A New Virulent Biotype of the Spotted Alfalfa Aphid in Arizona12

A new virulent biotype of Therioaphis maculata (Buckton) was collected from populations infesting ‘Mesa-Sirsa’ alfalfa at Mesa and Poston, AZ. The new strain, designated H, and biotype F, reproduced and survived on 6 of 9 parent clones of ‘Moapa’ alfalfa. Clone C-907 was susceptible to H and resistant to F, clearly separating the 2 closely related biotypes. Both biotypes were identically susceptible to 4 organophosphate insecticides.