, direct contact showed no repellent effect. Spraying of faba bean plants with Q. saponaria saponins resulted in an LC50 of 8.2 mg mL(-1). Finally, histological analysis in aphids fed with Q. saponaria saponins demonstrated strong aberrations of the aphid gut epithelium, and exposure of midgut CF-203 cell lines to Q. saponaria saponins in vitro confirmed the cytotoxic effect.
  
  
  CONCLUSIONS
  The present insect experiments provide strong evidence that saponins, as tested here with triterpene Q. saponaria saponins, can be useful as natural aphicides and deterrents. Furthermore, the insect midgut epithelium is suggested to be a primary target of saponin activity.
authors: Department of Crop Protection, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium.
authors: Ellen
authors: E
authors: De Geyter
authors: Guy
authors: G
authors: Smagghe
authors: Yvan
authors: Y
authors: Rahbé
authors: Danny
authors: D
authors: Geelen
mesh_terms: D000818:Animals; D001042:Aphids; D004072:Digitonin; D004144:Diosgenin; D004928:Escin; D007300:Insect Control; D007302:Insect Repellents / Q000032:analysis* / Q000633:toxicity; D007306:Insecticides / Q000032:analysis* / Q000633:toxicity; D007413:Intestinal Mucosa / Q000187:drug effects; D024301:Plant Bark / Q000737:chemistry; D031990:Quillaja / Q000737:chemistry*; D012503:Saponins / Q000633:toxicity; D018675:Toxicity Tests; D031307:Vicia faba / Q000469:parasitology
chemical_list: D007302:Insect Repellents; D007306:Insecticides; D012503:Saponins; D004928:Escin; D004144:Diosgenin; D004072:Digitonin