The biology of Canadian weeds. 114. Symphyotrichum pilosum (Willd.) Nesom (Aster pilosus Willd.)

Symphyotrichum pilosum (Willd.) Nesom, the white heath aster, is a robust, native North American, polyploid, herbaceous perennial. Until recently the species was treated as part of Aster. Its placement in the segregate genus Symphyotrichum follows the revised generic combinations proposed for North American asters. Occurring throughout eastern North America from Nova Scotia and Maine in the northeast, southward to Georgia, west ward through southern Quebec and Ontario to Wisconsin, Iowa, Kansas, and Arkansas in disturbed areas such as fallow land, roadsides, dumps, quarries, arable fields, railroad beds, and embankments, the species is troublesome in the United States but a weed of minor importance in Canada. Two varieties, var. pilosum and var. pringlei are recognized. The former, the hairy variety, is weedier than the latter, the hairless variety. The species commonly occurs in fields following the first year of abandonment and may dominate in the second, or subsequent years. Control may be achieved through the application of selected herbicides. Also, even a moderate amount of grazing by herbivores such as small rodents and rabbits is sufficient to restrict growth in the species. Mildew is chronic and widespread in natural populations but typically neither kills the plants nor prevents seed production. This contribution summarizes the known biological data for the species. Key words: Symphyotrichum pilosum, Aster pilosus, white heath aster, weed biology, var. pilosum, var. pringlei

Autumnal Populations of Arthropods on Aster and Goldenrod in the Delta of Mississippi

During the period 30 September to 22 October 1986, 8054 arthropods were captured by sweepnet on flowering Aster pilosus (aster) and Solidaqo altissima (goldenrod). The principal species captured were two Miridae (Heteroptera): the tarnished plant bug (TPB), Lygus lineolaris (22%), and Taylorilygus pallidulus (TPAL) (22 %). Phytophages, most of which were mirids, represented 77 % of the assemblage. TPB was twice as abundant as TPAL on aster; the opposite was true on goldenrod. These two mirid species represented 74 % of the phytophages on goldenrod, but only 44 % on aster. Spiders represented 71 % of the predator/parasite component. Significantly more predators occurred on aster than on goldenrod. The most abundant predator was a spider, Misumenops sp. (Thomisidae). Differences between the compostion of the arthropod communities on aster and goldenrod may be due to differences in plant architecture and its effect on predator success. Very high densities of TPB on autumnal aster and goldenrod may lead to high TPB densities the following spring prior to dispersal onto cotton.

The cytogeography of Aster pilosus var. pilosus in southern Ontario revisited (Compositae: Astereae)

Chromosome numbers were determined for 228 individuals (215 populations) of Aster pilosus var. pilosus from a wider area of southern Ontario than previously reported. Tetraploids occurred throughout the known distribution of the variety in southern Ontario, and the majority were found on clay plains and bedrock outcrops. Hexaploids were by and large restricted in distribution to glacial moraine and till and sand deposits in the "Ontario Island" region, where tetraploids were infrequent, and in parts of the southern Niagara Peninsula, where tetraploids were more common. Two pentaploids were encountered.

RELATIONSHIPS BETWEEN ASTER PILOSUS (COMPOSITAE), MISUMENOPS SPP. (ARANEAE: THOMISIDAE), AND LYGUS LINEOLARIS (HETEROPTERA: MIRIDAE).

Sweep sampling and whole-plant examinations of the Hairy Aster, Aster pilosus (Compositae), were conducted in habitats adjacent to cotton in Mississippi. A strong negative correlation was demonstrated between population densities of the crab spider, Misumenops spp. (Araneae: Thomisidae), and the tarnished plant bug (TPB), Lygus lineolaris (Heteroptera: Miridae). Misumenops spp. populations were highest on large, isolated, bush-like A. pilosus individuals and lowest on small, sparsely branched plants in clusters. When differences in the number of flowers and flower buds between the two growth forms were accounted for, TPB were five times more abundant on small plants. Predation on TPB by Misumenops spp. was observed, and the sampling data suggest that TPB populations are negatively impacted by high population levels of Misumenops spp. Changes in the management of road and field margins and fallow fields are suggested that could increase bush-like A. pilosus densities, leading to larger populations of Misumenops and subsequent smaller populations of TPB.