Host-Dependent Competitive Dynamics Between Two Trichogramma Parasitoids in Host Eggs

Interspecific competition among parasitoids significantly influences the efficiency and stability of biological control programs; however, competitive interactions occurring inside host eggs remain poorly understood because conventional approaches mainly rely on adult emergence outcomes. This study investigated the temporal dynamics of competition between Trichogramma dendrolimi and Trichogramma ostriniae in two host systems, the eggs of Ostrinia furnacalis, the Asian corn borer, and Corcyra cephalonica, the rice moth, using species-specific molecular detection. Sequential parasitization assays were performed with reversed introduction sequences (T. dendrolimi–T. ostriniae and T. ostriniae–T. dendrolimi), followed by molecular identification of parasitoid persistence at eight developmental time points after parasitization. Three detection states were identified: T. dendrolimi-only, T. ostriniae-only, and simultaneous T. dendrolimi + T. ostriniae detection. Results demonstrated that developmental progression was the strongest determinant of parasitoid detection transitions. Oviposition sequence showed no significant overall effect, although descriptive differences between introduction sequences were observed within individual host species. Early developmental stages were characterized by simultaneous detection of both parasitoids, indicating initial coexistence within host eggs. However, simultaneous detection rapidly declined, followed by host-specific dominance patterns. In O. furnacalis eggs, T. ostriniae became the predominant molecular signal during later development, exceeding 75% detection frequency, whereas T. dendrolimi remained comparatively lower. Conversely, in C. cephalonica eggs, T. dendrolimi showed greater molecular persistence, reaching approximately 60% detection frequency during later developmental stages. Host species significantly influenced molecular detection outcomes, demonstrating host-associated differences in parasitoid molecular persistence. These findings reveal that parasitoid competition is a dynamic developmental process rather than a simple outcome of emergence success and highlight the importance of host-dependent interactions in optimizing Trichogramma-based biological control strategies.