‘Canby’ red raspberry is immune and ‘Latham’ is susceptible to infestation byAmphorophora agathonicaHottes. During a 4-day period, nymphs gained more dry weight and nitrogen on Latham than on Canby. On Latham the dry weight and nitrogen content of honeydew were greater and lO× more total solids and 2× more total nitrogen were ingested than on Canby. Using the volume of honeydew produced per aphid as an index of the quantity of sap ingested, equal or greater volumes of sap were ingested on Canby than Latham. The ingestate from Canby was more dilute than that from Latham.The phloem tissue in petioles of intact Canby leaves was destroyed, but the xylem left intact, by stem girdling. Nymphs on girdled Canby leaves gained as much dry weight as those on normal Latham leaves. Those on the girdled leaves ingested more total solids and more total nitrogen than those on the normal Canby leaves. When girdled Canby leaves were shaded from light, and photosynthesis prevented, nymphs ingested more total nitrogen than those on normal Canby leaves. The levels of total solids ingested from the girdled and shaded and the normal leaves did not differ. On the girdled and shaded Canby leaves the gain in dry weight by the nymphs was intermediate between that on girdled leaves of Canby and normal leaves of Latham, and that on normal leaves of Canby.These results suggest that the immunity of Canby is related to the levels of both solids (largely sugars) and nitrogenous compounds in the ingestate ofA. agathonica. It is not known whether this relationship is quantitative and/or qualitative in nature.