Although Trichogramma principium (Sugonjaev & Sorokina) (Hymenoptera: Trichogrammatidae) is an effective natural enemy in agricultural ecosystems, its tri-trophic interactions should be investigated in more detail. In the present study, life table parameters of the parasitoid wasp and its population projection were investigated under controlled conditions (25 ± 1 °C, 60 ± 5% RH, and 16:8 h L:D) on Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae). The herbivore was reared using three different cultivars, including Early Urbana, Super Strain-B, and Primo Early, as well as being treated with four nitrogen levels (0, 2100, 3000, and 3900 ppm). Data analysis was performed based on an age-stage two-sex life table by linking the life table parameters and population projection. Results indicated a significant increase in net reproductive rate (R0) and intrinsic rate (r). Therefore, the fertilized treatments were relatively favorable hosts for the herbivore and consequently for the parasitoid wasps than unfertilized treatments. Population projection results also indicated differences in the stage population growth rate, age-staged population fluctuations and the parasitism capacity of the parasitoid. These findings indicated that linking life table and population projection is an appropriate method for clarifying the precise timing and the successful release of natural enemies.
