Evaluation of aestival diapause in hemlock woolly adelgid (Homoptera : Adelgidae)

Two hemlock woolly adelgid, Adelges tsugae Annand, generations complete the ir development on hemlocks (Tsuga spp.) that are native to eastern North Am erica. Progrediens are present in the spring and sistens are present from e arly summer until the following spring. Following the settling of sistens c rawlers at the base of hemlock needles, first-instar sistens go into aestiv al diapause for approximate to4 mo. We conducted studies to determine if we could prevent the induction of diapause and determine the environmental co nditions required to do so. Diapause was determined to be maternally regula ted. We were able to prevent the induction of diapause by preconditioning p arents at 12 and 14.5 degreesC, but not at 17 degreesC, indicating that tem perature is a critical preconditioning cue. Preventing the induction of dia pause 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 sta ge through second-instar progrediens were found to be the maternal lifestag es sensitive to diapause-inducing cues.