, Volume 26, Issue 4, pp 1065-1078

Effects of Alfalfa Saponins on the Moth Spodoptera littoralis

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Alfalfa saponins administered to Spodoptera littoralis in the larval diet caused prolongation of the larval and pupal stages, retarded growth, increased mortality, and reduced fecundity and fertility. At least some of these effects were probably due to digestion problems manifested by longer food retention in the gut. Preliminary data indicated that the efficiency of food utilization was not altered. Saponin aglycones exerted similar developmental derangements; medicagenic acid proved most active; hederagenin, soysaponogenol A, and soysaponogenol B exhibited moderate activities; and soysaponogenol E was inactive. It is proposed that saponins become active only when the sugar component is cleaved off by the gut glycosylases and that substrate specificity of these enzymes is decisive for the activity of ingested saponins. For example, all tested α-L-arabinopyranosyl glycosides were inactive, while the corresponding aglycones or glucosides were active. The liberated aglycones are apparently deposited in the tissues and exert post-feeding disturbances such as delay of imaginal ecdysis and reduced egg hatchability.