Aphis fabae Scopoli consists of a complex of closely related host plant-associated forms. This system offers insights into speciation and the determinants of plant use in an important insect pest, but concerted study of the complex requires identification of clones with different plant preference that can potentially exchange genes. This study presents a series of hybridizations between clones collected from subspecies-specific host plants Vicia faba (L.), Tropaeolum majus (L.), and Cirsium arvense (L. Scopoli) that are carried out exclusively in the laboratory (mating and diapause) and also in the laboratory with overwintering in the field. Crosses between a V. faba-affiliated clone and T. majus and C. arvense-affiliated clones are not viable, but the cross between the T. majus and C. arvense-derived clones is highly viable and similar in fertility to the cross between the V. faba-derived clones with the same plant species preference (the “control”). It is also found that the female × male; cross between the T. majus and C. arvense-affiliated clones is viable when conducted exclusively in the laboratory but infertile in the laboratory/field crosses. This indicates that modifications of protocol can profoundly affect the outcome of aphid crossing studies and could explain the discrepancies between results of hybridization studies of the A. fabae complex carried out by various workers over the past 50 yr.