Lymantria dispar; CONTROL-BY; Cotesia melanoscela (Hymenoptera); HYMENOPTERAN-PARASITES; Cotesia melanoscela; Parasitoid development time & size, genetic variation, control implications Cotesia melanoscela; CONTROL-OF; Lymantria dispar (Lepidoptera); SIZE-; Larvae; LARVAL-DEVELOPMENT; PUPAL-DEVELOPMENT; Duration; VARIATION-; Development time & size, lepidopteran host control implications; LEPIDOPTERAN-HOSTS; Lymantria dispar; Parasitoid development time & size, genetic variation, control implications Little is known about the extent to which traits that can affect the laboratory and field performance of parasitoids as biological control agents are under genetic control. This is particularly true of parasitoids showing potential against the gypsy moth, Lymantria dispar (L.), the most damaging defoliator of deciduous trees in North America. This study examines the effects of genetic variability on the development times and size of the gypsy moth larval parasitoid Cotesia melanoscela (Ratzburg) (Hymenoptera: Braconidae). Heritability indices of size parameters were higher than those for development times. Implications for laboratory rearing and biological control are discussed. none