Simple SummaryThe mass rearing of parasitoids is a basic prerequisite for their use in biological control. If parasitoid rearing is effective, host/parasitoid mixtures will not form. In this study, we used an irradiatedDrosophila melanogasterhost to supply parasitoids and assessed whether all adults that emerged after parasitization wereTrichopria drosophilae. The results of this study showed that irradiation of host pupae for 6 h is the preferred treatment for promoting the emergence and therefore the potential application ofT. drosophilaein the control ofDrosophilapests. At the same time, the results also serve as an important reference for reducing costs and improving the efficiency of biological pest control.AbstractThe pupal parasitoid,Trichopria drosophilaePerkins (Hymenoptera: Diapriidae), is an ectoparasitoid of the genusDrosophilawith great potential for application in biological control based on its excellent control efficiency forDrosophila suzukiiMatsumura (Diptera: Drosophilidae), and it has has even been commercialized by biofactories. Due to its characteristics of short life cycle, large number of offspring, easy rearing, rapid reproduction, and low cost,Drosophila melanogaster(Diptera: Drosophilidae) is currently being utilized as a host to mass produceT. drosophilae. To simplify the mass rearing process and omit the separation of hosts and parasitoids, ultraviolet-B (UVB) was used as an irradiation source to irradiateD. melanogasterpupae, and the effects onT. drosophilaewere studied. The results showed that UVB radiation significantly reduces host emergence and affects the duration of parasitoid development (female: F0 increased from 21.50 to 25.80, F1 from 23.10 to 26.10; male: F0 decreased from 17.00 to 14.10, F1 from 17.20 to 14.70), which has great significance for the separation of hosts and parasitoids as well as of females and males. Of the various studied conditions, UVB irradiation was ideal when the host was supplied with parasitoids for 6 h. The selection test results showed that the female-to-male ratio of emerging parasitoids in this treatment was highest at 3.47. The no-selection test resulted in the highest rates of parasitization and parasitoid emergence rate, maximized inhibition of host development, and allowed the omission of the separation step. Finally, the results of the semi-field test showed that the parasitoids bred in this treatment could search for their hosts normally and could therefore be directly applied in the biological control ofDrosophilapests in the field.