Date of this Version
The water-soluble fraction of Melilotus leaves previously referred to as Stimulant A was further fractionated by preparative paper chromatography into three factors, each having a stimulatory effect on sweetclover weevil feeding. The three factors, designated Stimulant A1, A2, and A3, were identified as sucrose, glucose, and fructose, respectively, by co-chromatography with known sugars on cellulose-coated thin-layer plates. Silver nitrate, anisidine phthalate, and anthrone were employed as detection agents. The isolated compounds and corresponding reagent grade sugars were identical in chromatographic and chemical behavior, as well as in feeding stimulant activity. Sucrose stimulated the greatest amount of feeding when the three sugars were compared at equal concentration in the same bioassay. Disks treated with glucose and fructose were fed upon equally at the three concentrations tested. Although these sugars probably playa significant role in the mechanism of resistance and susceptibility of Melilotus plants to weevil feeding, it is not likely that they are wholly responsible for the host specificity displayed by the sweetclover weevil.