The absence of natural enemies in newly invaded areas is a key factor in the successful invasion of alien species. Whether a specific parasitoid can be domesticated to attack a nonnatural host that has no reported parasitic enemies in invasive areas remains unclear. Here, we analyzed two invasive mealybugs (PSS-Phenacoccus solenopsis and PSI-Phenacoccus solani) and a specific parasitoid of P. solenopsis (Aenasius arizonensis) to verify this hypothesis under laboratory conditions. A. arizonensis preferred to parasitize PSS, but after 6 h, it also parasitized PSI female adults. The number of visits and parasitism rate was significantly higher for PSS than for PSI. However, the contact time was influenced by the natal host. The chemical volatiles emitted by the two hosts were different and may be an important factor for host choice. Offspring fitness, measured as emergence time, longevity, and hind tibia length, in those emerging from PSS was better in those emerging from PSI, but the emergence rate was higher in the latter. We supposed that A. arizonensis accepts and parasitizes low-quality hosts not because of an "incomplete" evaluation but because it may be more profitable to parasitize than not given circumstances; this may provide an opportunity for the control of a new invasive mealybug in the future.