Journal of Chemical Ecology, Vol. 25, No. 2, 1999 EFFECT OF Solanum GLYCOSIDES ON THE APHID Schizaphis graminum SILVIA SOULE, 1 CARLOS GUNTNER,1 ALVARO VAZQUEZ,1 VICTOR H. ARGANDONA,2 FERNANDO FERREIRA,1,* and PATRICK MOYNA1 1 Catedra de Farmacognosia y Productos Naturales Facultad de Quimica CC1157, Montevideo, Uruguay 2Facultad de Ciencias, Universidad de Chile Casilla 653, Santiago, Chile (Received January 13, 1998; accepted September 24, 1998) Abstract—Common Solanum glycosides were tested against a non-Solanum pest, the greenbug, Schizaphis graminum, fed by artificial diet supplemented with the tested compounds. In contrast with the potato aphid Macrosiphum euphorbiae, S. graminum is sensitive to both potato and tomato glycoalkaloids, as well as to all the different Solanum steroidal glycosides tested. S. graminum was less sensitive to glycoalkaloids than to the steroidal glycosides. Laxumin A (LC50 4.3 MM) and laxumin B (LC50 6.1 MM), isolated from Solanum laxum, were the most active of the tested compounds. The different sensitivity of both aphids against Solanum glycosides could be related to a possible adaptation of the insects to their host plants secondary metabolites. INTRODUCTION Plant secondary metabolites can act as protective agents in plants against insects either by repellence or by direct toxicity (Montllor, 1991; Janzen et al., 1977). Many different types of secondary metabolites including alkaloids, terpenes, steroids, iridoid glycosides, aliphatic molecules, phenolics, and others, have been demonstrated to confer resistance to different plant species against pathogens. Among them, steroidal glycosides and glycoalkaloids are well-known resistance Key Words—Schizaphis graminum, Aphididae, aphids, greenbug, survival, glycosides, glycoalkaloids. *To whom correspondence should be addressed. 369 0098-0331/99/0200-0369/$16.00/0 c 1999 Plenum Publishing Corporation