Journal of Chemical Ecology

, Volume 29, Issue 2, pp 303-320

First online:

Herbivore-Induced Responses in Alfalfa (Medicago sativa)

  • Jep AgrellAffiliated withDepartment of Animal Ecology, Lund University Email author 
  • , Wieslaw OleszekAffiliated withDepartment of Biochemistry, Institute of Soil Science and Plant Cultivation
  • , Anna StochmalAffiliated withDepartment of Biochemistry, Institute of Soil Science and Plant Cultivation
  • , Maria OlsenAffiliated withDepartment of Animal Ecology, Lund University
  • , Peter AndersonAffiliated withDepartment of Crop Science, Swedish University of Agricultural Sciences

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The herbivore-induced response of alfalfa (Medicago sativa) was examined through assays with Spodoptera littoralislarvae and analyses of important secondary substances. In food preference experiments, larvae preferred young undamaged alfalfa plants over plants that had been damaged by feeding larvae 5 and 7 days earlier, while no difference in feeding preferences could be detected 1, 9, and 14 days after damage. This suggests a peak in the herbivore induced resistance of alfalfa approximately one week after initial damage. The induced resistance in young plants was also shown to be systemic, while older flowering plants failed to show increased resistance after defoliation. Larvae gained weight slower and had lower pupal mass when fed damaged alfalfa than when fed undamaged alfalfa. Levels of total saponins were increased in foliage of damaged alfalfa, and detailed analyses of specific saponin components revealed doubled concentrations of 3GlcA,28AraRhaXyl medicagenate (medicagenic acid bidesmoside) and 3GlcAGalRha soyasapogenol B (soyasaponin I). Levels of the flavonoid apigenin (as free aglycone) also were increased in herbivore damaged plants. The herbivore-induced response of alfalfa was significantly weaker than that of cotton: S. littoralis larvae given a choice of undamaged cotton and undamaged alfalfa preferred to feed on cotton, whereas preferences shifted towards alfalfa when plants were damaged.

Medicago sativa induced resistance herbivore damage bioassays Spodoptera littoralis phenology phytochemistry defense compounds saponins flavonoids