Three hundred eighty-two freshly oviposited gypsy moth, Lymantria dispar (L.), egg masses from two laboratory strains (fertile and F₁-sterile) and one wild strain were subjected to seven temperature regimes. Egg hatch was monitored daily in each egg mass until egg hatch was completed. The hatch pattern of each strain in each temperature regime was described by a cumulative distribution of percentage of total egg hatch, and distributions were compared statistically. Egg hatch distributions differed significantly in all but three of the 21 comparisons. However, cumulative egg hatch milestones of 5, 50, and 95% were reached by the F₁-sterile egg masses <1, 2, and 4 d later, respectively, than either the laboratory fertile or wild strains. These differences are small relative to the ≈8 mo spent in the egg stage, and they should not invalidate the use of F₁-sterile egg masses as sentinel eggs where the risk of establishment with fertile eggs is deemed too great.