We tested 10 cm × 10 cm mesh egg-sentinel envelopes (ESEs) containing emerald ash borer eggs on filter paper, and assessed how 2 different mesh sizes (0.5 mm and 1 mm) affected parasitism by Oobius agrili in the laboratory, and parasitism and predation in the field. Mesh size significantly affected parasitism in the laboratory, with the 0.5 mm mesh reducing parasitism by approximately 20% relative to the 1 mm mesh. Parasitism was much lower in the field with no significant difference among treatments, but the 0.5 mm mesh did significantly reduce predation by almost 50% in comparison to the 1 mm mesh. To reduce egg predation while enabling detectable levels of parasitism by O. agrili, we therefore recommend using mesh screen 0.5 mm wide to create ESEs for field deployment.