Studies of certain parameters affecting two parasitoid species, Trichogramma evanescens Westwood and Trichogrammatoidea bactrae Nagaraja (Hymenoptera: Trichogrammatidae), on egg host, Sitotroga cerealella (Olivier) (Gelechiidae: Lepidoptera)

Abstract Background Two Trichogramma spp., Trichogramma evanescens Westwood and Trichogrammatoidea bactrae Nagaraja (Hymenoptera: Trichogrammatidae), were studied to control one of the most cereal pests attacking various grains, Sitotroga cerealella (Olivier) (Gelechiidae: Lepidoptera). Experiments were carried out to evaluate S. cerealella egg-ages, parasitoids’ emergence time and cold storage host eggs on rearing the two tested parasitoids’ spp. Results The age of S. cerealella eggs had significantly influenced the parasitization and adult emergence rates of the two parasitoid species. Parasitism rate resulted from old host eggs (32 h old) (44.93%) decreased than those of the fresh ones (2 h old) (95.85%). Emergence rate ranged between (62.64–97.85%) for T. evanescens and (62.90–95.54%) for T. bactrae from different S. cerealella egg-ages (0–32 h). Regardless to late emerged parasitoids, their population affected. T. evanescens parasitized rate ranged (73.79–95.06%), which comparatively lower than those of T. bactrae (88.81–96.90%), at parasitoid emerging times (0–64 h), respectively. Emergence times had significantly differences in the emergence rate of T. evanescens and/or T. bactrae. On the other hand, percentage of parasitism of the non-stored S. cerealella eggs was higher than the other cold-stored ones. The emergence rate of adult parasitoids, T. evanescens (66.00–91.16%) and T. bactrae (71.16–94.11%), was decreased at the cold storage durations (5–40 days) increased. In comparison  to the tested biological aspects between the two parasitoid species, non-significant differences were recorded, at the three assessment parameters, which include host egg-ages, parasitoid emergence time and cold-stored eggs. Meanwhile, there were significant differences between F1 emerged rates for T. evanescens and T. bactrae obtained at each of the three tested parameters. Conclusion It was concluded that low emergence time of the parasitoids, T. evanescens and T. bactrae, was relatively more effective when they parasitized the fresh egg-age and less cold storage periods of S. cerealella.