Date: 3/30/99

Time: 10:15

Type: Symposium

Number: 107

Site and flower constancy of prairie bumblebees

*C. Reed, Department of Entomology, University of MN, St Paul, MN 55108
Contact e-mail: reedx012@maroon.tc.umn.edu

I determined bumblebee flower preferences by observing bees on flowers in native and reconstructed prairies and explored site and plant constancy of bees by conducting experiments in test plantings of prairie flowers. Over the entire flowering season, approximately 75% of second collections of individual bumblebees visiting prairie flowers were made from the same plant species visited by that individual one or more days previously. Bumblebee species varied in their constancy: Bombus griseocollis was most constant, B. impatiens was the least constant and most generalized. Plant species varied in the constancy which they received from visitors: Monarda fistulosa received the most return visits, Aster oolentangiensis the fewest return visits. Plant constancy increased with experience and was generally higher on preferred plant species than on those not preferred. Bumblebees did not preferentially seek new resources nor abandon senescing plant species. Bumblebees had short foraging lives, usually 8 days or less, and tended to be site constant; they did not usually abandon foraging sites even when resources were experimentally reduced; instead, they switched plant species on the same site. Their reluctance to switch sites increased with experience. Interactions among bee and plant species, and the site and plant constancy of bumblebees may be important in maintaining pollination on fragmented prairie sites. Bumblebee visitation to small isolated prairie remnants may be limited by the bees high site constancy and short foraging lives. Improper pollen transfer may be common among Solidago and Aster species late in the flowering season.

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