Electrical Penetration Graph analysis reveals population differentiation of host-plant probing behaviors within the aphid species Uroleucon ambrosiae

Uroleucon ambrosiae collected from the eastern and the southwestern United States were studied in relation to host-plant probing. In the field, easter n aphids are highly specific on Ambrosia trifida, while southwestern aphids feed on Ambrosia trifida plus many other species in the family Asteraceae. Electrical penetration graphs of insects on the principal host, A. trifida , and an additional host of southwestern populations, Heterotheca subaxilla ris, revealed regional differentiation in host-associated aphid behaviors, specifically in the first phase of subcuticular probing, and in phloem find ing activities. Eastern aphids used A. trifida more efficiently than southw estern aphids, but were demonstrably less vigorous in their probing activit ies on H. subaxillaris.