Parasitism performance and developmental adaptability of <i>Trichogramma</i> parasitoids on <i>Helicoverpa armigera</i> (Hübner) eggs of different ages

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is a major pest of key economic crops worldwide. Heavy reliance on chemical control has led to growing issues of insecticide resistance and environmental problems. To explore sustainable alternatives, this study systematically evaluated the parasitism performance and developmental suitability of 5 native Chinese Trichogramma species/strains (Hymenoptera: Trichogrammatidae)-T. dendrolimi Matsumura (with 2 geographical strains from Jilin and Guizhou Province), T. chilonis Ishii, T. ostriniae Pang & Chen, and T. japonicum Ashmead-on H. armigera eggs of different ages (0, 1, and 2 days old). Under selective conditions, T. chilonis, T. japonicum, and T. ostriniae showed a significant preference for 0-day-old eggs of H. armigera. T. dendrolimi (GZ) exhibited no significant preference for egg age, while the JL strain preferred 1-day-old eggs. Under no-selective conditions, all Trichogramma species/strain were able to parasitize host eggs of various ages. The parasitism rates of T. chilonis and T. ostriniae decreased with increasing egg age (39.07% to 34.47% and 45.33% to 39.93%, respectively). The 2 strains of T. dendrolimi performed excellently, with parasitism rates exceeding 60% on eggs of all ages, and even surpassing 70% on 1-day-old and 2-day-old eggs. T. japonicum performed the worst on older host eggs (28.2% to 31.4%). All species exhibited high emergence rates (>90%) and a high proportion of female offspring (≥79%), with T. ostriniae having the highest female ratio. The developmental duration (9.2 to 9.9 days) was similar across species. In summary, 2 geographical strains T. dendrolimi stands out as the most promising and dominant candidate for biological control of H. armigera.