| Virginia bluebells, Mertensia virginica (L.) Pers., is an herbaceous perennial which grows along streams and moist hillsides within the deciduous forests of the Northeastern United States. M. virginica is one of the first spring wildflowers to come into bloom and is visited by a variety of insect species. Life history data were compiled for M. virginica growing in the Horner Wildlife Sanctuary located in Oldham County, Kentucky USA during the years 1995-1997. The reproductive biology was studied in 1995 with 12 different plants and 6 different pollination treatments. Resource and pollen limitation of seed set were assessed in 1996 using various manipulations to 10 triplets of plants in 10 different locations. In 1995 and 1996, five different patch sizes (1, 5, 10, 20, and 60 plants) were observed and studied in relation to pollinator attractiveness and seed set. In 1997, the effect on seed set of nectar robbery by the bee Bombus affinis in these five different patches was determined.; M. virginica blooms for approximately four weeks during the month of April and produces a maximum of four nutlets per flower by the end of May. M. virginica was found to be self-compatible, but insect visitation is necessary for seed set and cross-pollinations will produce substantially more seeds than self-pollinations. Resource limitation experiments revealed M. virginica to not be nutrient limited within the growing season. The cause of less than maximal seed set per flower is believed to be due to insufficient amounts of pollen being transferred to stigmas (pollen limitation) or due to genetic factors. Twelve insect species were found to visit M. virginica; Bombus affinis and Bombus bimaculatus accounted for over 70% of all visits. Large patch sizes (10, 20, and 60 plants) received more insect visits than small patches (1 and 5 plants) but had a much lower proportion of their flowers visited. A patch size of five plants seems to be optimal for M. virginica since flowers within this patch size consistently set more seeds during all years of the study and received high insect visitation. Nectar robbery was found to increase seed set across all patch sizes in 1997. |
