The aphid Amphorophora agathonica Hottes (Hemiptera: Aphididae) is an important virus vector in red (Rubus idaeus L.) and black (Rubus occidentalis L.) raspberries in North America. Raspberry resistance to A. agathonica in the form of a single dominant gene named Ag 1 has been relied upon to help control aphid-transmitted plant viruses; however, the mechanism of resistance to the insect is poorly understood. Aphid feeding was monitored using an electrical penetration graph on the resistant red

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... aspberry ÔTulameenÕ and compared with a susceptible control, ÔVintageÕ. There were no differences in pathway feeding behaviors of aphids as they moved toward the phloem. Once in the phloem, however, aphids feeding on resistant plants spent signiÞcantly more time salivating than on susceptible plants, and ingested signiÞcantly less phloem sap. This suggests that a mechanism for resistance to A. agathonica is located in the phloem. Reduced ingestion of phloem may result in inefÞcient acquisition of viruses and is a likely explanation for the lack of aphid-transmitted viruses in plantings of resistant cultivars.