Warren T. Mays

Evaluation of Aestival Diapause in Hemlock Woolly Adelgid (Homoptera: Adelgidae)

Abstract 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.

Influence of Temperature on Development of Hemlock Woolly Adelgid (Homoptera: Adelgidae) Progrediens

There are three generations of hemlock woolly adelgid, Adelges tsugae Annand, that develop on the secondary host Tsuga spp. Two of these generations, the progrediens and sexupara, are present concu...

DISPERSAL OF TRICHOSIROCALUS HORRIDUS (PANZER) (COLEOPTERA: CURCULIONIDAE) IN SOUTHWEST VIRGINIA

Following the establishment of Trichosirocalus horridus (Panzer) (Coleoptera: Curculionidae), a rosette feeding weevil which was initially released in Southwest Virginia from 1974 to 1977 for the biocontrol of thistle, a study of its dispersal was conducted from 1981 to 1985. Trichosirocalus horridus covered an area of 609 km2 by 1981 and extended its range to 4,345 km2 by 1985. Thirty to 50% of the area was forested and did not support thistles. The remainder of the land consists of small farms with crops, pasture, and small towns, with adequate hosts in most areas. Four thistle species were found infested by T. horridus: Cirsium vulgare (Savi) Tenore (39% of the total plants found), C. discolor (Muhl.) Spreng. (32%), Carduus thoermeri Weinmann (23%), and C. acanthoides L. (6%). Of the thistles examined, 54% of C. thoermeri, 20% of C. acanthoides, 20% of C. vulgare and 6% of C. discolor were infested with T. horridus.