Two hemlock woolly adelgid, Adelges tsugae Annand, generations complete their development on hemlocks (Tsuga spp.) that are native to eastern North America. Progrediens are present in the spring and sistens are present from early summer until the following spring. Following the settling of sistens crawlers at the base of hemlock needles, first-instar sistens go into aestival diapause for ≈4 mo. We conducted studies to determine if we could prevent the induction of diapause and determine the environmental conditions required to do so. Diapause was determined to be maternally regulated. We were able to prevent the induction of diapause by preconditioning parents at 12 and 14.5°C, but not at 17°C, indicating that temperature is a critical preconditioning cue. Preventing the induction of diapause was also most successful under a photoperiod of 12:12 (L:D) h and was therefore chosen as a standard for rearing hemlock woolly adelgid. Egg stage through second-instar progrediens were found to be the maternal lifestages sensitive to diapause-inducing cues.