Evaluation of large raspberry aphid (Amphorophora agathonica) feeding behavior on susceptible and resistant red raspberry

The large raspberry aphid Amphorophora agathonica Hottes is an important virus vector in red and black raspberries in North America. Host plant resistance in the form of a single dominant gene named Ag1 has been relied upon to help control virus diseases, however, the mechanism of resistance is poorly understood. Aphid feeding was monitored using the electrical penetration graph (EPG) on a resistant red raspberry cultivar, ‘Tulameen’, and compared to a susceptible control, ‘ORUS 2786-5’. There were no differences in pathway feeding behaviors performed by aphids as they moved toward the phloem. Once in the phloem, aphids feeding on resistant plants spent significantly more time salivating than on susceptible plants, and significantly less time ingesting phloem sap. This suggests a mechanism for resistance to A. agathonica is located in the phloem.