The effects of the defensive chemistry ofSolidago altissimaon the cabbage looper,Trichoplusia ni(Hübner), were shown using artificial diet bioassays. LyophilizedS. altissimaleaves were incorporated into an artificial diet. Leaf powder also was extracted in hexane, methanol, and water, and the extracts and postextraction residue were incorporated separately into artificial diets. The control contained cellulose powder in place of leaf material. Also, larvae were grown on live, intactS. altissimaplants. The mortality rate was 100% in the whole-leaf powder and methanol extract diets, 97.2% in the hexane extract diet, and 96% in the live-plant experiment. Mortality on the water extract diet (12%) and on the residue-containing diet (13%) was lower than that on the cellulose powder control (17.4%).S. altissimacontains chemicals that severely reduce larval survivorship ofT. ni, but once these chemicals are removed through extraction, the larvae are able to use the nutrients contained in the leaves. These nutrients increase survivorship to adulthood above that on the cellulose control hut do not significantly affect time to pupation, pupal mass, or fecundity.