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

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Abstract
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.