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Effects of Multiple Visits by Carpenter Bees, Xylocopa virginica on Seed Set of Wild Lupine, Lupinus perennis (Fabaceae)Scott Hevner and Randall J. MitchellPrevious work has shown that Wild Lupine is a predominantly outcrossing species and that self pollination reduces seed set. As expected for most outcrossers, seed set is most likely limited by both pollinator service and resource availability. There is evidence that in natural populations L. perennis receives ample visits from bees (on average a flower gets 0.08 visits per hour. Additionally, dense patches of plants were found to receive more visits per 15 minute period than sparse ones. Though flowers are open and receptive for several days, receptivity peaks at days 3-6, with day 1 and 2 flowers being unreceptive. Pollen shows no changes or decreases in viability for days 1-5. Why then do only 10-20% of L. perennis flowers set fruit if the rate of pollinator visitation is sufficient? This work seeks to determine whether flowers that receive 2 or 3 visits have higher seed set and more fruits/flower than those that receive only one. Although L. perennis is pollinated mainly by bumblebees (Bombus spp), we have chosen to work with another lupine pollinator Xylocopa virginica, because its morphology makes it easier to mimic pollination behavior than that of Bombus spp.. Inflorescences on potted plants (n = 38) grown from seeds from 10 populations in the Oak Openings region were bagged to prevent natural visitation. In order to avoid possible outbreeding depression, plants were grouped for pollinations only with other plants from the same or a nearby (< 2 km) population. Hand cross-pollinations were performed using dead, wild-caught Xylocopa using a visitation design such that receptive flowers on each plant received 1, 2, or 3 "visits." Analysis of this pilot experiment showed that flowers receiving only one visit produced significantly fewer seeds per flower than those receiving 2 or 3 visits. Flowers visited once produced significantly fewer fruits per flower than those visited twice, but those visited 3 times had reduced fruit set relative to 2 visits, possibly due to breakage of stigmas receiving 3 visits. View other lab research
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