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.


Abramoff MD, Magalhaes PJ, Ram SJ (2004) Image processing with ImageJ. Biophotonics International 11(7): 36-42.

Abrol DP (2007) Honeybees and rapeseed: A pollinator-plant interaction. Advances in Botanical Research 45: 337-367. DOI:

Adler LS, Irwin RE (2006) Comparison of pollen transfer dynamics by multiple floral visitors: Experiments with pollen and fluorescent dye. Annals of Botany 97(1): 141-150. DOI:

Armstrong JM, White WJ (1935) Factors influencing seed setting in alfalfa. Journal of Agricultural Science 25: 161-79. DOI:

Bohart GE (1957) Pollination of alfalfa and red clover. Annual Review of Entomology 2: 255-380. DOI:

Boyer KJ, Fragoso FP, Dieterich Mabin ME, Brunet J (2020) Netting and pan traps fail to identify the pollinator guild of an agricultural crop. Scientific Reports 10: 13819. DOI:

Boyle NK, Kesoju SR, Greene SL, Martin RC, Walsh DB (2017) Migratory bee hive transportation contributes insignificantly to transgenic pollen movement between spatially isolated alfalfa seed fields. Journal of Economic Entomology 110(1): 6-12. DOI:

Brunet J, Stewart CM (2010) Impact of bee species and plant density on alfalfa pollination and potential for gene flow. Psyche: A Journal of Entomology 2010: Article ID 201858. DOI:

Brunet J, Thairu MW, Henss JM, Link RI, Kluever JA (2015) The effects of flower, floral display and reward sizes on bumblebee foraging behavior when pollen is the reward and plants are dichogamous. International Journal of Plant Sciences 176(9): 811-819. DOI:

Brunet J, Zhao Y, Clayton MK (2019a) Linking the foraging behavior of three bee species to pollen dispersal and gene flow. PloS ONE 14(2): e0212561. DOI:

Brunet J, Ziobro R, Osvatic J, Clayton MK (2019b) The effects of time, temperature and plant variety on pollen viability and its implications for gene flow risk. Plant Biology 21(4): 715-722. DOI:

Brunet J, Minahan DF (2023) Honey bee pollination ecology. In “Purdy J, (ed), The foraging behavior of the Honey bee (Apis mellifera L.). Elsevier, New York, New York, pp. 121-150. DOI:

Castellanos MC, Wilson P, Thomson JD (2003) Pollen transfer by hummingbirds and bumblebees, and the divergence of pollination modes in Penstemon. Evolution 57(12): 2742-2752. DOI:

Cresswell JE (1990) How and why do nectar-foraging bumblebees initiate movements between inflorescence of wild bergamot Monarda fistulosa (Lamiaceae)? Oecologia 82: 450-460. DOI:

Cresswell JE (1999) The influence of nectar and pollen availability on pollen transfer by individual flowers of oil-seed rape (Brassica napus) when pollinated by bumblebees (Bombus lapidarius). Journal of Ecology 87: 670-677. DOI:

Engel EC, Irwin RE (2003) Linking pollinator visitation rate and pollen receipt. American Journal of Botany 90(11): 1612-1618. DOI:

Foldesi R, Howlett BG, Grass I, Batáry P (2020) Larger pollinators deposit more pollen on stigmas across multiple plant species – A meta-analysis. Journal of Applied Ecology 58: 699-707. DOI:

Fragoso FP, Brunet J (2023) Differential ability of three bee species to move genes via pollen. PLoS ONE 18(4): e0271780. DOI:

Ge Y, Fu C, Bhandari H, Bouton J, Brummer EC, Wang Z-Y (2011) Pollen viability and longevity of switchgrass (Panicum virgatum L.). Crop Science 51(6): 2698-2705. DOI:

Goulson D, Hawson SA, Stout JC (1998) Foraging bumblebees avoid flowers already visited by conspecifics or by other bumblebee species. Animal Behavior 55: 199-206. DOI:

Harder LD (1990) Behavioral responses by bumble bees to variation in pollen availability. Oecologia 85: 41-47. DOI:

Harder LD, Thomson JD (1989) Evolutionary options for maximizing pollen dispersal of animal-pollinated plants. The American Naturalist 133(3): 323-344. DOI:

Harder LD, Wilson WG (1998) Theoretical consequences of heterogeneous transport conditions for pollen dispersal by animals. Ecology 79(8): 2789-2807.[2789:TCOHTC]2.0.CO;2 DOI:[2789:TCOHTC]2.0.CO;2

Irwin RE, Brody AK (1999) Nectar-robbing bumble bees reduce the fitness of Ipomopsis aggregata (Polemoniaceae). Ecology 80(5): 1703-1712.[1703:NRBBRT]2.0.CO;2 DOI:[1703:NRBBRT]2.0.CO;2

Karron JD, Mitchell RJ, Bell JM (2006) Multiple pollinator visits to Mimulus ringens (Phrymaceae) flowers increase mate number and seed set within fruits. American Journal of Botany 93(9): 1306-1312. DOI:

Kawai Y, Kudo G (2009) Effectiveness of buzz pollination in Pedicularis chamissonis: Significance of multiple visits by bumblebees. Ecological Research 24(1): 215-223. DOI:

Kearns CA, Inouye DW (1993) Techniques for Pollination Biologists. University Press of Colorado, Colorado.

Kershen DL, McHughen A (2005) Adventitious Presence: Inadvertent commingling and coexistence among farming methods. Council for Agricultural Science and Technology (CAST) Commentary QTA 2005; CAST, Ames, Iowa.

Klein AM, Steffan-Dewenter I, Tscharntke T (2003) Fruit set of highland coffee increases with the diversity of pollinating bees. Proceedings of the Royal Society B 270: 955-961. DOI:

Koch L, Lunau K, Wester P (2017) To be on the safe site – Ungroomed spots on the bee’s body and their importance for pollination. PLoS ONE 12(9): e0182522. DOI:

Lang GA, Danka RG (1991) Honey-bee-mediated cross- versus self-pollination of ‘Sharpblue’ blueberry increases fruit size and hastens ripening. Journal of the American Society for Horticultural Science 116(5): 770-773. DOI:

Larkin RA, Graumann HO (1954) Anatomical structure of the alfalfa flower and an explanation of the tripping mechanism. Botanical Gazette 116(1): 40-52. DOI:

Lehman WF, Puri YP, Garber MJ (1969) Effect of environment on quality characteristics of alfalfa (Medicago sativa L.) pollen. Crop Science 9: 560-563. DOI:

Lin L (1967) A study of factors affecting the germination of alfalfa and safflower pollen. M.S. thesis, Utah State University.

Luna VS, Figueroa MJ, Baltazar MB, Gomez LR, Townsend R, Schoper JB (2001) Maize pollen longevity and distance isolation requirements for effective pollen control. Crop Science 41(5): 1551-1557. DOI:

Marden JH (1984) Remote perception of floral nectar by bumblebees. Oecologia 64: 232-240. DOI:

McGregor SE (1976) Insect pollination of cultivated crop plants. United States Department of Agriculture – Agricultural Research Service. Agriculture Handbook No. 496.

Minaar C, Anderson B, de Jager ML, Karron JD (2019) Plant-pollinator interactions along the pathway to paternity. Annals of Botany 123(2): 225-245. DOI:

Nooten SS, Rehan SM (2020) Historical changes in bumble bee body size and range shift of declining species. Biodiversity and Conservation 29: 451-467. DOI:

Ollerton J, Winfree R, Tarrant S (2011) How many flowering plants are pollinated by animals? Oikos 120: 321–326. DOI:

Portman ZM, Orr MC, Griswold T (2019) A review and updated classification of pollen gathering behavior in bees (Hymenoptera, Apoidea). Journal of Hymenoptera Research 71: 171-208. DOI:

Prasad PVV, Boote KJ, Allen Jr. LH (2011) Longevity and temperature response of pollen as affected by elevated growth temperature and carbon dioxide in peanut and grain sorghum. Environmental and Experimental Botany 70(1): 51-57. DOI:

R Core Team (2020) R: A language and environment for statistical computing. R Foundation for Statistical Computing.

Rang ZW, Jagadish SVK, Zhou QM, Craufurd PQ, Heuer S (2011) Effect of high temperature and water stress on pollen germination and spikelet fertility in rice. Environmental and Experimental Botany 70(1): 58-65. DOI:

Rasheed S, Harder L (2003) Economic motivation for plant species preferences of pollen-collecting bumble bees. Ecological Entomology 22(2): 209-219. DOI:

Ratto F, Simmons BI, Spake R, Zamora-Gutierrez V, MacDonald MA, Merriman JC, Tremlett CJ, Poppy GM, Peh KS-H, Dicks LV (2018) Global importance of vertebrate pollinators for plant reproductive success: a meta-analysis. Frontiers in Ecology and the Environment. 16(2): 82-90. DOI:

Richards SA, Williams NM, Harder LD (2009) Variation in pollination: Causes and consequences for plant reproduction. American Naturalist 174(3): 382-398. DOI:

Santa-Martinez E, Cardoso Castro C, Flick A, Sullivan M, Riday H, Clayton MK, Brunet J (2021) Bee species visiting Medicago sativa differ in pollen deposition curves with consequences for gene flow. American Journal of Botany 108(6): 1016-1028. DOI:

SAS Institute (2016). Statistical Analysis Software (SAS) User’s Guide Version 9.4. Cary, NC: SAS Institute, Inc.

Slatkin M (1987) Gene flow and the geographic structure of plant populations. Science 236(4803): 787-792. DOI:

Snow AA, Roubik DW (1987) Pollen deposition and removal by bees visiting two tree species in Panama. Biotropica 19(1): 57-63. DOI:

Stavert JR, Bailey C, Kirkland L, Rader R (2020) Pollen tube growth from multiple pollinator visits more accurately quantifies pollinator performance and plant reproduction. Scientific Reports 10: 16958. DOI:

Thomson DM (2019) Effects of long-term variation in pollinator abundance and diversity on reproduction of a generalist plant. Journal of Ecology 107: 491-502. DOI:

Thomson JD (1986) Pollen transport and deposition by bumble bees in Erythronium: Influences of floral nectar and bee grooming. Journal of Ecology 74(2): 329-341. DOI:

Thomson JD, Goodell K (2001) Pollen removal and deposition by honeybee and bumblebee visitors to apple and almond flowers. Journal of Applied Ecology 38(5): 1032-1044. DOI:

Thomson JD, Plowright RC (1980) Pollen carryover, nectar rewards, and pollinator behavior with special reference to Diervilla lonicera. Oecologia 46: 68-74. DOI:

Thomson JD, Price MV, Waser NM, Stratton DA (1986) Comparative studies of pollen and fluorescent dye transport by bumble bees visiting Erythronium grandiflorum. Oecologia 69(4): 561-566. DOI:

Tondini F, Tavoletti S, Mariani A, Veronesi F (1993) A statistical approach to estimate the frequency of n, 2n and 4n pollen grains in diploid alfalfa. Euphytica 69: 109-114. DOI:

Tong Z-Y, Huang S-Q (2018) Safe sites of pollen placement: A conflict of interest between plants and bees? Oecologia 186: 163-171. DOI:

Wang Z-Y, Ge Y, Scott M, Spangenberg G (2004) Viability and longevity of pollen from transgenic and nontransgenic tall fescue (Festuca arundinacea) (Poaceae) plants. American Journal of Botany 91(4): 523-530. DOI:

Waser NM (1988) Comparative pollen and dye transfer by pollinators of Delphinium nelsonii. Functional Ecology 2(1): 41-48. DOI:

Wilson P, Thomson JD (1991) Heterogeneity among floral visitors leads to discordance between removal and deposition of pollen. Ecology 72: 1503-1507. DOI:

Young HJ, Dunning DW, von Hasseln KW (2007) Foraging behavior affects pollen removal and deposition in Impatiens capensis (Balsaminaceae). American Journal of Botany 94: 1267-1271. DOI:

Additional Files



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, 35, 1–13.



Early View

Similar Articles

<< < 1 2 3 4 5 6 7 8 9 10 > >> 

You may also start an advanced similarity search for this article.