For parasitoid wasps, nutrition is crucial to ensuring their survival and reproductive success. Nevertheless, the accessibility of nutritional sources, particularly plant nectar, may fluctuate significantly within agricultural environments. This variability may impact the fitness of parasitoids and consequently their effectiveness in pest control. The egg parasitoid Gryon aetherium Talamas (Hymenoptera, Scelionidae) is a promising candidate as a biological control agent against the painted bug Bagrada hilaris (Burmeister) (Hemiptera, Pentatomidae), a pest that was not recorded in Chile (South America) until 2016. Consequently, its recent invasion has renewed the interest in its biological control, especially in conservation biological control (CBC), as an effective and sustainable approach to managing this pest. Since the effectiveness of G. aetherium depends on its survival and conservation within agroecosystems, the provision of flowers as food resources (nectar) constitutes a sugar-rich food source to increase its fitness. In Chile, Coriandrum sativum L., Petroselinum crispum (Mill.), Foeniculum vulgare Mill. (Apiaceae), Lobularia maritima (L.) (Brassicaceae) and Pelargonium hortorum Bailey (Geraniaceae) were effectively tested in the field to attract and support the natural enemies of different cabbage pests. In this study, we evaluated the potential of these selected flowers to enhance the performance of the parasitoid G. aetherium under laboratory conditions using water as the control. Our results demonstrate that G. aetherium exhibited increased survival when provided with C. sativum and P. crispum flowers compared to F. vulgare, L. maritima, P. hortorum and water, respectively. Moreover, the fecundity and emergence rates were similar across all of the flower treatments but were significantly reduced when exposed to water. Furthermore, a female-biased sex ratio was observed in the flower treatments. This information may be applied to enhancing the floral diversity in agroecosystems through “ecological engineering”, ultimately improving the effectiveness of conservation biological control.