Parasitoid wasps released as biological control agents may experience strong interspecific competition, which can lead to a reduction in pest control. The effects of competition can be mitigated if niche partitioning exists between species, such as parasitism preferences for different host stages. We examined host stage preferences for the parasitoids Encarsia noyesi Hayat (Hymenoptera: Aphelinidae), Idioporus affinis LaSalle and Polaszek (Hymenoptera: Pteromalidae), and Entedononecremnus krauteri Zolnerowich and Rose (Hymenoptera: Eulophidae). These parasitoids were introduced to the United States to control the giant whitefly Aleurodicus dugesii Cockerell (Hemiptera: Aleyrodidae), a pest of many economically important plants. Host stage preferences were examined using multiple metrics including: parasitism rates, relative preferences, handling times, and initial stage parasitism frequency. The data indicated differences in parasitoid preference hierarchies for the four A. dugesii nymphal stages. All A. dugesii nymphal stages were parasitized by I. affinis, which exhibited preference for the third instar. Unlike I. affinis, the first instar was not parasitized by E. noyesi, and its preference hierarchy differed with the fourth instar being the most preferred stage. The observed host-use breadth of E. krauteri was the narrowest observed of the three parasitoid species, only parasitizing the fourth and third instars, with a clear preference for the former. The observed differences in host-use breadth and stage preferences between parasitoid species in this system may promote their long-term coexistence in the field and facilitate biological control. Potential factors underlying the preferences exhibited by these parasitoids and their implications for biological control are discussed.