This dataset contains experimental data from a laboratory study assessing the impact of host egg age on the biological performance of Trichogramma galloi Zucchi, 1988 (Hymenoptera: Trichogrammatidae), an important egg parasitoid of the sugarcane borer Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae). The data comprise raw counts and derived metrics for five host egg ages (1 to 5 days old), including: Parasitism rate: number of host eggs parasitized. Viability: proportion of parasitized eggs from which adult parasitoids successfully emerged. Clutch size per egg: number of immature parasitoids developing per egg. Development time: duration (in days) from oviposition to adult emergence. Sex ratio: proportion of female offspring. Adult longevity: lifespan of emerged parasitoids by sex (female/male). The study also includes histological observations and statistical analyses using one-way ANOVA, Tukey’s HSD, and generalized linear models (GLMs). These data were used to evaluate stage-specific host suitability and inform strategies for timing mass-releases in biological control programs targeting D. saccharalis in sugarcane systems. All data were recorded under controlled laboratory conditions and are organized into individual Excel sheets per metric, as well as a unified CSV version for reproducibility and reanalysis.