Effects of alfalfa saponins on the moth Spodoptera littoralis

Alfalfa saponins administered to Spodoptera littoralis in the larval diet c aused prolongation of the larval and pupal stages, retarded growth, increas ed mortality, and reduced fecundity and fertility. At least some of these e ffects were probably due to digestion problems manifested by longer food re tention in the gut. Preliminary data indicated that the efficiency of food utilization was not altered. Saponin aglycones exerted similar developmenta l derangements; medicagenic acid proved most active; hederagenin, soysapono genol A, and soysaponogenol B exhibited moderate activities; and soysaponog enol E was inactive. It is proposed that saponins become active only when t he sugar component is cleaved off by the gut glycosylases and that substrat e specificity of these enzymes is decisive for the activity of ingested sap onins. For example, all tested alpha-L-arabinopyranosyl glycosides were ina ctive, while the corresponding aglycones or glucosides were active. The lib erated aglycones are apparently deposited in the tissues and exert post-fee ding disturbances such as delay of imaginal ecdysis and reduced egg hatchab ility.