ENZ, JOHN. Department of Biological Sciences, University of Louisville, Louisville, KY 40292. - Nectar robbers and non-nectar robbers: Their visitation rates and their effects on seed set in Virginia Bluebells, Mertensia virginica (L.) Pers.
Virginia Bluebells, Mertensia virginica, (L) Pers. is a
herbaceous perennial that grows along streams and moist hillsides
within the deciduous forests of the Northeastern United States. M.
virginica produces a maximum of four nutlets per flower and is
visited by a variety of insect species, some of which exhibit nectar
robbing behavior. Nectar robbing is a behavior by which insects obtain
nectar from flowers without contacting the reproductive parts of the
flowers and has been extensively reported in the literature. In 1997,
13 patches (four contained one plant, three contained five plants,
three contained ten plants, and three contained 20 plants) were chosen
within the Horner Wildlife Sanctuary in Oldham County, Kentucky USA
where M. virginica blooms for approximately four weeks during
the month of April. The flowers in each patch were monitored and
visitation rates of nectar robbing insects and non-nectar robbing
insects were calculated. The effects on seed set of nectar robbed vs.
non-nectar robbed flowers in the different patch sizes were compared
as well. Comparisons were carried out using ANOVA statiscal procedures
in SAS. Twelve insect species were found to visit M. virginica,
although Bombus bimaculatus (non-nectar robber) and B.
affinis (nectar robber) together accounted for over 70% of all
visits regardless of patch size. B. bimaculatus spent an
average of 6.09 seconds per flower. B. affinis spent an average
of 9.7 seconds per flower on their initial visit and 4.8 seconds on
their visit to a previously robbed flower. In contrast to most studies
of other flower species in the literature, nectar robbery in M.
virginica was found to significantly increase seed set across all
Key words: bluebells, Bombus, Boragenaceae, Mertensia virginica, nectar robbery, patch size