The tripping mechanism of flowers affects pollen transfer dynamics


  • Molly Dieterich Mabin Vegetable Crops Research Unit, USDA Agricultural Research Service Madison, WI
  • Connor Slawin University of Wisconsin Madison
  • Amy-Mei Lynch Agricultural Research Service Research Participation Program, Oak Ridge Institute for Science and Education (ORISE), Madison, Wisconsin, USA
  • Fabiana Fragoso Agricultural Research Service Research Participation Program, Oak Ridge Institute for Science and Education (ORISE), Madison, Wisconsin, USA
  • Johanne Brunet Brunet Research



Bumble bee, Flower visits, Pollen deposition, Pollen grains on the bee's body, Medicago sativa, Tripped flowers


Insect pollinators affect pollen transfer dynamics, with consequences for pollen movement and the genetic structure of plant populations. Pollen transfer dynamics has not been previously examined in flowers with a tripping mechanism. Here we examine whether pollen accumulated on a bee’s body increases with the number of Medicago sativa L. flowers tripped by Bombus impatiens Cresson during a foraging bout, while controlling for bee body size and number of visited flowers. In a second experiment, we determine whether the number of revisits to a tripped flower increases pollen deposition onto the stigmas. We set up three M. sativa plants with a controlled number of racemes in a greenhouse room, and followed individual bees as they foraged, recording each plant, raceme, and flower visited. For pollen accumulated, we collected bees at the end of their foraging bout and counted pollen grains on their body. For pollen deposition, we collected flowers with between 0 and 6 revisits and counted the pollen grains on the stigmas. The number of pollen grains on a bee’s body increased with the number of flowers tripped in a foraging bout, but was not affected by the number of flowers visited or the size of individual bees. The number of pollen grains deposited on a stigma did not increase with the number of revisits to a tripped flower. This latter result contrasts with plants without a tripping mechanism where the number of visits increases pollen deposition and seed set. Tripping affects pollen transfer dynamics and we discuss how its effect may vary with the mode of tripping.

Author Biographies

Molly Dieterich Mabin , Vegetable Crops Research Unit, USDA Agricultural Research Service Madison, WI

Molly was a research technician in the laboratory of Dr. Johanne Brunet in Madison, Wisconson, when this work was performed.

Connor Slawin, University of Wisconsin Madison

Connor was an undergraduate at the University of Wisconsin-Madison when this research was performed, he was doing an Honors thesis in Dr. Brunet's laboratory.

Amy-Mei Lynch, Agricultural Research Service Research Participation Program, Oak Ridge Institute for Science and Education (ORISE), Madison, Wisconsin, USA

Amy was a trainee with ORISE when this research was performed, in the Brunet laboratory.

Fabiana Fragoso , Agricultural Research Service Research Participation Program, Oak Ridge Institute for Science and Education (ORISE), Madison, Wisconsin, USA

Dr. Fragoso was a postdoctoral traineed with ORISE in the Brunet laboratory when this work was performed.


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How to Cite

Dieterich Mabin , M., Slawin, C., Lynch, A.-M., Fragoso , F., & Brunet, J. (2024). The tripping mechanism of flowers affects pollen transfer dynamics. Journal of Pollination Ecology, 36, 1–13.




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