INSECT FLOWER VISITATION FREQUENCY AND SEED PRODUCTION IN RELATION TOPATCH SIZE OF VISCARIA-VULGARIS (CARYOPHYLLACEAE)

We examined frequency of pollinator visits, seed set, and seed predati on in relation to plant patch size of the perennial caryophyllaceous h erb Viscaria vulgaris in two areas in southern Sweden. The Dalsland ar ea had approximately ten times more Viscaria plants per unit area than the Smaland area. Long-tongued bumblebees and to a lesser extent Lepi doptera were the most important pollinators in both areas. Honeybees a nd bumblebees with short proboscides were mainly nectar robbers and/or pollen collectors. Insect visitation per Viscaria plant and patch siz e were either unrelated or negatively correlated. However, bumblebee v isitation was twice as high in the Dalsland area compared to Smaland, while no such difference was found in Lepidoptera. Despite similar vis itation rates and similar potentials for seed set, natural seed set in creased with patch size. Thus, a pollinator may, on average, deposit m ore Viscaria pollen per flower visit in large patches than in small pa tches. Fruit set, i.e. the proportion of flowers setting fruits, was h igher during wet years than during dry years and differed with plant s ize in four out of five years, suggesting resource limitation. Fruit s et therefore is not a reliable measurement of pollination effectivenes s in this species. Seed-feeding insect larvae were more abundant in la rge patches and consumed more than 60% of seed capsules in the largest patches. We conclude that Viscaria plants in large patches produce mo re seeds but also suffer increased risk of being attacked by seed-eati ng insects or infected by disease.