The effects of long-term mass rearing of laboratory insects on ecologically relevant traits is an important consideration when applying research conclusions to wild populations or developing management strategies. Laboratory strains of the gypsy moth, Lymantria dispar (L.), an invasive forest pest in North America, have been continuously reared since 1967. Selection on these strains has enhanced a variety of traits, resulting in faster development, shorter diapause, and greater fecundity. As in many mass-reared insects, laboratory strains of the gypsy moth are also reared exclusively on artificial diets that lack much of the phytochemical and nutritional complexity associated with natural foliage.We tested for differences in growth and development of wild gypsy moth populations from across the invasive range in comparison to laboratory strains when reared on artificial diet and a preferred foliage host species, northern red oak (Quercus rubra L.). Overall, caterpillars reared on foliage had higher survival and faster development rates, with smaller differences among populations. When reared on artificial diet, laboratory strains had the highest performance as expected. The response from the wild populations was mixed, with two populations performing poorly on artificial diet and another performing nearly as well as the laboratory strains. Performance on diet was enhanced when larvae received cubed portions changed regularly, as opposed to filled cups. Understanding these relationships between food source and population performance is important for informing studies that examine population comparisons using wild and laboratory- reared strains.